Youth sport injury research: a narrative review and the potential of interdisciplinarity

Affiliations.

  • 1 Department of Food and Nutrition, and Sport Science, University of Gothenburg, Gothenburg, Sweden.
  • 2 Faculty of Education, Monash University, Melbourne, Victoria, Australia.
  • 3 School of Health Sciences, Örebro University, Örebro, Sweden.
  • PMID: 33489308
  • PMCID: PMC7805357
  • DOI: 10.1136/bmjsem-2020-000933

To prevent sports injuries, researchers have aimed to understand injury aetiology from both the natural and social sciences and through applying different methodologies. This research has produced strong disciplinary knowledge and a number of injury prevention programmes. Yet, the injury rate continues to be high, especially in youth sport and youth football. A key reason for the continued high injury rate is the development of injury prevention programmes based on monodisciplinary knowledge that does not account for the complex nature of sport injury aetiology. The purpose of this paper is to consider and outline an interdisciplinary research process to research the complex nature of sport injury aetiology. To support our proposition, we first present a narrative review of existing youth football and youth sport injury research demonstrating an absence of paradigmatic integration across the research areas' main disciplines of biomedicine, psychology and sociology. We then demonstrate how interdisciplinary research can address the complexity of youth sport injury aetiology. Finally, we introduce the interdisciplinary process we have recently followed in a youth football injury research project. While further research is necessary, particularly regarding the integration of qualitative and quantitative sport injury data, we propose that the pragmatic interdisciplinary research process can be useful for researchers who aim to work across disciplines and paradigms and aim to employ methodological pluralism in their research.

Keywords: athlete; football; injury; methodological.

© Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.

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  • Sports injury incidence
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  • Lisa Hodgson Phillips
  • Centre for Sports Medicine, Department of Orthopaedic and Accident Surgery, Queen's Medical Centre, University Hospital, Nottingham NG7 2UH, United Kingdom
  • Correspondence to: L Hodgson Phillips

https://doi.org/10.1136/bjsm.34.2.133

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The aim of this paper is to give a “medical” viewpoint on sports injury data collection and analysis, and to emphasise the importance of epidemiological sports data collection with regard to incidence rates and exposure risk hours and highlight the need for uniform definitions within and across sport. It is designed not as a statistical or epidemiological paper but as a resource to be used by those involved in sports injury research so that they may confidently analyse, evaluate, and compare existing research and to enable them to collect accurate sports injury data in their own field.

Introduction

Sports injuries occur when athletes are exposed to their given sport and they occur under specific conditions, at a known time and place.

The last point should relate to time missed in training days as well as competitive participation and may also consider time lost to work in the case of a semiprofessional athlete. The knowledge gained from asking these questions may help us to predict and thus prevent injury.

In sports medicine, we are thus all epidemiologists “concerned with quantifying injury occurrence with respect to who is affected by injury, where and when injuries occur and what is their outcome—for the purposes of explaining why and how injuries occur and identifying strategies to control and prevent them”. 1

To interpret the literature, we must be able to discern good studies from bad, to verify whether conclusions of a particular study are valid, and to understand the limitations of a study. 2 Many studies are limited because the data collection is for injured athletes alone or risk factors alone, which does not allow the use of the epidemiological concept of athletes being at risk. There is no common operational definition of sports injury in existence at present and furthermore no set definition of severity. Some studies classify a severe injury as one that results in five games being missed, whereas others classify a severe injury as one that requires five weeks out of competition to heal; these clearly are not compatible for comparisons of sports for which more than one game is played each week. 3, 4 There is currently no set format for data collection across sports, and the size of the samples vary: some studies refer to only one team and others use multiple teams. 3, 5– 7 Therefore methodological factors alter the perception and interpretation of incidence rates.

When examining sports injury data the questions typically asked are:

is there a greater risk in one certain sport?

is there a common site and type of injury in a given sport?

who is at most risk in a team sport?

what is the participation time missed as the result of that specific injury?

The fundamental unit of measurement is rate. To calculate a valid injury rate, the number of injuries experienced (numerator data) is linked to a suitable denominator measure of the amount of athletic exposure to the risk of injury. Thus a rate consists of a denominator and a numerator over a period of time. Denominator data can be a number of different things; they could be the number of athletes in a club or team, the number of games played, the number of minutes played, or the number of player appearances. The choice of the denominator affects the numerical value of the derived data and also their interpretation. For example, injuries can be expressed as the number of injuries per game, an injury every so many minutes of play, or the number of injuries per ( x ) player appearances. 8

Incidence rates

Incidence is the most basic expression of risk. Incidence rates pertain to the number of new injuries that occur in a population at risk over a specified time period or the number of new injuries during a period divided by the total number of sportspeople at that period. Thus the epidemiological concept of athletic exposure in games or training is multiplied by the number of players participating. Incidence rates that do not consider exposure do not reliably indicate the problem and cannot be used to compare injury incidence.

Determining incidence rates

Accurate and consistent medical diagnosis is imperative. Diagnoses may be made by the doctor or physiotherapist but must be consistent throughout, with the use of set codes for site, nature, and severity of injury. All injuries should be recorded, including transient injuries—that is, those that require medical attention but result in no time lost to training or playing. Time lost from participation must be recorded accurately, using both training and game/competitive participation data, in days lost as well as games and weeks lost. Many studies exclude training injuries and training time lost, using only those injuries that occur in a game or that require a competitive game to be missed. 3, 9 These studies lose valuable data and fail to portray the true injury picture of the sport. If training information is excluded, then the data only represent the tip of the iceberg—submerged missed data may include the effects of training injuries or, more importantly, the training time lost on the player, his/her fitness, and ultimately his/her career. The same argument can be used to show the importance of including transient injuries in the data analysis. Excluding these injuries gives a false picture of the injuries sustained in a given sport.

Coding of injury diagnosis

Coding and recording of injuries should be through the consistent use of a set of established definitions of injury, which are expansive and descriptive to avoid subjectivity. Standard classifications of diagnoses are in existence such as the International Classification of Diseases; however, these are often not specific enough and thus not of any use for sports injury data collection. In contrast, there is the Orchard Codes system, which is very descriptive and expansive and may be used in this type of research. A single person should record the information where possible to achieve greatest intra-rater reliability. Time lost from sport participation must be considered an objective measure that is not sensitive to the concept of returning to play when the athlete is not fully healed and must always be referred to as a filter when conclusions on sports injury data are drawn. Athletes are often paid professionals and as such do not wish to miss a training or competitive/playing session, which could result in loss of their team place in the next game or their wage at the end of the week. Athletes are eager to participate and thus always challenge the healing process as they almost always aim to return to competition much sooner than the lay person. 10 We do not have any reliable criteria on return to sport.

Study design

The US Preventative Services Task Force in 1989 established a hierarchy of evidence in which greater weight was given to study designs in decreasing order of importance. 11 Random control trials were rated first; these expose some subjects, but not others, to an intervention—for example, risk of injury. Therefore this type of research is more clinical in nature and not typically appropriate for the study of injury patterns. Cohort studies were rated next; this type of study monitors both injured and non-injured athletes, thereby providing results on the effects of participation, and are ideally prospective in nature. Case-control was the third type of study, monitoring only those athletes who suffered an injury and are typically more retrospective in nature. These make up the vast majority of sports injury studies at present; however, we should recognise that multiple anecdotes do not add up to an evidence base.

Weaknesses in sports injury epidemiology research

Retrospective data are used which may lead to bias.

Multiple injury recorders leading to a lower inter-rater reliability.

Single or part season's data analysed.

Single team analysed.

Injury cases documented are not adjusted for exposure risk hours of training or playing.

Comparisons made with other studies that have not used the same injury coding or methodology (may not even be of the same sport).

Studies should have validity and reliability. The former is defined as the extent to which you measure what you intended to measure and is usually compared against a yardstick. Sports injury incidence at present has no yardstick against which comparisons can be made. Reliability is the ability to produce the same results on more than one occasion and is dependent on inter-rater or intra-rater data collection. For accurate injury incidence, reliability is imperative. 12

Sample size influences results. It is impossible to compare studies in which various sample sizes—that is, one team or many—have been used, unless adjustments for exposure have been made and this is clearly stated in the methods. Studies on one particular sports team, however, can be powerful if the number of injuries incurred is large enough to show statistical significance. 13

The type of statistical analysis is directly related to the methodology of the study. For example, the χ 2 test can be used to assess the differences between observed and expected injuries in a season or number of seasons. Multiple regression and multiple variate analyses may be chosen to assess the influence of independent factors on the injuries incurred—for example, the player position or the hardness of the ground. The calculation of incidence rates has been identified as a critical feature of sound epidemiological sports injury studies. 14

As a footnote, it should be mentioned that any patient injury information collected must always be confidential.

Exposure risk hours and rates per 1000 hours

The way in which incidence is expressed has also been shown to affect the calculation/interpretation of incidence rates. Increasingly, incidence rates in all sports are being expressed as rates per 1000 hours. This is a good approach and allows some comparison across sports. However, a further refinement of the calculation of incidence rates is to measure the actual exposure time at risk. Thus expected injuries are calculated using player exposure/risk hours. These risk hours should ideally include training time as well as competitive participation. 13, 15

The following is an example of how exposure/risk hours are calculated in a team sport, specifically rugby league. There are 13 players of one team on the field at any one time. The duration of the game is 80 minutes (1.33 hours). Thus there are 17.33 player exposure/risk hours per team per game of rugby league (13 × 1.33). Over an average season—for example, 30 games—there may be 520 player exposure/risk hours (13 × 1.33 × 30).

To calculate the incidence in relation to these exposure hours, the total number of injuries recorded over a period is divided by the total exposure for that period, and the result multiplied by 1000 to obtain the rate per 1000 hours. This period could be one game, several games, or a whole season or number of seasons. To see if there are significant differences across games or seasons, observed and expected injuries can be used. Observed injuries are those recorded over the period under consideration. Expected injuries are calculated by dividing the total injuries—for example, over four seasons—by the total exposure—for example, for the same four seasons—and multiplying the result by the exposure for the period under consideration—for example, one season only—giving an expected injury case for that one season. Significance tests may then be applied.

The relevance of recording and analysing data in this way is shown below taking data from a previous study. 13 Figure 1 shows the number of injury cases recorded over four rugby league seasons at one British professional rugby league club (1993–1996 inclusive). On initial observation, there does not appear to be a significant difference across the four seasons, and the observer may even say that the injuries were in fact lower over the last two seasons. However, in fig 2, which is for the same four seasons but the data are adjusted for exposure/risk hours and presented as rates per 1000 hours, the true picture is disclosed. An obvious increase in injury incidence is seen. In truth, in the 1996 season, the incidence of injury was almost double that of the first season recorded (1993/1994). Excluding exposure time at risk prevents the true picture from being seen. This can be highlighted by the fact that, during the 1993/1994 season, there were 35 games played (605.15 exposure hours) and in 1996 only 21 games were played (363.09 exposure hours); however, observe the difference in injury incidence again. Not adjusting for exposure/risk hours but only commenting on total injury cases is a fatal flaw in sports injury data presentation.

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Game injury statistics showing number of injury cases per season.

Game injury statistics showing rates per 1000 hours per season.

Strengths in sports injury epidemiology research

Using one recorder to diagnose and document injuries gives a high intra-rater reliability.

Incidence rates are used and adjusted for exposure.

Training injuries are included.

Time lost to competitive participation plus time lost to training and work also documented.

Prospective studies conducted using descriptive set injury coding definitions and methodology.

Filters recognised and referred to.

Comparisons made with similar studies but acknowledging the differences in diagnostic coding and definitions of severity.

Acknowledging where professional sport is compared with amateur sport.

Using more than one team where possible: improved generalisability.

If we apply the above to what we already know clinically, we may help to predict and prevent future injury occurrence. Thus accurate data collection could be essential in the prevention of injuries. If specific influences are identified as a contributing factor to the risk of injury and supported by scientific data collection, then the rules of the sport may be changed to prevent this happening again. This will have the effect of making our athletes as injury free as possible and may even help to lengthen their time in competitive participation.

Ideal study

Cohort design (injured and non-injured athletes observed).

Conducted over several teams.

Longitudinal prospective data collection.

One recorder where possible (high intra-rater reliability).

Uniformity of injury definition across sports.

Specific definitions of injury severity so comparisons between studies can be made accurately.

Exposure hours used to express incidence rates for competitive participation and training.

Acknowledgement of existing filters.

Acknowledgments

I would like to thank Dr Mark E Batt for his help and advice on preparing this paper.

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  • ↵ US Preventative Services Task Force. Guide to clinical preventative services: an assessment of the effectiveness of 169 interventions. Report of the US Preventative Services Task Force. Sydney: Williams & Wilkins, 1989.
  • ↵ Lower T. Injury data collection in the rugby codes. Aust J Sci Med Sport 1995 ; 27 : 43 –7. OpenUrl PubMed
  • ↵ Hodgson Phillips L, Standen P, Batt ME. Effects of seasonal change in rugby league on the incidence of injury. Br J Sports Med 1998 ; 32 : 144 –8. OpenUrl Abstract / FREE Full Text
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  • Published: 05 December 2018

Overuse injuries in sport: a comprehensive overview

  • R. Aicale 1 ,
  • D. Tarantino 1 &
  • N. Maffulli 1 , 2  

Journal of Orthopaedic Surgery and Research volume  13 , Article number:  309 ( 2018 ) Cite this article

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The absence of a single, identifiable traumatic cause has been traditionally used as a definition for a causative factor of overuse injury. Excessive loading, insufficient recovery, and underpreparedness can increase injury risk by exposing athletes to relatively large changes in load. The musculoskeletal system, if subjected to excessive stress, can suffer from various types of overuse injuries which may affect the bone, muscles, tendons, and ligaments.

We performed a search (up to March 2018) in the PubMed and Scopus electronic databases to identify the available scientific articles about the pathophysiology and the incidence of overuse sport injuries. For the purposes of our review, we used several combinations of the following keywords: overuse, injury, tendon, tendinopathy, stress fracture, stress reaction, and juvenile osteochondritis dissecans.

Overuse tendinopathy induces in the tendon pain and swelling with associated decreased tolerance to exercise and various types of tendon degeneration. Poor training technique and a variety of risk factors may predispose athletes to stress reactions that may be interpreted as possible precursors of stress fractures. A frequent cause of pain in adolescents is juvenile osteochondritis dissecans (JOCD), which is characterized by delamination and localized necrosis of the subchondral bone, with or without the involvement of articular cartilage. The purpose of this compressive review is to give an overview of overuse injuries in sport by describing the theoretical foundations of these conditions that may predispose to the development of tendinopathy, stress fractures, stress reactions, and juvenile osteochondritis dissecans and the implication that these pathologies may have in their management.

Conclusions

Further research is required to improve our knowledge on tendon and bone healing, enabling specific treatment strategies to be developed for the management of overuse injuries.

The specific definition of overuse injury was most commonly based on the concept of an injury occurring in the absence of a single, identifiable traumatic cause [ 1 ]. Professional soccer players sustain on average 2.0 injuries per season, which cause them to miss 37 days in a 300-day season on average [ 2 ]. Following the updated injury etiology model, training and match load contribute, together with intrinsic and extrinsic risk factors, to the multifactorial and dynamic etiology of injury [ 3 ]. Not only excessive loading and insufficient recovery, but also underpreparedness may increase injury risk by exposing players to relatively large changes, or spikes, in load during periods with higher training and match loads [ 4 ].

The tendons transfer the force produced from muscular contraction to the bone. In most instances, sports-related tendinopathies present well-defined histopathological lesions, providing an explanation for the chronicity of symptoms which often occur in athletes with tendinopathies [ 5 , 6 , 7 , 8 ].

The aim of the present article is to investigate the physiopathology, clinical presentation, diagnostic tools, and management of the most common overuse sport injuries. In particular, we focus on tendinopathy, stress reaction, stress fracture, and juvenile osteochondritis dissecans, which are the most frequent lesion caused by overuse. Furthermore, in the first part of this study, to better understand the changes of the bone, muscle, and tendon structures, we mention different mechanisms present in an overuse situation.

Overuse tendinopathy induces in the affected tendon pain and swelling, and associated decreased load tolerance and function during exercise of the limb [ 9 , 10 ]. Various types of tendon degeneration have been described at electron microscopy, namely (a) hypoxic degeneration, (b) hyaline degeneration, (c) mucoid or myxoid degeneration, (d) fibrinoid degeneration, (e) lipoid degeneration, (f) calcification, and (g) fibrocartilaginous and bony metaplasia [ 11 ]. Healing of tendinopathic tendons relies on the intrinsic ability of tenocytes to respond to the stimulus induced by the injury to the surrounding tissue matrix [ 12 , 13 ] and consists of a cellular response including apoptosis (programmed cell death), chemotaxis, proliferation, and differentiation [ 14 ]. The mechanism underlying the precise sequence of these events, which balance the effectiveness of healing and any subsequent predisposition to repetitive damage, remains obscure.

The essence of tendinopathy is a “failed healing response.” This model suggests that, after an acute insult to the tendon, an early inflammatory response that would normally result in successful injury resolution veers toward an ineffective healing response [ 15 ], with degeneration and proliferation of tenocytes, disruption of collagen fibers, and subsequent increase in non-collagenous matrix [ 7 , 16 , 17 , 18 , 19 ] (Table  1 ).

Poor training technique and a variety of risk factors may predispose players to lower limb overuse injuries affecting the bone, including stress reactions to full-fledged stress fractures. The underlying principle of the bone response to stress is Wolff’s law, whereby changes in the stresses imposed on the bone lead to changes in its internal architecture [ 20 , 21 ]. Stress fractures, defined as microfractures of the cortical bone tissue, affect thousands of athletes per year [ 22 , 23 ]. Certain subpopulations, including runners, gymnasts, and female athletes, exhibit higher rates of stress fractures [ 24 , 25 ]. If left untreated, a stress fracture can progress to a complete fracture of a bone, which may require surgical fixation [ 26 ]. In addition, factors contributing to stress fractures increase the risk for osteoporosis, a substantial long-term health concern [ 27 ].

Stress reactions of the musculoskeletal system may be interpreted as possible precursors of stress fractures. Biological tissues, in contrast to artificial products, can react in numerous and complex ways. This can lead not only to a continual weakening of the tissue, but also to adaption phenomena in response to overuse. The causes of such stress reactions are still unclear.

Juvenile osteochondritis dissecans (JOCD) is a frequent cause of pain in adolescents, both athletes and non-athletes. JOCD is characterized by delamination and localized necrosis of the subchondral bone, with or without the involvement of the overlying articular cartilage [ 28 , 29 , 30 , 31 ]. The etiology remains unclear, but repetitive microtrauma, such as that typical of overuse injury, is considered the significant factor leading to JOCD [ 28 , 29 ].

The role of inflammation and molecular factors in overuse injuries

The effects of an altered inflammatory response.

In this model, the question arises as to why the healing response is successful in some individuals but fails in others. More importantly, can we identify factors which may increase the risk of this ineffective healing response? For example, the incidence of tendinopathy is increased in individuals with obesity and decreased insulin sensitivity, as seen in patients with type 1 and type 2 diabetes mellitus (T1/T2DM) [ 10 , 32 , 33 , 34 ]. Evidence for a chronic, low-grade inflammatory state in obesity is represented principally by marked increases in plasma levels of proinflammatory cytokines such as tumor necrosis factor (TNF)-a and interleukin (IL)-6, and proinflammatory chemokines such as monocyte chemoattractant protein (MCP)-1 [ 34 ].

Patients with type 1 and type 2 diabetes exhibit a less effective healing response [ 35 ]. Recently, it has been demonstrated the presence of an independent relationship between impaired insulin sensitivity and the development of chronic low-grade inflammation through a protein, the levels of which are normally physiologically inhibited by insulin, called FOXO1, a key upregulator of the proinflammatory cytokine IL-b [ 35 ].

Considering the influence that a prolonged state of low-grade systemic inflammation may have on the healing process after acute tendon injury, it must be appreciated that tendon healing is a delicate and prolonged process even under optimal physiological conditions [ 10 , 34 ]. Even minor disruptions to any of the noted healing stages could result in a much more prolonged and complicated resolution of injury. Similarly, if several minor disruptions to this process occur (in the form, for example, of microtraumas), complete healing and resolution of injury become progressively unlikely [ 10 ].

The acute inflammatory phase noted in the first few days after a tendon injury is marked by the migration of inflammatory cells such as macrophages and monocytes [ 36 ]. As the chronic inflammatory state in obesity is associated with a reduction in the numbers of circulating macrophages [ 33 ], such a decrease in the availability of circulating cells may result in the mounting of a less effective early healing response.

Such findings are consistent with a post-injury state of “failed healing,” in which evidence of matrix disorganization, increased amounts of extracellular ground substance, and a degree of separation between collagen fibers has been noted [ 37 , 38 ], with associated greater vulnerability to future mechanical strain [ 10 ].

This relationship may help to explain the influence that mechanical overuse plays in the development of tendinopathy. Examining the incidence of tendinopathy among patients with type 2 diabetes, unilateral or bilateral tendinopathy was found in 32% of the diabetic patients studied versus 10% of controls [ 39 ]. Also, when the incidence of unilateral tendinopathy among diabetic patients was examined more closely, 45% were found to occur in the right shoulder compared with just 27% in the left shoulder [ 33 ].

Molecular factors in overuse injury

A lack of exposure to adequate levels of physiological stress over a prolonged time period or “underloading” may paradoxically predispose to overload injury [ 34 ]. An underloaded tendon may become unable to cope with increased demands imposed on it. Thus, underuse of a tendon may result in an imbalance between matrix metalloproteinases and their inhibitors (tissue inhibitors of matrix metalloproteinases), with resultant tendon degradation [ 34 ].

Molecular agents may link the events of tendon degeneration and ineffective tendon healing with the production and persistence of reactive oxygen species within both the intra- and extra-cellular milieu of the tendon tissue [ 40 ]. The reactive oxygen production is strongly influenced by lifestyle factors, e.g., nutrition and the intensity and frequency of exercise.

The term reactive oxygen species (ROS) encompasses reactive species derived from oxygen. A free radical is any species capable of independent existence that contains one or more unpaired electrons [ 41 ]. Physiologically relevant ROS include the superoxide anion (O 2− ), hydrogen peroxide (H 2 O 2 ), hydroxyl radical (HO − ), singlet oxygen ( 1 O 2 ), and peroxyl radicals (RO 2− ). An inter-related group of radical and non-radical reactive species is the reactive nitrogen species (RNS) [ 42 , 43 , 44 ].

The principal site for ROS formation in non-stressed cells is the mitochondrial respiratory chain. This series of coupled redox reactions leads to the formation of ATP with molecular oxygen the ultimate electron acceptor and being reduced to water [ 45 , 46 ].

ROS may mediate processes of cell proliferation [ 47 ], differentiation [ 48 ], and adaptive responses [ 45 , 49 ]. At higher levels, ROS may initiate and/or execute the demise of the cell through programmed as well as necrotic cell death mechanisms [ 50 , 51 , 52 ].

Traditionally, ROS are viewed as imposing cellular and tissue damage via lipid peroxidation, DNA damage, and protein modification [ 45 , 53 ]. However, in themselves, O 2− and H 2 O 2 are not potent biological oxidizers [ 45 ], although certain proteins may be prone to direct modification by these species. ROS production is involved in various cancers (e.g., the lung, colon), coronary heart disease, autoimmune diseases, etc. [ 41 ]. Furthermore, ROS are implicated in overuse exercise-related damage in muscle [ 49 ] and may impair fracture healing in the bone [ 54 ].

Cells and tissues contain many antioxidant molecules, but many antioxidants are also capable of acting as pro-oxidants [ 55 ]. For example, ascorbic acid in the presence of iron/copper generates HO − , and with flavonoids may generate O 2− [ 55 ].

ROS may be involved in tendinopathies or other stress reactions: indeed, synthesis, structure, and integrity of connective tissues are influenced by them. Reactive species may be produced within the intra- and extra-tendinous environment. Evidence suggest that ROS constitute a stress factor during not-hard exercise [ 49 ]. Excessive exercise induces elevated ROS production, primarily from mitochondria [ 56 ]. Exercise also stimulates the immune response [ 56 , 57 , 58 ], with increased leucocyte numbers, in particular granulocytes. Exhaustive exercise in cross-country skiers produced neutrophil mobilization and increased ROS generation on subsequent stimulation. Enhanced phagocytic O 2− generation accurs approximately 24 h after exhaustive exercise [ 59 ].

Increased phagocyte activity probably does not contribute to elevated ROS production during short-term exercise, but may act as a secondary source of ROS during recovery from heavy exercise [ 59 ].

During cyclical tendon loading, the period of maximum tensile load is associated with ischemia, and relaxation with reperfusion. This restoration of normal tissue oxygenation may lead to enhanced ROS production [ 59 , 60 ]. There is potential for re-oxygenation resulting in a cycle of enhanced ROS production, most probably at sublethal levels within the non-degenerate tendon [ 40 ].

Hyperthermia is a feature of tendon use inducing ROS production. During exercise, the central core temperature of the muscles can exceed 47 °C [ 49 ], a temperature resulting in increased ROS production in mitochondria [ 49 ]. Similarly, in exercising the tendon, core temperatures may reach 45 °C, contributing to their damage [ 60 ].

During fibrogenesis, ROS, primarily derived from specialized phagocytes and products arising from lipid peroxidation, induce overexpression of fibrogenic cytokines and increase the synthesis of collagen [ 61 ]. Endogenous and exogenous ROS may also exert effects on tenocyte proliferation, development, and viability, with implications on both tendinopathy and post-rupture healing [ 62 ]. Tenocytes are motile and highly proliferative and rapidly increase in number following injury [ 62 ].

Tenocyte numbers are altered in degenerated tendons, and the selective deletion of tenocytes from damaged tendon may be a factor in degeneration, but also a prerequisite to healing. Heightened levels of ROS production may not only induce cell death, but also determine the mechanistic form of that death, in particular, the ratio of programed cell death (PCD): necrosis [ 51 ].

High concentrations of H 2 O 2 can prevent apoptosis. Conversely, “bursts” of ROS [ 51 , 63 ] and reductions in antioxidant enzyme activity [ 64 ] frequently accompany the induction of apoptosis, and oxidative stress is a common feature of the late phase of apoptosis [ 51 ]. For example, the pro-apoptotic transcription factor p53 demonstrates impaired DNA binding following exposure to ROS. However, it can induce apoptosis by induction of enhanced mitochondrial ROS generation [ 65 ].

Overuse sport injuries

Tendinopathy: consideration and management.

Tendinopathy has been hypothesized to result from inflammatory changes in the tendon, and secondary to its frequent or excessive use, assigning the label of “tendinitis” or “tendonitis” to such a presentation [ 9 , 10 , 66 ]. However, anti-inflammatory agents are largely unsuccessful in the treatment of the condition [ 15 , 66 ], and with the increase in histopathological data showing degenerative changes but little inflammation, the inflammatory hypothesis in overuse tendon injury became decreasingly popular [ 10 , 15 , 36 , 67 ]. The term “tendonitis” became increasingly replaced by “tendinosis” [ 36 ], but a definitive diagnosis of either should only be made following histopathological confirmation [ 15 , 36 , 67 ].

However, it became evident that tendon biopsies from operated patients were likely to represent the end stage of a pathological continuum [ 10 ], probably demonstrating a different histopathological picture to that which would be seen in the initial stages of injury [ 36 , 67 ]. This was supported by evidence from human and animal biopsies that showed that both peritendinitis and a failed healing response, wrongly labeled “tendinosis,” could be present concurrently [ 36 ].

In tendinopathic lesions, the parallel orientation of collagen fibers is lost, with a decrease in collagen fiber diameter and in the overall density of collagen. Collagen microtears may also occur and may be surrounded by erythrocytes, fibrin, and fibronectin deposits. Normally, collagen fibers in tendons are tightly bundled in a parallel fashion. In tendinopathic samples, there is unequal and irregular crimping, loosening, and increased waviness of collagen fibers, with an increase in type III (reparative) collagen [ 17 , 19 , 68 , 69 , 70 , 71 ]. Vascularity is typically increased, and blood vessels are randomly oriented, sometimes perpendicular to collagen fibers [ 72 , 73 ]. Inflammatory lesions [ 72 , 73 , 74 , 75 ] and granulation tissue [ 74 , 75 ] are infrequent and, when found, are associated with partial rupture: therefore, tenocytes are abnormally plentiful in some areas [ 76 , 77 ].

Tendinopathies are common in elite and recreational athletes and are traditionally considered overuse injuries, involving excessive tensile loading and subsequent breakdown of the loaded tendon [ 78 , 79 ]. Although acute traumatic conditions such as ligament and muscle tears receive much attention in the lay press, tendinopathies account for much of the lost time in practice and competition [ 80 , 81 ].

Biopsy studies have shown that classic inflammatory changes are not frequently seen in chronic tendon conditions and that histopathology features in tendinopathic tendons are clearly different from normal tendons [ 82 , 83 ].

All tendons can develop tendinopathy [ 5 , 84 ]. The supraspinatus, common wrist extensor, quadriceps, patellar, posterior tibialis, and Achilles tendons are probably the most commonly affected tendons. Insertional tendinopathy is one of the most common forms of tendinopathy, and, in particular, the supraspinatus, common wrist extensor, quadriceps, and patellar tendons are most affected by it [ 84 ]. The Achilles tendon, on the other hand, can present tendinopathy of the main body of the tendon, paratendinopathy and insertional tendinopathy, each with different clinical features and management implications [ 84 ].

Achilles tendinopathy (AT) is a common overuse injury among athletes, with an increasing incidence over the past 30 years [ 85 , 86 ]. AT is particularly prevalent in athletes whose sport involve running and jumping activities [ 87 , 88 ] and is thus common in sports such as soccer. In the four principal soccer leagues in England, there are an average of 3.5 Achilles tendon-related injuries per week in the preseason and an average of one injury per week in the competitive season [ 89 , 90 ].

Tendinopathies may result from excessive loading of the tendon and subsequent mechanical breakdown of the loaded tendon [ 91 ]. Theoretically, repeated microinjuries may occur, and the tendon may be able to heal a certain level of microinjury. However, as training and heavy loading of the tendon continues, this healing process may be overwhelmed, and a further injury ensues.

Other factors in addition to training errors may lead to increased loading of the tendon, such as poor technique [ 92 , 93 ] or inadequate athletic equipment [ 94 ]. Also, intrinsic factors, such as the status of the muscles, ligaments, and bones surrounding the tendon, may alter the level of the load on the tendon [ 19 ]. Recent biomechanical studies about failure modes of the muscle-tendon units have shown that failure occurs within the muscle near the muscle-tendon junction [ 95 , 96 ].

Relatively, little is known about the role of neuronal regulation in tendinopathy, and the source of pain has not been clarified yet [ 97 ]. The presence of pain in tendinopathy requires not only mechanical changes, but also alterations in the way the local cells and the peripheral nerves react to this change. A recent systematic review showed that the peripheral neuronal phenotype is altered in tendinopathy [ 97 ] and that the peripheral and central pain processing pathways are important factors in the pathogenesis of painful human tendinopathy. Changes in the peripheral neuronal phenotype may be the primary source of pain [ 97 ] .

Clinical history and examination are essential for diagnosis. Clinically, tendinopathy is characterized by pain, swelling (diffuse or localized), and impaired performance [ 6 ].

Pain is the cardinal symptom, and it occurs at the beginning and a short while after the end of a training session. As the pathological process progresses, pain may occur during the entire exercise session, and, in severe cases, it may interfere with the activities of daily living. Clinical examination is the best diagnostic tool. In tendinopathy of the main body of the Achilles tendon, the location of pain is 2–6 cm above the insertion into the calcaneum, and pain on palpation is a reliable and accurate test for diagnosis [ 98 ].

In addition to the swelling on the posteromedial aspect of the tendon and palpation pain, some clinical tests have been described for non-insertional AT diagnosis. They can be divided into palpation tests (tendon thickening, crepitus, pain on palpation, the Royal London Hospital (RLH) test, the painful arc sign) and tendon loading tests (pain on passive dorsiflexion, pain on single heel raise, and pain on hopping).

Plain radiography can be used to diagnose associated or incidental bony abnormalities [ 99 ].

Ultrasound is an effective imaging method since it correlates well with the histopathologic findings despite being an operator-dependent [ 100 ]. MRI studies should be performed only if the ultrasound scan remains unclear. The ultrasound (US) signs of hypoechoic areas, spindle-shaped thickening, neovascularization, and paratenon blurring [ 101 ] are associated with AT [ 102 ] and may be potential predictors of future tendinopathy [ 87 ] when present in asymptomatic individuals.

The first line of management for AT is conservative, and different treatments such as nonsteroidal anti-inflammatory drugs, physical therapy, taping, cryotherapy, shock wave therapy, hyperthermia, and various peritendinous injections have been used with varying success [ 103 ]. The management of AT lacks strong evidence-based support, because few treatment modalities have been investigated in randomized controlled trials [ 103 ], and approximately 25% of patients do not respond to conservative management [ 104 ]. Good results have been reported with eccentric exercises [ 105 , 106 ], but these alone may not work in all patients [ 107 ], and their mechanism of action is not completely understood [ 106 ]. These are the most effective conservative treatment for non-insertional AT. The most commonly used protocol is the Alfredson’s protocol: the exercises are performed in three sets of 15 repetitions, twice a day for 12 weeks [ 108 ].

ESWT, when compared with eccentric strengthening in a RCT, showed comparable outcomes, with 60% of the patients at least significantly improved in both of the treatment groups, and significantly better than those in the “wait and see” control group [ 109 ]. Where available, ESWT should probably be a second-line treatment.

Various injection therapies have been proposed [ 110 ]. In a recent systematic review [ 111 ], only ultrasound-guided sclerosing polidocanol injections seemed to yield promising results, but these results do not appear to have been duplicated outside Scandinavia [ 112 ]: indeed, Ebbesen et al. [ 113 ], in a RTC, concludes that polidocanol injections are a safe treatment, but in the mid-term, the effects are the same of a placebo treatment for chronic Achilles tendinopathy. The use of platelet-rich plasma (PRP) is growing exponentially, especially among sports medicine physicians, but the only well-designed RCT published on PRP in AT showed no significant difference in pain or activity level between PRP and saline injection at 6, 12, or 24 weeks when combined with an eccentric stretching program [ 114 ]. High-volume image-guided injections (HVIGI) significantly reduce pain and improve function in patients with resistant AT [ 115 ]. A recent study found relevant clinical results with the contemporaneous administration of platelet-rich plasma and high-volume image-guided injections of saline treatments, which influence tendon repair by different mechanisms and grants a greater improvement for patellar tendinopathy [ 116 ].

Conservative treatment fails in between one quarter and one third of patients, and surgical intervention is required [ 117 ]. Minimally invasive therapies which strip the paratenon from the tendon, either directly [ 118 ] or indirectly with high-volume fluid injection [ 115 ], have shown good initial results in relieving the symptoms of non-insertional AT [ 103 , 119 ].

Another technique consists in multiple percutaneous longitudinal tenotomies, which can be performed under ultrasound guidance [ 120 , 121 ]. Minimally invasive surgical treatment would appear to be a useful intermediate step between failed conservative treatment and formal open surgery [ 103 ].

The high recurrence rate (27%) for AT when managed conservatively reflects the chronic and recurrent character of this condition. The frequent relapse of symptoms when players return to football after a short rehabilitation period could be explained if the pain is only the tip of the iceberg. Therefore, it could be suggested that a longer rehabilitation period at the first signs of AT could be beneficial to avoid recurrences [ 122 ].

Stress reaction and stress fracture

Stress reactions may be interpreted as precursors of stress fractures [ 123 ]. The causes of such stress are still unclear. For example, it is unknown to what extent a predisposition to these stress symptoms by mechanical stress alone or whether other factors such as physical condition, nutrition, or even hormone balance come in to play. Early diagnosis considerably reduces the impairment of the healing process. The treatment of a stress reaction should be the same as for a diagnosed stress fracture [ 123 ]. Much of our epidemiological knowledge about stress fractures originates from research on military recruits [ 124 ] and high school athletes [ 25 ].

The response of the bone to repetitive stress is increased osteoclastic activity over osteoblastic new bone formation, which results in temporary weakening of the bone [ 125 ]. The eventual adaptive response is periosteal new bone formation to provide reinforcement [ 126 ]. However, if physical stress continues, an osteoclastic activity may predominate, resulting initially in microfractures (commonly seen as bone marrow edema on MRI, consistent with a stress reaction), and eventually, a true cortical break (stress fracture) may result [ 1 ]. If strain becomes excessive or adequate rest is not implemented, stress reaction and eventually a stress fracture can results [ 126 , 127 ].

There is a difference between stress fractures from fatigue and insufficiency type. Fatigue fractures are the typical overuse stress fractures observed in athletes and military recruits with normal bone density. They result from an imbalance in the ability of the bone to keep up with skeletal repair from an excessive bone strain with progressive accumulation of microdamage [ 126 ]. An insufficiency fracture is seen in those with low bone mineral density (BMD), such as runners with the female athlete triad; metabolic bone disease; or osteoporosis. Insufficiency fractures result from poor bone remodeling (increased resorption and depressed formation) in response to normal strain [ 126 ].

Rizzone et al. [ 128 ] investigated the epidemiology of stress fractures in 671 collegiate student-athletes for the academic years 2004–2005 through 2013–2014. The rate of stress fracture was highest among endurance athletes and higher in women than in men. Higher rates among female athletes were found not only in cross-country athletes, indoor track, and outdoor track athletes, but also in basketball and soccer athletes. Twenty-two percent of stress fractures were recurrent, and 20% resulted in season-ending injuries [ 128 ].

The number of reports in the literature of lower extremity stress fractures in female soccer athletes is small [ 129 ]. Of the 18 million Americans who play soccer, 78% are younger than 18 years and more than 40% are female [ 130 ]. Women collegiate soccer increased from 1855 athletes on 80 teams during the 1981–1982 seasons to 22,682 athletes on 956 teams during the 2007–2008 seasons, making women’s soccer the NCAA sport with the greatest number of athletes [ 131 ]. A study of 2016 [ 132 ] showed that elite female soccer athletes are susceptible to stress fractures and menstrual dysfunction and experience delayed onset of menarche despite normal BMI and appropriate body perception and attitudes toward eating. Education about the detrimental effects of menstrual dysfunction and the importance of adequate energy balance and nutritional requirements should be encouraged to minimize the risk for poor bone health, manifesting as a stress fracture in the short term and osteoporosis over the long term in these athletes [ 132 , 133 ].

The typical history of a stress fracture is localized pain of insidious onset which is initially not present at the start but occurs toward the end of a run. A sign of a more advanced fracture is pain progressing to occur during non-running-related activities, affecting day-to-day walking [ 126 ].

Defining the causative risk factors for stress fractures is difficult because there are many interrelated variables which make risk assessment problematic to study independently. Extrinsic and intrinsic factors may lead to stress fractures [ 126 , 133 , 134 ]. An increase in frequency, duration, or intensity of training load is often cited as a primary risk factor [ 135 ]. Hard training surfaces are also factors associated with lower-limb overuse injuries [ 135 ]. Training in shoes older than 6 months is a risk factor for stress fractures, likely related to the decrement in shock absorption as shoes age [ 135 ].

Regarding the intrinsic factors, Bennell et al. [ 22 ] demonstrated that smaller calf girth and less muscle mass in the lower limb of female runners was associated with a higher incidence of stress fractures. Kinematic and kinetic biomechanical variables have also been recently studied as potential risk factors for stress fractures; for example, in runners, an excessive hip adduction and rear-foot eversion are predictors of tibial stress fractures [ 136 ].

The hallmark physical examination finding is focal bony tenderness. Overlying swelling, erythema, or warmth are other potential examination findings. Less sensitive tests for fractures of long bones include the fulcrum test and hop test [ 137 ]. A functional kinetic chain assessment is useful to elucidate biomechanical factors that may predispose the runner to injury. Evaluating muscle imbalances, leg-length discrepancies, foot mechanics, genu varum, and femoral anteversion is appropriate because all have been associated with stress fractures [ 137 ].

Radiographic imaging should be used to supplement the clinical history and physical examination if uncertainty persists. Imaging can also be used to grade the severity of an injury and can thus be helpful in guiding treatment. CT is best used to differentiate lesions seen on a bone scan that may mimic stress fracture, including osteoid osteoma, osteomyelitis, and malignancy [ 138 ]. MRI is becoming the imaging study of choice, with many considering MRI the gold standard for the evaluation of bony stress injuries [ 139 ].

It is not only important to understand the significance of protection and rest, but also to understand the predisposing factors to the injury. Treatment is the time to explore and treat the contributing risk factors. For example, if low bone density is found, appropriate treatment is mandatory; if biomechanical issues are identified, and inappropriate shoes and training are determined, and specific rehabilitation is required [ 126 ].

Therapeutic ultrasound and electrical stimulation are purported modalities for enhancing the healing rate of fractures. Therapeutic ultrasound has been demonstrated to decrease healing time in acute tibial shaft, in distal radius fractures, and in navicular stress injuries [ 140 , 141 ]. Electrical stimulation for bone growth has some support in delayed unions and non-unions, but only in uncontrolled trials for stress fractures [ 142 ].

Juvenile osteochondritis dissecans (JOCD)

JOCD is a frequent cause of knee pain in adolescent athletes and non-athletes, with an incidence higher in boys than in girls [ 143 , 144 ] and with delamination and localized necrosis of the subchondral bone. The etiology remains unclear [ 28 , 29 , 31 ]. Repetitive microtrauma, such as that of overuse injury, is considered the significant factor leading to JOCD [ 28 , 29 , 145 ].

The most common site of JOCD is the medial femoral condyle, accounting for 85% of the cases [ 28 ]. The term “osteochondritis” suggests an inflammatory etiology: however, histology shows damage of the bone and cartilage with no inflammation [ 146 ]. Local bone vascular insufficiency is also postulated to contribute to JOCD [ 29 ].

Highly active athletes present with a history of aching and gradual onset of knee pain of several days to weeks duration, typically located over the anterior portion of the knee, worse during activity. There may be a history of intermittent knee effusion following a practice or game session [ 29 ].

The examination may reveal mild effusion or limitation of motion of the knee. Findings may also vary depending on the stage of the disease [ 147 ]. In the early stages, with the articular cartilage over the femoral condyle still intact, the signs are non-specific. In the later stages, when the articular cartilage is eroded, the fragment may separate and become an intra-articular loose body. This can cause pain, effusion, and locking. Typically, in lesions, the medial femoral condyle when the athlete flexes and internally rotates the leg, from full extension to about 30°, pain is elicited and is relieved upon external rotation [ 28 , 29 ].

Radiographic examination, with comparison with the other knee, is indicated when JOCD is suspected. In addition to the anteroposterior (AP) and lateral views, a tunnel view is useful to better identify the lesion, which appears as a well-demarcated radiolucent area [ 29 , 31 ]. In those who demonstrate significant edema, a hemarthrosis or discomfort, and inability to bear weight without pain, an MRI is often obtained. An MRI can be helpful in identifying unstable lesions [ 31 ].

Suzue et al. [ 148 ] investigated the prevalence of JOCD in children and adolescent soccer players using a questionnaire, distributed to 1162 players. Of these, 547 patients experienced pain in the legs or lumbar spine. Radiographic or ultrasonographic examination was performed in 106 players, and 80 (75.5%) were diagnosed JOCD. In conclusion, the majority of players who had experienced pain and were found to have osteochondritis had severe injuries such as JOCD or lumbar spondylolysis [ 148 ].

Early diagnosis followed by restriction of activities and symptomatic treatment of pain generally allows for healing of lesions over a period of 8–12 weeks [ 30 , 31 , 149 ]. Spontaneous healing of the lesion is the usual outcome in children and adolescents with open distal femoral physis. Prognosis is excellent in younger patients [ 149 ].

Treatment is based on the stability of the lesion and the status of the overlying cartilage. The lesion may be unstable or loose, and these cases as well as in those athletes with large effusions or with marked symptoms which do not improve with conservative care may go to surgery for drilling, reattachment, or excision of the osteochondral lesion [ 31 ].

Overuse injuries can affect the muscle, tendon, and bone. Tendon injuries give rise to substantial morbidity, and current understanding of the mechanisms involved in tendon injury and repair is limited. Tendon physiology and structure may include ROS involvement in various aspects of the predisposition to and participation in the degenerative process and subsequent response to injury. Bone can be damaged by repeated microtrauma and overuse. Stress reaction and stress fractures are very common in athletes, and the treatment consists in the treatment of the risk factors. Further research is required to improve our knowledge of tendon and bone healing. This will enable specific treatment strategies to be developed.

Abbreviations

Anteroposterior

Achilles tendinopathy

Bone mineral density

Food and Drug Administration

High-volume image-guided injections

Interleukin

Juvenile osteochondritis dissecans

Low-intensity pulsed ultrasound

Monocyte chemoattractant protein

Programed cell death

Pulsed electromagnetic fields

Platelet-rich plasma

Royal London Hospital

Reactive nitrogen species

Reactive oxygen species

Tumor necrosis factor

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Two medical doctors (RA and DT) performed the search of articles in the available scientific literature, while the researcher with more experience (NM) solved cases of doubt. At the beginning of the procedure, each examiner read the abstracts of all articles and selected the relevant ones. After 1 week, the same studies were read again to establish the agreement of the researchers on the selection. Each author has contributed to writing the manuscript. All authors read and approved the final manuscript.

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Aicale, R., Tarantino, D. & Maffulli, N. Overuse injuries in sport: a comprehensive overview. J Orthop Surg Res 13 , 309 (2018). https://doi.org/10.1186/s13018-018-1017-5

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  • Stress fracture
  • Overuse injuries
  • Osteochondritis dissecans
  • Tendinopathy

Journal of Orthopaedic Surgery and Research

ISSN: 1749-799X

sports injury research paper

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Interdisciplinary sport injury research and the integration of qualitative and quantitative data

  • S.E Hausken-Sutter 1 ,
  • K Boije af Gennäs 2 ,
  • A Schubring 1 , 3 ,
  • J Jungmalm 1 &
  • N Barker-Ruchti 1 , 4  

BMC Medical Research Methodology volume  23 , Article number:  110 ( 2023 ) Cite this article

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To understand and prevent sport injuries, scholars have employed different scientific approaches and research methods. Traditionally, this research has been monodisciplinary, relying on one subdiscipline of sport science and applying qualitative or quantitative research methods. Recently, scholars have argued that traditional approaches fail to address contextual components of sport and the nonlinear interactions between different aspects in and around the athlete, and, as a way forward, called for alternative approaches to sport injury research. Discussion of alternative approaches are today taking place, however, practical examples that demonstrate what such approaches entails are rare. Therefore, the purpose of this paper is to draw on an interdisciplinary research approach to (1) outline an interdisciplinary case analysis procedure (ICAP); and (2) provide an example for future interdisciplinary sport injury research.

We adopt an established definition and application of interdisciplinary research to develop and pilot the ICAP for interdisciplinary sport injury teams aiming to integrate qualitative and quantitative sport injury data. The development and piloting of ICAP was possible by drawing on work conducted in the interdisciplinary research project “Injury-free children and adolescents: Towards better practice in Swedish football” (the FIT project).

The ICAP guides interdisciplinary sport injury teams through three stages: 1. Create a more comprehensive understanding of sport injury aetiology by drawing on existing knowledge from multiple scientific perspectives; 2. Collate analysed qualitative and quantitative sport injury data into a multilevel data catalogue; and 3. Engage in an integrated discussion of the collated data in the interdisciplinary research team.

The ICAP is a practical example of how an interdisciplinary team of sport injury scholars can approach the complex problem of sport injury aetiology and work to integrate qualitative and quantitative data through three stages. The ICAP is a step towards overcoming the obstacles of integrating qualitative and quantitative methods and data that scholars have identified.

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Introduction

Traditionally, sport injury researchers study injury aetiology in youth athletes from the perspective of one scientific discipline (e.g., exercise physiology, biomechanics; sport psychology; sport sociology). Broadly speaking, researchers of these disciplines follow distinctive assumptions of what an injury is and what research questions, ethical stances, research methods and interpretations and explanations of results are most appropriate to researching injury aetiology in youth athletes [ 1 , 2 , 3 ]. Biomedical scholars, for instance, often regard an injury to be related to identifiable individual physical factors and apply quantitative methods to test if components such as muscle strength previous injury, and growth and maturation are related to injury aetiology [ 4 , 5 , 6 ]. Sport sociologists often understand sport injury as a socially constructed phenomenon and apply qualitative methods to interview youth athletes about the coach-athlete relationship and/or observe contextual aspects such as the training environment [ 7 , 8 ]. To study aspects such as injury experiences, consequences and perceptions, sport psychology researchers oftentimes use either quantitative [ 9 ], qualitative [ 10 ] or mix qualitative and quantitative methods [ 11 ].

The predominant monodisciplinary approach to sport injury research has provided extensive knowledge on injury aetiology in youth athletes. In recent years, however, several sport injury scholars have critiqued the traditional monodisciplinary approach and suggested a turn to complexity approaches to account for the multifaceted nature of sport injury aetiology [ 12 , 13 , 14 , 15 , 16 , 17 ]. The key argument is that contemporary research has not been accounting for the nonlinear interactions between different components across different dimensions, such as interactions between people and the physical and social environments, and thus, does not consider the unpredictable, fluid, and flux nature of sport injuries. Instead, the scholars suggest a framework away from risk factors towards identifying risk patterns and looking deeper into the complex nature of sport injury aetiology [ 12 , 13 , 15 , 16 , 17 ]. To achieve this goal, however, scholars consider how to best address complexity differently, and best practice examples are a work in progress for sport injury research. To address this gap and to contribute to the current discussion on alternative approaches we propose that interdisciplinarity offers potential. We have adapted and applied the definition of interdisciplinarity based on Julie Klein and William H. Newell [ 18 ], who have significantly influenced the field of interdisciplinary research in the past 40 years. These scholars define interdisciplinarity as a research process that addresses a complex phenomenon that cannot be dealt with adequately by a single scientific discipline. To fit Klein and Newell’s definition to the team context within which we conducted interdisciplinary research, we adapted Klein and Newell’s [ 18 ] definition which in this article involves collaboration of researchers specialising in different scientific disciplines and methodological approaches, and the application of both qualitative and quantitative methods.

The need for interdisciplinarity in sport injury research was first called for by Burwitz et al. [ 19 ] in the 1990s. Since then, several sport science scholars have argued that research on athlete health and wellbeing requires a holistic and multidimensional approach, where scholars from different disciplines collaborate [ 20 , 21 , 22 ]. The rationale is that different scientific perspectives and research methods have established important insight into sport injury aetiology and can thus address a greater range of components that influence sport injury aetiology. The different disciplinary insights offer a means to facilitate an integrated understanding and discussion of sport injuries in relation to individual players’ context and situation, which has the potential to extend existing insights [ 19 , 22 , 23 ]. For example, and as demonstrated by sport science scholars Schofield, Thorpe, and Sims [ 24 ], their bringing of qualitative sociological data into dialogue with quantitative physiological data helped the team to draw novel conclusions as to which athletes were struggling with health problems, which eventually led to new insight and a return to the empirical data for a second stage of analysis. Such new and integrated insight into athlete health is necessary to develop prevention strategies that are more effective in addressing the components of sport injury aetiology. To that end, this paper contributes with a piloted procedure on how to work in an interdisciplinary team with qualitative and quantitative data in sport injury research. Specifically, the purpose of this paper is to draw on an interdisciplinary research approach to (1). outline an interdisciplinary case analysis procedure (ICAP); and (2). provide an example for future interdisciplinary sport injury research.

Interdisciplinary research and implications for data analysis

Interdisciplinary scholars Klein and Newell [ 18 ] define interdisciplinary research as:

a process of answering a question, solving a problem, or addressing a topic that is too broad or complex to be dealt with adequately by a single discipline or profession … [interdisciplinary research] draws on disciplinary perspectives and integrates their insights through construction of a more comprehensive perspective [ 18 p3].

Interdisciplinarity thus constitutes both a research approach and a process that is developed for the study of complex systems [ 23 ]. A key aspect of interdisciplinary research is integration: “…crafting an integrated synthesis of the separate parts that provide a larger, more holistic understanding of the question, problem or issue at hand” [ 18  p12; emphasis in original]. Detailing this definition, interdisciplinarians Repko, Szostak and Buchberger [ 25 ] outline that integration is a cognitive process, where the researcher(s) evaluate disciplinary knowledge from multiple scientific perspectives and create a more comprehensive understanding of the problem under study based on the disciplinary knowledge. The common ground is, according to several interdisciplinary scholars, necessary for integration of disciplinary insight to be possible [ 25 , 26 ]. For interdisciplinary sport injury research, we took this to mean that a team of disciplinarians, could collaborate, share, and integrate disciplinary knowledge, and engage in a discussion during which qualitative and quantitative data could be integrated.

The interdisciplinary research approach outlined above may seem familiar to scholars conducting mixed methods research in, for example, health research and sport psychology [ 27 , 28 ]. Mixed methods research does indeed often aim to integrate qualitative and quantitative methods and data to gain broad and deep understanding and to generate unique insight into multifaceted phenomena [ 27 , 29 , 30 ]. However, the type of interdisciplinarity proposed in this paper differs from the mixed methods research approach by involving strategies for dealing with an array of ontological, epistemological, and contextual challenges that often exist or emerge when a team of disciplinarians collaborate. For example, interdisciplinary teams in sport science research can experience, and have experienced problematic power relationships, language barriers, and misunderstandings that complicate the integration of qualitative and quantitative data if these issues are not dealt with in the team [ 22 , 24 , 31 ]. Such teamwork and related onto-epistemological differences have received sparse attention in mixed methods research [ 32 , 33 , 34 ]. Therefore, to account for these differences, interdisciplinarity does not only involve strategies for integrating methods and data, but also for integrating disciplinary knowledge to create a more comprehensive understanding of the problem under study, which is necessary for integration to be successful [ 26 ].

With the potential and challenges of interdisciplinary research in mind, how can qualitative and quantitative data be integrated in an interdisciplinary research team context? As we could not locate established procedures for interdisciplinarity in sport science and sport injury research, we draw on suggestions of an applied interdisciplinary process developed by Newell and colleagues [ 26 , 35 ], which constitutes integrative steps to guide researchers through the decisions made in the interdisciplinary process. According to these scholars, integration cannot follow an algorithm; rather, integration requires analytical reasoning and creative thinking as the interdisciplinary research process and its steps are iterative and complex [ 26 , 35 ]. Moreover, being humble, respectful of, and acknowledging each other’s perspectives has been recognised as valuable cognitive skills when aiming to integrate knowledge and data across disciplinary borders [ 22 , 36 ]. To successfully conduct integrated research, then, efforts beyond those associated with conducting high-quality disciplinary research and mixed methods approaches are necessary [ 26 ]. First, researchers need to understand a problem from different perspectives and disciplines. Second, researchers need to consider different disciplinary views and the methodological toolkits that the disciplines constitute. Finally, it is important that researchers embrace a holistic approach – an understanding of how disciplinary ideas and information relate to a problem and to each other. In sum, as the holistic thinking involved in interdisciplinary research opposes the traditional reductionist disciplinary strategy, interdisciplinary research is not “business as usual” [ 26 p262].

To develop an interdisciplinary case analysis procedure, which became the ICAP, we draw on research conducted in the interdisciplinary research project “Injury-free children and adolescents: Towards better practice in Swedish football (the FIT project) [ 37 ]. The purpose of the FIT project was to provide evidence-based interdisciplinary injury prevention strategies. The project aimed to produce a comprehensive and integrated picture of injury aetiology in a sample of male and female Swedish football players aged 10 to 19. The research team consisted of scholars from four scientific disciplines—biomechanics, sport medicine, sport sociology, and sport coaching. Based on the four scholars’ respective scientific expertise, qualitative data was generated through interview and observation-studies and quantitative data through biomedical measurements (kinematics/movement; strength; joint range of motion/flexibility; Peak Height Velocity (PHV)) and a longitudinal questionnaire study implementing an adapted version of the OSTRC-H questionnaire [ 38 ]. Upon completion of the studies, qualitative and quantitative data were analysed according to their respective disciplinary data analysis methods and quality standards (e.g., thematic analysis for qualitative interview and observation-data; statistical procedures for biomedical data). The next step was to perform integrated data analysis, which led us to the development of the ICAP.

The Interdisciplinary Case Analysis Procedure (ICAP)

The ICAP is a flexible, circular, and iterative procedure entailing three stages (see Fig.  1 ). The stages reflect the research process of a team of disciplinary researchers aiming to integrate data through an interdisciplinary data analysis procedure. In stage 1 and taking seriously the need for integration of disciplinary insights early in the research process, the aim is to create a comprehensive understanding of the phenomenon/a that the project team aims to study based on the scientific disciplines included in a project. In stage 2, qualitative and quantitative data, analysed according to their respective disciplinary standards, are brought together. Finally, in stage 3, the collated data is discussed through a team meeting consisting of the researchers representing the data included in step 2.

figure 1

The three stages of the Interdisciplinary Case Analysis Procedure (ICAP)

Stage 1: Creation of comprehensive understanding

In stage 1, the aim is to create a comprehensive understanding of the problem that the project team intends to study based on the scientific disciplines included in the project [ 23 ]. To create comprehensive understanding, it is necessary that the team members find a common language, recognise conflicts and their unique strengths, and the disciplinary knowledge each member brings to the study [ 23 ]. In this stage, the either/or disciplinary thinking is replaced by both/and thinking requiring the disciplinarians to “think outside of the box” [ 26  p260].

For the FIT project to create comprehensive understanding of sport injury, we held several team meetings to discuss and reflect upon our different research approaches and understandings of sport injury aetiology. The meetings were carefully planned and led by the project leader, who aimed to be inclusive in type of language and making room for all disciplinary perspectives. We also reviewed diverse disciplinary literature relevant to sport injury, with a particular focus on youth football, to critically reflect upon onto-epistemological differences in sport injury research for the narrative review article we published together [ 39 ]. Through reviewing literature, we also considered the basic assumptions of complexity thinking, especially in relation to nonlinear interactions between different components in the athlete’s context. Moreover, the project was presented within and outside of academia to gain additional knowledge on disciplinary research approaches and sport injury aetiology in youth athletes. The planning and implementation of the FIT project’s four sub-studies also taught us more about the differences in qualitative and quantitative methods in relation to concepts such as recruitment, validity, and reliability. Finally, all researchers had the opportunity to participate in the respective studies, where, for example, the sport coaching researchers participated in the biomedical testing.

Stage 2: Collation of qualitative and quantitative data

The aim of Stage 2 is to bring together qualitative and quantitative data in preparation for stage 3’s integrated discussion of injury aetiology.

For the FIT project, we focused on one single case of a female player aged 14 that had participated in all four studies included in the FIT project. This entailed two steps: First, individual analysis of the different datasets using suitable data analysis methods (i.e., thematic analysis for qualitative interview and observation-data; statistical procedures for biomedical data). Second, collation of the analysed data per research participant in a multilevel data catalogue in the form of an Excel document (see supplemental online file ). The idea of this catalogue is to visualise and collate in a common “space” qualitative and quantitative data to provide a foundation for the integrated discussion in stage 3. The multilevel data catalogue entails six levels of information (see Table 1 for a simplified overview; for a more comprehensive description of the six levels, see the supplementary file ).

In level 1, to demonstrate the FIT project’s disciplinary perspectives, the multilevel data catalogue is divided into one biomedical (biomechanics, sport medicine) and one sociological (sociology, sport coaching) section. The purpose of level 2 is to show the different types of measurement and research methods employed under each disciplinary perspective. The columns in level 2 are divided into different biomedical- and sociology-themes (e.g., strength measurements; observation, interview). Level 3 specifies the type of data measured and generated for each of the themes. For example, for the strength theme, the hip abduction/adduction ratio is listed in separate columns. For the interview theme, topics such as “knowledge about injury and injury prevention” are listed. Level 4 contains data excerpts to demonstrate the type of qualitative and quantitative data from the individual analyses of the injured football player. Quantitative data is represented in numeric form (for example results from the strength measurements) while qualitative data is represented in textual form (for example quotes from the interview). Level 5 shows the reference value for qualitative and quantitative data. For the former, codes were given through a qualitative thematic analysis procedure [ 41 ]. For the latter, individual biomedical data was calculated and compared to the mean values of one reference group “females aged 14–19”. Finally, level 6 contains interpretation and evaluation of the qualitative and quantitative data in relation to reference values and literature. This level lays the most important groundwork for the team discussion and continuation of data integration for stage 3.

Stage 3: Team meeting and discussion

In stage 3, the aim is for the researchers from the different disciplines included in the interdisciplinary project to meet and discuss the collated qualitative and quantitative data. According to Newell [ 26 p261], the goal of this interdisciplinary stage is to “achieve a balance among disciplinary influences on the more comprehensive understanding”, i.e., no disciplinary perspective should dominate the discussion. The qualitative and quantitative data about the complex problem (i.e., sport injury) is in this stage examined to “identify patterns of behaviour” [ 26 p261], or relationships (interactions) between different components in the system that influence injury aetiology.

For the FIT project, stage 3 was conducted through a team meeting consisting of researchers representing the scientific disciplines included in the project. The discussion was moderated by one of the researchers in the team, who had experience from the FIT project’s four sub-studies and knowledge of interdisciplinary research. The data catalogue containing analysed data served as the basis for the two-step discussion: First, each researcher presented interpretations of the analysis of data relevant to their disciplinary expertise. Their interpretations were related to the FIT project’s overarching aim and were not yet specific to a specific case/research participant. During each researcher’s statement of the analysed data, the other team members were invited to ask questions, which is argued to enable a deeper understanding of the problem at hand [ 42 ]. Second the different perspectives and data were related to the 14-year-old female player’s injury in a joint discussion. The integrated discussion was also a way to identify different patterns in the empirical data.

Implications for interdisciplinary injury data analysis

As part of the process of developing and piloting the ICAP, we have encountered four issues that have implications for the use of the procedure and future research.

First, to facilitate the collation of qualitative and quantitative sport injury data in interdisciplinary research, we experienced that the different assumptions regarding disciplinary perspectives and qualitative and quantitative data require consideration early in the interdisciplinary research process. We propose that this consideration is vital as underlying ontological, epistemological, and methodological assumptions can complicate interdisciplinary research and integration due to misunderstandings and difficulties in reflecting and verbalizing these assumptions among members of interdisciplinary research teams. Therefore, the ICAP was, and needs to be part of a purpose-driven interdisciplinary research process that focuses on integration of disciplinary perspectives and research methods already in the planning and designing-phase of a project.

Second, as differences in assumptions influence how researchers define and research a phenomenon, it is necessary to facilitate collation through three circular, iterative, and pragmatic stages that enable teamwork across disciplinary borders. Indeed, working interdisciplinarily requires spaces, or “a community of research practice” [ 3 p56] within and through which the team can explore, negotiate, and reflect upon their commonalities and differences in scientific perspectives [ 43 ]. We have therefore found that it was of great importance that the team followed a procedure through which we met on a regular basis and had a team leader that supported methodological flexibility throughout the process. Such regular team meetings have indeed been found to facilitate the development of strategies that can help bring qualitative and quantitative materials together [ 24 ]. Following such a procedure does not, however, mean that working interdisciplinary is a strict and linear process. On the contrary, we did, for example, experience that we had to go back to stage 1 and learn more about concepts such as reliability, validity, credibility, generalisability, and transferability in relation to qualitative and quantitative methods [ 44 ] when interpreting the data in stage 3.

Third, and to further facilitate collation of qualitative and quantitative data in an interdisciplinary research team context, we noticed that the team benefitted from including a researcher with knowledge of interdisciplinary research and the different disciplines included in the project. We found this particularly important in stage 3 of the ICAP, when the team discussed the compiled data in relation to the injured player. When the discussion reached a dead-end, or when the disciplinarians misunderstood each other or the data, the interdisciplinary researcher moderator could clear up misunderstandings by, for example, pointing out how the different disciplines understand and interpret concepts differently and helping the team to find a common language. It occurs, for instance that qualitative and quantitative data contradict, which can be seen as a problem and an obstacle for integration [ 31 ]. Including an interdisciplinarian in the integration phase can, however, help the team use the contradictions in data to create new insight into the problem under study [ 31 ], which is key in Newell’s interdisciplinary process [ 26 ]. The idea of the interdisciplinarian , [ 26 ] or interlocutor , [ 30 ] as someone in the middle, who takes part in dialogue and conversation with the disciplinarians, can help the team see beyond their disciplinary borders, create unity, and refocus the team’s efforts towards constructive engagement in knowledge production [ 43 ]. Although the interdisciplinarian might not be able to eliminate possible power inequalities between the disciplinarians, paying attention to these boundaries and engaging the team in conversation can facilitate a common and interdisciplinary understanding of sport injury aetiology. For the FIT project, the interdisciplinarian helped the team to establish several aspects that needed further development, such as a need for a larger quantitative data set to be able to finalise the quantitative analysis as well as a need for additional cases to find patterns between cases. The team also realised the need for discussing the qualitative data in relation to findings and interpretations from similar qualitative research.

Fourth, we have noticed that successful integration requires a common understanding of what integration means in the team and where in the research process integration should take place. For the FIT project, integration involved a comprehensive understanding of sport injury aetiology in stage 1 [ 39 ], the collation of qualitative and quantitative data in one common space in stage 2 (the multilevel data catalogue), and an integrated discussion in stage 3 which together facilitated our interdisciplinary understanding of sport injury aetiology. There are, however, differences in degrees of integration [ 45 ]. Sometimes, for example, integration of knowledge and the collaborative process includes actors outside of academia and can lead to the creation of a new framework, which can generate a fundamental epistemological shift [ 36 , 43 ]. Being clear in the beginning of a project on what, when, and how to integrate is key for sucessful collaboration across disciplinary boarders.

Finally, some methodological limitations need to be considered before conducting an integrated analysis procedure such as the ICAP. First, the ICAP is a complex procedure to carry out and requires more time, resources, and expertise than traditional analysis procedures. Second, there is a lack of research on the integration of qualitative and quantitative data in the interdisciplinary research context, and more research is needed on the integrated potential of such an approach and process. Finally, in the interest of better understanding the complexity of sport injury aetiology, there is a need to explore the pragmatic negotiations that an interdisciplinary research team needs to make when integrating seemingly opposing worldviews, methods, and data.

The purpose of this paper was to draw on an interdisciplinary research approach to (1) outline an interdisciplinary case analysis procedure (ICAP); and (2) provide an example for future interdisciplinary sport injury research. The Interdisciplinary Case Analysis Procedure (ICAP) consists of a three-stage process that allowed us to create a more comprehensive understanding of sport injury aetiology, collate qualitative and quantitative data in a multilevel data catalogue and engage in an integrated discussion to identify patterns in the empirical data. Working interdisciplinarity is not business as usual and requires researchers to adopt certain cognitive skills that might be outside of their disciplinary comfort-zone. Creativity, flexibility, and openness are key such skills.

While we have developed the ICAP specifically for an interdisciplinary youth sport injury research project, the procedure is generic and can be applied in interdisciplinary research addressing other complex phenomena. For researchers who aim to adopt (and adapt) the ICAP, it is important to keep in mind that the procedure is not “just” about mixing or integrating qualitative and quantitative data, it includes strategies to integrate disciplinary knowledge and consider onto-epistemological differences throughout the whole research process. In so doing, the ICAP is a step towards overcoming the obstacles of integrating qualitative and quantitative methods and data that scholars have identified. It is our hope that sport science and other researchers will consider and apply ICAP in the interest of better understanding the complexities of a phenomenon under study.

Availability of data and materials

The datasets used and analysed during the current study are available from the corresponding author on reasonable request.

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Open access funding provided by University of Gothenburg. The Swedish Research Council for Sport Science (CIF) has been funding the FIT project since 2016 through partial funding of a PhD studentship (F2016-0017; FO2021-0016; FO2017-0004; FO2018-0007; FO2020-0005; FO2021-0016) and partial project funding for one year (P2017-0090). The FIT project application was developed for a specific 2014 CIF call for interdisciplinary research on health and performance in child and adolescent sport. CIF funds research in the field of sports, which are defined to include everything from club sports to exercise, physical activity, performance and training for children, young people, adults, and the elderly.

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S.E Hausken-Sutter, A Schubring, S Grau, J Jungmalm & N Barker-Ruchti

Department of Sport Science, Malmö University, Malmö, Sweden

K Boije af Gennäs

Institute of Sociology and Gender Studies, German Sport University Cologne, Cologne, Germany

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School of Health Sciences, Örebro University, Örebro, Sweden

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Contributions

NBR initiated and designed the FIT project with SG. SEHS and NBR led the drafting of the manuscript. All authors collected and analysed the data. KBaG, AS, SG, JJ and NBR contributed to the writing of the manuscript. All authors read and revised the manuscript. All authors read and approved the final manuscript.

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Hausken-Sutter, S., Boije af Gennäs, K., Schubring, A. et al. Interdisciplinary sport injury research and the integration of qualitative and quantitative data. BMC Med Res Methodol 23 , 110 (2023). https://doi.org/10.1186/s12874-023-01929-1

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Sports Injury Research

Sports Injury Research

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With the increasing focus on tackling obesity and other lifestyle-related illnesses and conditions, participation in sports and physical activity is growing. The consequences are that injuries and unwanted side-effects of healthy activity are becoming major health problems. Prevention is crucial to health gain, both in the short-term (preventing immediate injury), and in the longer term (reducing the risk of recurrence and prolonged periods of impairment). Prevention follows four main steps: 1) the sports injury problem must be described in incidence and severity; 2) the etiological risk factors and mechanisms underlying the occurrence of injury are identified; 3) preventive methods that are likely to work can be developed and introduced; and 4) the effectiveness and cost-effectiveness of such measures are evaluated.

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  • Orthop J Sports Med
  • v.8(6); 2020 Jun

Risk of Injuries Associated With Sport Specialization and Intense Training Patterns in Young Athletes: A Longitudinal Clinical Case-Control Study

Neeru jayanthi.

† Departments of Orthopaedics and Family and Preventive Medicine, Emory University School of Medicine, Atlanta, Georgia, USA.

‡ Emory Sports Medicine Center, Johns Creek, Georgia, USA.

Stephanie Kleithermes

§ Department of Orthopedics and Rehabilitation, University of Wisconsin School of Medicine and Public Health, Madison, Wisconsin, USA.

∥ Parkinson School of Health Sciences and Public Health, Loyola University Chicago, Chicago, Illinois, USA.

Jacqueline Pasulka

¶ Department of Pediatrics, University of Chicago, Chicago, Illinois, USA.

# Stritch School of Medicine, Loyola University Chicago, Maywood, Illinois, USA.

Cynthia LaBella

** Institute for Sports Medicine, Ann & Robert H. Lurie Children’s Hospital of Chicago, Chicago, Illinois, USA.

†† Department of Pediatrics, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA.

Background:

There are no clinical longitudinal studies exploring the associations between sport specialization and intense training patterns and injuries in young athletes.

To prospectively determine the relationship between young athletes’ degree of sport specialization and their risk of injuries and reinjuries.

Study Design:

Case-control study; Level of evidence, 2.

Young athletes aged between 7 and 18 years presenting for sports-related injuries or sports physical examinations were recruited from either sports medicine clinics or pediatric/family medicine offices. Each participant completed a baseline survey at enrollment and an identical follow-up survey every 6 months for 3 years. Surveys assessed training patterns and injuries. Injury type (acute, overuse, or serious overuse) and clinical diagnosis were also recorded from electronic medical records.

Of the 1208 participants who provided consent, 579 (48%) completed the baseline survey and first follow-up survey at 6 months (mean age, 14.1 ± 2.3 years; 53% female). Of this sample, 27% (158/579) of participants were uninjured, and 73% (421/579) were injured, with 29% (121/421) of injuries classified as reinjuries. Consistent with previous studies, over the 3-year study period, the degree of sport specialization had an effect such that more specialized athletes were significantly more likely to be injured ( P = .03) or have an overuse injury ( P = .02) compared with less specialized athletes after adjusting for potential confounders. Additionally, female athletes were more at risk for all injuries ( P = .01) and overuse injuries ( P = .02) after adjusting for covariates. Finally, young athletes who trained in weekly hours in excess of their age or who trained twice as many hours as their free play were significantly more likely to be injured on univariate analysis (both P < .001).

Conclusion:

Our study confirms that over time, young athletes, and in particular young female athletes, were more likely to be injured and sustain an overuse injury if they had a higher degree of sport specialization. Similarly, those athletes whose training hours exceeded thair age or whose sports hours exceeded their free play by a factor of greater than 2 were also more likely to develop injuries and overuse injuries.

Increasingly, children and adolescents are focusing and training year round in a single primary sport and at an early age. 16 These behaviors are in conflict with current recommendations for young athletes, which suggest participating in multiple sports and only specializing after middle adolescence or later. 2 , 4 , 8 , 11 , 13 , 19 These recommendations address numerous issues of concern among specialized athletes, including burnout or physical consequences such as injuries and overuse injuries. 3 , 7 , 8 , 21 , 22 , 27 – 29 Only recently have the independent effects of sport specialization and intense training patterns on injury risk in young athletes been documented. 1 , 10 , 13 We had previously demonstrated a cross-sectional association between single-sport specialization and a history of injuries in competitive Midwestern junior tennis players. 12 However, these data did not include other sports or specific clinical diagnoses. In a clinical case-control cohort study, we also demonstrated an independent risk of injuries, overuse injuries, and serious overuse injuries related to the degree of specialization when controlling for age and volume of training. 15 These findings have been reproduced in other nonclinical cross-sectional populations, particularly as they pertain to the overuse injury risk and degree of sport specialization. 1 , 10 , 20 , 25

In an effort to use our data to inform clinical recommendations for young athletes, we investigated the total number of hours per week spent in organized sports training in relation to the athlete’s age. 15 Based on our previously published data, athletes who trained for their sport more hours per week than their chronological age had a greater risk of serious overuse injuries than those training fewer hours than their age (odds ratio [OR], 2.07) on multivariate analysis. 15 Some experts now recommend limiting weekly training hours to fewer than the athlete’s age to reduce the risk of injuries. 23 Additionally, a sports training ratio (weekly hours in organized sports/weekly hours in free play) was calculated based on reported weekly training hours to provide another clinical tool regarding the training risk and type of physical activity. We recommended that this ratio not exceed 2:1, as the OR of serious overuse injuries was 1.87 on multivariate analysis. 15

While preliminary cross-sectional studies have suggested a relationship between the degree of sport specialization and the injury risk, these studies could not infer causality because of the lack of a longitudinal evaluation. Furthermore, there have been limited prospective data regarding the reinjury risk in a population of young athletes in varying degrees of sport specialization. In this prospective clinical cohort study of youth athletes, we evaluated (1) the longitudinal and independent effects of sport specialization on the risk of injuries and overuse injuries, (2) the effect of sports training patterns on the risk of reinjuries and overuse injuries, and (3) the longitudinal and independent effects of sex and age beginning sport specialization on the injury risk. Our hypotheses were that there would be a positive relationship between the risk of overuse injuries and the degree of sport specialization, that high-volume training patterns would result in a greater risk of overuse injuries, and that specialization would increase the risk of reinjuries, particularly with young female athletes who specialize early.

Study Design and Participant Recruitment

This was a multicenter clinical prospective cohort study involving youth from Chicago, Illinois, USA. Children and adolescents with sports-related injuries were recruited from 1 of 2 university hospital–based primary care sports medicine clinics, and uninjured children were recruited from affiliated pediatric or family practice clinics during visits for preparticipation sports physical examinations or well-child care visits.

Children and adolescents who were aged 7 to 18 years and who participated in at least 1 organized sport during the year were invited to participate. Children and adolescents who did not participate in any organized sports were not invited to participate. Only data from those participants who completed the baseline survey and at least 1 follow-up survey were analyzed. Signed parental consent was obtained for each participant, and signed adolescent assent was obtained from participants aged ≥12 years. The institutional review boards of both respective institutions, Loyola University Medical Center and Ann & Robert H. Lurie Children’s Hospital of Chicago, approved this study.

Participant Characteristics

Each participant’s baseline height and weight were measured by a registered nursing staff member, medical assistant, athletic trainer, or research assistant at the time of enrollment. The body mass index (BMI) was calculated as kg/m 2 . Follow-up anthropometric measurements were obtained from the participant's electronic medical record (EMR) when available or by self-report for participants who responded to follow-up surveys and did not have a recent visit noted on the EMR.

All participants completed 2 surveys at enrollment: (1) current sport specialization (Appendix) and (2) self-assessment of pubertal maturation (Tanner stage). The Tanner stage as determined by self-assessment has been used previously; however, its reliability has been questioned. 5 , 26 The sport specialization survey included information regarding organized sports played throughout the year; hours per week in organized sports (training and competition), physical education (PE) class, and free play; sports enjoyment; and degree of sport specialization (see next section). Injured athletes also completed an injury survey to report injury mechanism, training before the injury, and whether the injury was new or recurrent. Additional injury information, such as physician diagnosis, acuity, and treatment, was obtained from the participant’s EMR when available. Injuries acquired outside of organized sports were not recorded. Participants were asked to fill out a new sport specialization survey and injury survey (if a new injury occurred in the interim) every 6 months for 3 years; they were contacted every 6 months by email with weekly reminders and then also by telephone if not responding to email. There were no incentives provided for the completion of surveys.

Sport Specialization

While there has not been a consistent definition for sport specialization, we used a previously published definition: “year-round intensive training in a single sport at the exclusion of other sports.” 13 Using this definition, we categorized the degree of sport specialization as low, moderate, or high based on the participant’s answers to 3 survey questions: (1) Can you pick a main sport (ie, single-sport training)? (2) Did you quit other sports to focus on a main sport (ie, exclusion of other sports)? (3) Do you train more than 8 months in a year (ie, year-round training)? The number of “yes” answers to these 3 questions was used to assign a degree of specialization: 3 positive responses was categorized as highly specialized, 2 as moderately specialized, and ≤1 as low specialization. This approach to utilizing a degree of specialization was shown to be more reliable than using a binary definition in a population of high school athletes. 16 Because many organizations are interested in developing an age of specialization recommendation, we also considered an expanded definition of sport specialization by adding a fourth element: Did the athlete specialize (quit all other sports) under the age of 12 years? The scoring classification was the same as the original definition, except that if the answer was “yes” to all 4 questions, athletes were classified as extremely specialized.

Injury Characteristics

Injuries were classified using the clinical diagnoses obtained from the participant’s EMR and injury mechanism (acute, overuse, or serious overuse) when available. Acute injuries were defined as those diagnoses that could be related to a single traumatic event, while overuse injuries were defined as those diagnoses that could be attributed to a gradual onset unrelated to a specific traumatic event. Overuse injuries were further categorized as “serious overuse” if the physician-recommended treatment typically required at least 1 month of rest from sports. Serious overuse injuries included spondylolysis, stress fractures to the spine or extremity, stress injuries involving the physes, elbow ligament overuse injuries, and osteochondritis dissecans.

A reinjury was defined using the participant’s response to the following question: Is the injury you are being asked to talk about (describe) a repeat of an old injury, or is it a new injury? Any injury for which the participant stated that the injury produced similar symptoms/same pain as an old injury was classified as a “reinjury.” Otherwise, if the participant described different symptoms/pain, it was classified as a “new injury.”

Statistical Analysis

All analyses were conducted using SAS Version 9.4 (SAS Institute). Descriptive statistics including means and distributions were used to summarize the characteristics of injured versus uninjured participants at baseline. Independent variables evaluated included age, sex, hours per week of organized sports, hours per week of recreational free play, hours per week of PE class, and degree of sport specialization. The primary outcomes were total injuries, overuse injuries, serious overuse injuries, and reinjuries. For continuous measures (eg, age, weight, BMI, and weekly hours of organized sports, free play, PE class, and total physical activity), we report means and standard deviations or medians and interquartile ranges as appropriate. Frequencies and proportions are reported for categorical variables.

Univariable and multivariable generalized estimating equations with an exchangeable correlation structure were used to identify the association between sport specialization (time-varying covariate) and the injury risk over time, after adjusting for potential confounders such as sex, age, BMI, and variables identifying sports participation volume. Pairwise interactions with sport specialization were assessed. Because of the lack of significance in the univariable models and small injury counts, multivariable models were not constructed for serious overuse injury and reinjury outcomes. Final multivariable models for all-cause injuries and overuse injuries were determined via a combination of backward stepwise procedures and Akaike information criterion model selection using potentially significant variables identified on univariable analysis. Adjusted ORs and 95% CIs are reported. Sensitivity analyses were additionally conducted using all available data through 1 and 2 years, respectively, to assess the potential impact of dropouts on the 3-year association between specialization and injuries.

Of 1208 participants who enrolled and provided consent at baseline, 629 were excluded because of no follow-up information, resulting in a final study sample of 579 (48%) participants who completed at least the baseline survey and first follow-up survey at 6 months. By the 18-month follow-up survey, 308 of the 579 (53%) participants remained in the study. At the 3-year mark, only 11% (61/579) completed the sports participation and injury survey ( Figure 1 ).

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Object name is 10.1177_2325967120922764-fig1.jpg

Survey responses.

At baseline, 421 (73%) participants were injured ( Table 1 ). The mean age at baseline was 14.05 ± 2.26 years, with injured participants being slightly older (14.41 ± 2.08 years) than uninjured participants (13.03 ± 2.46 years) ( P < .001). Additionally, participants injured at baseline participated in more organized sports hours per week ( P = .007), had a higher median ratio of organized sports to free play ( P = .002), were more likely to exceed 8 months per year of sports training ( P = .003), and were more likely to be highly specialized (31% injured vs 18% uninjured) ( P < .001). Because age, sports hours, and months of training were significant on univariable analysis, they were all considered in the multivariable analysis.

Participant Characteristics at Baseline a

a Data are shown as mean ± SD unless otherwise indicated. P values represent comparisons between the uninjured vs injured groups. Percentages may be taken from different subpopulation calculations based on overall cohort for each variable. BMI, body mass index; IQR, interquartile range; PE, physical education.

Injury Characteristics Over Time

Table 2 provides injury characteristics over the study period. At baseline, only 29% (121/421) of injuries were classified as reinjuries. However, a majority of injuries during the follow-up period were classified as reinjuries throughout the first 24 months (∼70%-80% through the first 24 months). Similarly, only 33% (157/475) of injuries reported during the follow-up period were new injuries. Of all injuries reported during the study (at baseline and during follow-up), 41% (368/896) were classified as overuse injuries (34%-53% at each time point). Serious overuse injuries accounted for 8% of all injuries and 19% of all overuse injuries. The most commonly injured body parts reported in the data set were the knee (n = 199 [22%]), ankle and foot (n = 161 [18%]), and low back (n = 128 [14%]).

Injury Characteristics Over Time a

a Data are shown as n (%).

b Percentages represent those of athletes enrolled at each time point who reported an injury.

c A total of 896 injuries were reported in 421 athletes over the entire study period.

Sport Specialization Patterns Over Time

It was expected that sport specialization would increase over time; however, no trend in sport specialization was detected using the original definition of specialization ( P = .11) ( Table 3 ). This may in part be because of large dropout rates after 18 months. High sport specialization reached its peak with 40% of participants during the 18-month follow-up survey, while low specialization was at its lowest with 37% at the same time point. Using the expanded definition of sport specialization (age <12 years), a test for trend identified an increase in the proportion of extreme specializers over the 3-year period and a decrease in low specializers ( P < .001); however, the rate of specialization stayed relatively consistent among the moderate and high specializers.

Degree of Sport Specialization Over Time a

b A Somers' D test over time was conducted.

Longitudinal Analysis of All-Cause Injuries and Reinjuries

On univariable analysis, female sex (OR, 1.28 [95% CI, 1.01-1.62]; P = .04), increasing chronological age (OR, 1.11 [95% CI, 1.05-1.17]; P < .001), higher BMI (OR, 1.04 [95% CI, 1.12-1.27]; P = .05), and increased weekly hours of physical activity (OR, 1.19 per 5 h/wk [95% CI, 1.02-1.05]; P < .001) and of organized sports (OR, 1.39 per 5 h/wk [95% CI, 1.27-1.52]; P < .001) all contributed to greater odds of injuries ( Table 4 ). Athletes who exceeded a ratio of 2:1 for weekly hours in organized sports to free play, those who spent more weekly hours in organized sports than their age, and those who spent more than 8 months per year in organized sports training had greater odds of all-cause injuries and overuse injuries during the study period (baseline and follow-up) compared with those who did not meet the criteria. Highly specialized athletes throughout the study period had 1.72 times greater odds of an injury than low specialized athletes (95% CI, 1.35-2.20) and 1.52 times greater odds of an injury than moderately specialized athletes (95% CI, 1.18-1.96). Although not statistically significant, there was a trend toward extremely specialized athletes (via the expanded definition of specialization) to have greater odds of injuries compared with low specialized athletes (OR, 1.29 [95% CI, 0.95-1.74]; P = .10). No association was detected between age at specialization and the injury risk ( P = .54). Moreover, no variables significantly increased the odds of a reinjury on univariable analysis.

Univariable ORs for Injury Status a

a Reference levels for categorical variables: specialization at age <12 y (no), weekly hours in ratio of organized sports to free play >2:1 (no), weekly organized sports hours exceeding age (no), exceeding 8 mo/y of sports training (no), Degree of sport specialization (low), expanded degree of sport specialization (low). BMI, body mass index; OR, odds ratio.

Multivariable analysis showed that after adjusting for sex, age, time from baseline, BMI, and weekly hours in organized sports, highly specialized athletes were 1.41 (95% CI, 1.06-1.87) times more likely to experience an injury than low specialized athletes ( P = .02) ( Table 5 ). Similarly, moderately specialized athletes had an increased risk of injuries compared with low specialized athletes (OR, 1.38 [95% CI, 1.04-1.84]). After controlling for sex, age, time, BMI, and degree of specialization, the odds of an injury increased by 31% (OR, 1.31 [95% CI, 1.19-1.44]) for every 5 hours per week of organized sports activity ( P < .001). Similar patterns were found using the expanded sport specialization definition, and results are reported in Appendix Table A1 .

Multivariable ORs for Injury Status a

a Reference levels for categorical variables: female sex (male), degree of sport specialization (low), weekly organized sports hours exceeding age (no). BMI, body mass index; OR, odds ratio.

Longitudinal Analysis of Overuse and Serious Overuse Injuries

Female sex (OR, 1.50 [95% CI, 1.14-1.99]; P = .004), increased weekly hours of physical activity (OR, 1.12 per 5 h/wk [95% CI, 1.05-1.20]; P = .001), and increased weekly hours of organized sports (OR, 1.24 per 5 h/wk [95% CI, 1.11-1.39]; P < .001) were associated with overuse injuries on univariable analysis ( Table 4 ). The lack of adherence to published recommendations was associated with increased odds of overuse injuries during the study period (>2:1 sports/free play ratio: P = .003; weekly sports hours greater than age: P < .001; >8 mo/y of sports training: P < .001). Higher levels of sport specialization were also associated with an increased risk of overuse injuries ( P < .001). Age at specialization ( P = .16), chronological age ( P = .77), and BMI ( P = .21) were not univariably associated with the risk of overuse injuries. No univariable associations were detected with serious overuse injuries during the study period.

The final multivariable model for overuse injuries consisted of the following variables: sex, time, BMI, total weekly hours of physical activity, weekly sports hours, exceeding the weekly hours of organized sports by the age recommendation, and degree of sport specialization ( Table 5 ). After controlling for all variables in the model, athletes categorized as highly specialized had 1.46 (95% CI, 1.04-2.04) times greater odds of an overuse injury than low specialized athletes ( P = .03). Athletes categorized as moderately specialized had 1.58 (95% CI, 1.13-2.20) times greater odds of an overuse injury than low specialized athletes ( P = .007). Additionally, female athletes had 1.43 (95% CI, 1.05-1.96) times greater odds of an overuse injury compared with male athletes ( P = .02). Similar patterns were found using the expanded sport specialization definition, and results are reported in Appendix Table A1 . The results of sensitivity analyses of 1- and 2-year follow-up were similar to the associations reported for 3-year follow-up ( Appendix Tables A2 and ​ andA3 A3 ).

Prospective studies have previously been performed to evaluate the association between sport specialization and injury risk. 18 , 20 However, we believe that this is the first clinical study to report the relationship between sport specialization and injury risk in a longitudinal sample of young athletes. Furthermore, we believe that it is the first study to report the reinjury risk in a clinical population of young athletes. While our data demonstrate an association between an increased injury risk (both all-cause and overuse) and higher levels of specialization, we could not confirm an association between reinjury risk and degree of sport specialization in our study.

Sport Specialization and Injury Risk

The longitudinal findings support our previous cross-sectional study conclusions that indicated an independent positive association between increased sport specialization and the risk of injuries. 15 While this association between the injury risk and sport specialization has been confirmed in other cross-sectional populations, 1 , 10 , 20 , 24 , 25 there is no known published longitudinal study confirming that increased sport specialization may be causal for injuries in a clinical population of young athletes. Indeed, our data confirm that there is an increase in the overuse injury risk with higher degrees of sport specialization longitudinally, although this association was not seen for acute injuries. Previously, McGuine et al 20 explored the injury risk related to the degree of specialization in a 2-year longitudinal study of high school athletes (mean age, 16.1 years). Their study used data reported from high school athletic trainers in a variety of sports and confirmed some of the relationships between degree of sport specialization and overuse injury risk seen in our original baseline data. 20 However, sport specialization selection may often occur before high school, and in the study by McGuine et al, the rates of sport specialization were not evaluated over time. The mean age of participants in the current study was 14.1 years, and we included athletes from a variety of settings as well as club sports and also included a clinical diagnosis by a physician.

In the current study, sport specialization continued to be a risk factor, independent of age and training volume, which supports the conclusion that sport specialization alone may increase the risk of injuries even with similar training volumes. Although data are limited, a number of position and policy statements from various organizations, such as the American Academy of Pediatrics, AOSSM, and American Medical Society for Sports Medicine, have supported the recommendation to delay or limit sport specialization in young athletes. 4 , 9 , 11 , 19 The consensus from most sports medicine organizations is to recommend against early sport specialization because of the risk of injuries, burnout, and long-term attrition and health consequences. 3 , 8 , 13 , 21 , 27 – 29 Therefore, we recommend that young athletes proceed with caution when choosing to specialize and that they understand the potential increased risk of injuries and particularly overuse injuries.

We did not find an association between sport specialization and reinjury risk ( P = .35) ( Table 4 ). However, we found that there were 896 injuries reported over the study period, with 49% of these being reinjuries (see Table 2). Overuse injuries constituted 41% of all injuries. It has previously been suggested that approximately 50% of young athletes’ injuries are overuse injuries. 9 This distribution of total injuries, reinjuries, and overuse injuries is generally consistent but is potentially associated with selection bias, as this was a clinical population primarily from sports medicine practices.

Training more hours per week than one’s age and exceeding a 2:1 sports training ratio (organized to free play) have previously been associated with an increased risk of overuse injuries. In this longitudinal follow-up study, there was a higher proportion of injured athletes who trained more hours per week than their age and who exceeded the 2:1 sports training ratio. Specifically, it appears that exceeding these volume recommendations may continue to be a risk for the development of overuse injuries. This suggests that a framework of including age-appropriate volume-based recommendations for young athletes may help to reduce the risk of overuse injuries. One strategy to address this may be increasing the amount of self-directed free play. Kliethermes et al 17 demonstrated in a randomized controlled trial that young athletes who received serial evidence-based counseling (that included these recommendations) demonstrated fewer injuries over the course of the study period of 9 months compared with those who did not receive such counseling. While this finding was not statistically significant, it may suggest that adherence to age-appropriate volume recommendations may modify the risk of injuries.

The sex differences in young athletes for overuse injuries have been previously reported. 23 In the current population of young athletes, 41% were identified as having overuse injuries, with female athletes more likely to report any injury and an overuse injury. Jayanthi and Dugas 14 previously reported that the likely main influence on overuse injury risk in specialized athletes was female sex. This is a novel consideration, as young female athletes have previously been demonstrated to have neuromuscular and genetic influences that significantly increase the risk of anterior cruciate ligament injuries. While biomechanical factors have not been adequately investigated in the setting of sport specialization, one potential explanation is that young female athletes have a greater risk of overuse injuries based on sports types (individual, technical) that involve higher rates of specialization, a small subset of repetitive movement patterns (eg, serving in volleyball), and early intense year-round training. A recent biomechanical analysis of young female athletes does suggest that there may be higher knee abduction forces in specialized athletes. 6 Further study is needed to elucidate other modifiable risk factors for overuse injuries in the young female athlete.

Age at Specialization

Our longitudinal univariable results also did not detect an association between age at specialization or specialization before the age of 12 years and the all-injury risk. However, statistically, there was a trend toward a protective effect on overuse injury risk when specializing at later ages. There were also no differences in injury risk based on age at specialization in a previous clinical study of young athletes (>12 vs 11.8 years). 15 There are still no studies to date that have clearly demonstrated injury risk as related to a specific age of sport specialization. This may be because the studies are often cross-sectional, with a variety of sports that might diminish the potential effects of a specific sport. Additionally, the Tanner developmental stage may potentially be a better indicator for injury risk, particularly during ages when there is rapid growth. In this study, young athletes with later median Tanner stages for male pubic (stage 3), female pubic (stage 3), and breast (stage 4) were more likely to be injured in the baseline sample ( P < .001 for all) (see Table 1 ); however, this did not persist in longitudinal analysis. Future studies may consider sport-specific populations evaluated longitudinally during adolescence and rapid growth periods to discern sport-specific age of specialization or development recommendations.

Sport Specialization Over Time

No prior study has evaluated the effects of sport specialization over time. We found that there were no significant differences for the distribution of sport specialization from baseline to 36 months ( P = .11). However, the overuse injury risk did increase with time, and the degree of sport specialization was related to injury risk over time. This may suggest that there is a relationship between the degree of specialization and the longitudinal injury risk. Because this relationship persisted even when adjusting for exposure, we feel that there may be an independent contribution of injury and overuse injury risk related to the degree of sport specialization over time. Naturally, as these participants age, they may be more likely to be more specialized; however, this may be balanced by some of the previously highly specialized young athletes also becoming more diversified over time.

Limitations

Because this study included a sample of clinical patients from 2 large Midwestern institutions, one should not overgeneralize the findings to a broad population or school-based environment. There were no financial or other incentives to remain in the study, so there was significant attrition in response rates after 2 years, and as a result, the longitudinal follow-up beyond 2 years was low, making it harder to make firm conclusions. Yet, sensitivity analyses of 1- and 2-year follow-up data ( see Appendix Tables A2 and ​ andA3) A3 ) suggest similar associations as those presented for 3-year follow-up. In addition, a majority of injuries during the follow-up period were classified as reinjuries throughout the first 24 months, which may have influenced injury type findings. The changes in sport specialization over time were captured only as a group variable and therefore do not necessarily reflect a participant’s change in sport specialization status. Additionally, we did not account for sports or sports type in the relationship of injuries to sport specialization. We recommend for this to be evaluated in sport-specific studies. Selection bias is expected, particularly in the follow-up sample, as sports medicine physicians included in the study primarily saw injured young athletes rather than healthy athletes. Those participants who were diagnosed with a sports injury in the clinic may have been more likely to follow up because they had an injury to report during the follow-up period.

This is the first study to report an association between the degree of sport specialization and the risk of injury in a clinical cohort of young athletes followed for 3 years. Highly specialized athletes, female athletes, and those who trained more hours per week than their age were more likely to develop injuries and overuse injuries, even when accounting for age and hours of week of training. Reinjury rates were approximately 50% over the study period, but there was no association between reinjury rate and volume of specialized training.

Acknowledgment

The authors acknowledge Noor Alawad, Katy Baumgartner, Archana Bokka, Daniel Fischer, Brittany Patrick, Courtney Pinkham, and Meghan Schmitt for their assistance in study planning and participant recruitment.

Sport Specialization Survey

Please check one box for each question , and answer all the questions to the best of your ability with the help of a parent.

1. _______________________ 2. _______________________ 3. _______________________

4. _______________________ 5. _______________________

□ 0 □ 1 □ 2 □ 3 □ 4 □ 5 □ 6

□ 0 □ 1 □ 2 □ 3 □ 4 □ 5 □ 6 □ 7 □ 8 □ 9 □ 10 □ 11 □ 12 □ 13 □ 14 □ 15 □ 16 □ 17 □ 18 □ 19 □ 20

(if more than 20, please write the number of hours) ______

□ 1 □ 2 □ 3 □ 4 □ 5 □ 6 □ 7 □ 8 □ 9 □ 10 □ 11 □ 12 □ 13 □ 14 □ 15 □ 16 □ 17 □ 18 □ 19 □ 20

□ 3 □ 4 □ 5 □ 6 □ 7 □ 8 □ 9 □ 10 □ 11 □ 12 □ 13 □ 14 □ 15 □ 16 □ 17 □ 18

□ Yes □ No

□ Agree □ Disagree

  • If yes, please name the sport __________________

PLEASE ONLY ANSWER QUESTIONS 10 & 11 IF YOU HAVE ONE SPORT THAT IS MORE IMPORTANT THAN ANY OTHER.

□ 1 □ 2 □ 3 □ 4 □ 5 □ 6 □ 7 □ 8 □ 9 □ 10 □ 11 □ 12

An external file that holds a picture, illustration, etc.
Object name is 10.1177_2325967120922764-fig2.jpg

DEVELOPMENT (PRIVATE) QUESTIONS

APPROXIMATE DATE OF INJURY:___/____/___

Diagnosis (if unknown, please describe your injury): _______________________

□ New injury □ Same pain/similar symptoms

□ 1 Head/neck □ 2 Shoulder □ 3 Elbow □ 4 Hand/wrist □ 5 Hip/pelvis/thigh

□ 6 Low back □ 7 Knee □ 8 Leg □ 9 Foot/ankle □ 10 Other______________________

□ 5 – participation remained normal

□ 4 – participation remained normal, but pain occurred follow activity/sport

□ 3 – pain during activity that affected performance, but continued activity

□ 2 – pain during activity caused you to stop activity/sport

□ 1 – pain prevented any participation in sports activity

□ 0 □ 1□ 2 □ 3 □ 4 □ 5 □ 6 □ 7 □ 8 □ 9 □ 10 □ 11 □ 12 □ 13 □ 14 □ 15 □ 16 □ 17 □ 18 □ 19 □ 20

(if more than 20, please write the number of days) ______

□ Yes □ No If Yes, approximately how much did you grow in the 6 months prior to injury? _____inches

(If your answer to #10 is “no ”, then you are done . If, “ yes ,” please continue )

Multivariable ORs for Injury Status Using Expanded Definition of Sport Specialization a

Multivariable ORs for Injury Status Using Data Collected From First 2 Years a

Multivariable ORs for Injury Status Using Data Collected From First Year a

Final revision submitted January 20, 2020; accepted February 12, 2020.

One or more of the authors has declared the following potential conflict of interest or source of funding: Research funding for this study was provided by consecutive grants from the American Medical Society for Sports Medicine (AMSSM). AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

Ethical approval for this study was obtained from Ann & Robert H. Lurie Children’s Hospital of Chicago (No. 2011-14567) and the Stritch School of Medicine, Loyola University Chicago.

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Article contents

Psychological responses to sport injury.

  • Britton W. Brewer Britton W. Brewer Springfield College
  • https://doi.org/10.1093/acrefore/9780190236557.013.172
  • Published online: 24 May 2017

In addition to the disruptive impact of sport injury on physical functioning, injury can have psychological effects on athletes. Consistent with contemporary models of psychological response to sport injury, aspects of psychological functioning that can be affected by sport injury include pain, cognition, emotion, and behavior. Part of the fabric of sport and ubiquitous even among “healthy” athletes, pain is a common consequence of sport injury. Postinjury pain is typically of the acute variety and can be exacerbated, at least temporarily, by surgery and some rehabilitation activities. Cognitive responses to sport injury include appraising the implications of the injury for one’s well-being and ability to manage the injury, making attributions for injury occurrence, using cognitive coping strategies, perceiving benefits of injury, and experiencing intrusive injury-related thoughts and images, increased perception of injury risk, reduced self-esteem and self-confidence, and diminished neurocognitive performance. Emotional responses to sport injury tend to progress from a preponderance of negative emotions (e.g., anger, confusion, depression, disappointment, fear, frustration) shortly after injury occurrence to a more positive emotional profile over the course of rehabilitation. A wide variety of personal and situational factors have been found to predict postinjury emotions. In terms of postinjury behavior, athletes have reported initiating coping strategies such as living their lives as normally as possible, distracting themselves, seeking social support, isolating themselves from others, learning about their injuries, adhering to the rehabilitation program, pursuing interests outside sport, consuming alcohol, taking recreational and/or performance-enhancing substances, and, in rare cases, attempting suicide. Psychological readiness to return to sport after injury is an emerging concept that cuts across cognitive, emotional, and behavioral responses to sport injury.

  • sport injury
  • rehabilitation
  • consequences
  • psychological

Introduction

Inherent in sport participation is the risk of injury. Although the physical effects of sport injury (e.g., tissue damage, initiation of healing processes, increased body mass index and body fat percentage) are especially salient (Myer et al., 2014 ; Prentice, 2011 ), sport injury can also have psychological consequences. Aspects of psychological functioning that can be affected by sport injury include pain, cognition, emotion, behavior, and readiness to return to sport. These aspects can be considered in terms of theoretical, empirical, and practical perspectives.

Theoretical Perspectives

To describe and explain how athletes respond psychologically to injury, researchers have borrowed and, in some cases, adapted theories and models from other areas of psychology. For example, the most comprehensive attempt to represent psychological responses to sport injury and their antecedents conceptually—the integrated model of psychological response to sport injury (Wiese-Bjornstal, Smith, Shaffer, & Morrey, 1998 )—is based largely on principles from the literature on stress and coping (Lazarus & Folkman, 1984 ) and is an extension of several previously adapted models (e.g., Gordon, 1986 ; Weiss & Troxel, 1986 ). In the integrated model, sport injury is conceptualized as a stressor that athletes interpret (or “appraise”) in terms of its impact and their ability to deal with its effects. This cognitive appraisal process is thought to be influenced by a multitude of personal and situational factors. Personal factors include injury characteristics (e.g., severity, type) and individual difference variables in the psychological (e.g., personality, motivation, identity), demographic (e.g., age, gender), and physical (e.g., health status, eating behavior) domains. Situational factors pertain to aspects of the sport (e.g., level of competition, time of the competitive season), social (e.g., family dynamics, social support), and physical (accessibility to rehabilitation, comfort of rehabilitation sessions) environments. The resulting cognitive appraisals are posited to influence cognitive, emotional, and behavioral responses to sport injury, which are themselves proposed to be dynamic, reciprocally related, and potentially influential on injury recovery outcomes (Wiese-Bjornstal et al., 1998 ). Research has provided consistent support for predictions generated from the integrated model (for a review, see Brewer, 2007 ). Although the integrated model does not include pain and psychological readiness to return to sport, it could easily be expanded to do so.

Another group of models has adapted the widely known ideas of Kübler-Ross ( 1969 ) regarding adjustment to terminal illness to psychological responses to sport injury. Such grief-based “stage models” hold that athletes proceed through an invariant, predictable sequence of stages after injury. For example, several authors (Astle, 1986 ; Rotella, 1985 ) proposed that athletes display denial, anger, bargaining, depression, and, finally, acceptance after they become injured. Although athletes have exhibited grief-like reactions to serious injury (Macchi & Crossman, 1996 ) and tended to display more favorable psychological responses over time after injury (e.g., McDonald & Hardy, 1990 ; Smith, Scott, O’Fallon, & Young, 1990 ), the notion of an invariant series of psychological reactions to sport injury has not been supported by research (Brewer, 1994 ). As with the integrated model, stage models do not address pain and psychological readiness to return to sport.

Focused on the types of pain that athletes might encounter both before and after injury, Addison, Kremer, and Bell ( 1998 ) developed a model of sport-related pain that incorporates ideas from the gate control theory of pain (Melzack & Wall, 1965 ), the parallel processing model of pain (Leventhal & Everhart, 1979 ), and the literature on cognitive appraisal processes in stress and coping (Lazarus & Folkman, 1984 ). As specified in the model, which neatly dovetails with the integrated model of Wiese-Bjornstal et al. ( 1998 ), athletes experience postinjury pain when they interpret physiological sensations as indicating a threat to their health and ascribe the sensations to injury. Individual differences in age, attention to bodily symptoms, fitness, and physiology are thought to influence the detection of physiological sensations. Both intrinsic factors (e.g., affect, cognition, pain tolerance, personality) and extrinsic factors (e.g., culture, prior experience, social/situational context) are proposed to affect the appraisal process. The model holds that when athletes with injury appraise physiological sensations as pain due to their injury, their responses (e.g., reducing physical activity, seeking assistance, implementing a coping strategy) are subject to the influence of factors such as culture and motivation. Although the model is of potential utility in understanding pain after the occurrence of sport injury, research support for the model is scant.

One particular behavioral response to sport injury—adherence to sport injury rehabilitation—has been examined from a variety of theoretical perspectives. Because adherence to medical regimens has been a widely studied topic for many decades (Meichenbaum & Turk, 1987 ), investigators of adherence to sport injury rehabilitation have had numerous theories and models of adherence available to guide their research. Among the perspectives that have been applied in studies of sport injury rehabilitation are, in addition to the integrated model of psychological response to sport injury (Wiese-Bjornstal et al., 1998 ), personal investment theory (Maehr & Braskamp, 1986 ), protection motivation theory (Prentice-Dunn & Rogers, 1986 ), self-determination theory (Ryan & Deci, 2000 ), the transtheoretical model (Prochaska & DiClemente, 1983 ), and an adaptation of the theory of planned behavior (Levy, Polman, & Clough, 2008 ). In general, the perspectives have strong cognitive and motivational components, which is not surprising given the effort and persistence that adherence to sport injury rehabilitation programs can require.

Although psychological readiness to return to sport is a concept that is still being defined, it has not been completely atheoretical. In particular, it has been suggested that self-determination theory (SDT; Ryan & Deci, 2000 ) offers a viable explanation for why athletes might or might not be psychologically ready to return to sport after injury. Podlog and his colleagues (e.g., Podlog & Eklund, 2005 , 2007 ; Podlog, Lochbaum, & Stevens, 2010 ) have provided empirical support for the contention that, consistent with SDT, athletes can be considered less psychologically ready to return to sport when their basic psychological needs for competence, relatedness, and autonomy are not being satisfied than when those needs are being met.

Empirical Perspectives

Although the first empirical study on psychological responses to sport injury was conducted by Little ( 1969 ) more than a half-century ago, it wasn’t until the 1990s that a steady stream of empirical investigations began to appear in the literature. Over the past quarter-century, a sizable body of research on the topic has accumulated. The primary foci of scientific studies have varied over time, but pain, cognition, emotion, behavior, and readiness to return to sport have all been examined by investigators.

Pain is ubiquitous in sport. It not only can signal the occurrence of sport injury and feature in its aftermath, but it also can be a central aspect of sport training and competition. Reflecting the prominent role of pain in sport, scholars have investigated multiple aspects of the phenomenon in the context of sport. Research has progressed along four main lines of inquiry. One line of research has examined pain from a sociological perspective, yielding the important finding that sport is a culture in which athletes can be reinforced (or even glorified) for ignoring, denying, and playing through pain and injury (e.g., Hughes & Coakley, 1991 ; Nixon, 1992 ). Pain, therefore, appears to be a socially charged psychological response to sport injury that athletes may be discouraged from expressing, even to those responsible for treating the conditions that precipitated it (Safai, 2003 ; Walk, 1997 ).

A second line of research has compared athletes and nonathletes on laboratory measures of pain tolerance and pain threshold. Results of a meta-analysis of 15 studies indicated that (1) athletes had higher pain tolerance than nonathletes for cold, electrical, heat, ischemic, and pressure stimul; and (2) athletes had higher pain threshold than nonathletes for cold and pressure stimuli (Tesarz, Schuster, Hartmann, Gerhardt, & Eidt, 2012 ). The relevance of these findings for pain in response to sport injury, however, is not clear.

A third line of research has focused on assessing the prevalence and identifying anthropometric, biomechanical, strength, training, and, in rare cases, psychological predictors of pain in athletes. Many of the studies in this area of inquiry have examined pain in particular parts or regions of the body experienced by athletes participating in sports in which such pain is likely. For example, investigators have studied shoulder pain in swimmers (Walker, Gabbe, Wajswelner, Blanch, & Bennell, 2012 ); leg pain in cross country runners (Reinking, Austin, & Hayes, 2010 ); wrist pain in gymnasts (DiFiori, Puffer, Aish, & Dorey, 2002 ); knee pain in athletes across a variety of sports (Hahn & Foldspang, 1998 ); patellofemoral pain in basketball, soccer, and volleyball players (Myer et al., 2015 ); low back pain in cross country skiers, orienteers, and rowers (Foss, Holme, & Bahr, 2012 ); and pain in various body locations in cyclists (Dahlquist, Leisz, & Finkelstein, 2015 ). Although the methods and criteria used to examine pain have varied considerably across studies, prevalence rates in excess of 80% for at least mild pain have been documented (e.g., DiFiori et al., 2002 ; Reinking et al., 2010 ). Overall, the findings in this area of research attest to the ubiquity of pain in sport, but they do not have clear implications for understanding pain as a psychological response to injury because many of the participants who reported experiencing pain were not necessarily injured per se and, even when injured, may have been training as much as those who were not injured (Dahlquist et al., 2015 ).

The fourth main line of research has explored pain experienced by athletes after anterior cruciate ligament (ACL) reconstruction. In addition to examining associations of factors such as surgical procedures (Beck et al., 2004 ; Benea et al., 2014 ; Niki et al., 2012 ), anesthesia (Ekmekci et al., 2013 ), clinical variables (Niki et al., 2012 ), and cryotherapy (Raynor, Pietrobon, Guller, & Higgins, 2005 ) with postoperative pain, researchers have obtained descriptive data on the quality of pain over the first 48 hours postsurgery (Tripp, Stanish, Coady, & Reardon, 2004 ) and the intensity of pain over the first 6 weeks postsurgery (Brewer et al., 2007 ; Oztekin, Boya, Ozcan, Zeren, & Pinar, 2008 Tripp et al., 2004 ; Tripp, Stanish, Reardon, Coady, & Sullivan, 2003 ). Athletes’ endorsement of adjectives to describe their pain (e.g., sharp, tender, throbbing, aching, tiring, pulling) seems to change slightly from 24 to 48 hours postsurgery (Tripp et al., 2004 ), and pain intensity tends to decrease steadily from 24 hours to 6 weeks postsurgery (Brewer et al., 2007 ; Oztekin et al., 2008 ; Tripp et al., 2004 ). Pain intensity is higher for adolescents than adults at 24 hours postsurgery (Tripp et al., 2003 ) but is higher for older individuals than younger individuals over the first 6 weeks postsurgery (Brewer et al., 2007 ). Pain intensity is positively associated with anxiety at 24 hours postsurgery (Tripp et al., 2004 ) and negative mood over the first 6 weeks postsurgery (Brewer et al., 2007 ). In general, research in this line of inquiry is more concentrated on pain as a psychological response than that in the other three lines, but the narrow focus on a single type of injury and approach to treatment limits its generalizability. Thus, although the four lines of research have been informative, limitations with each of them preclude a thorough understanding of pain responses to sport injury.

As noted in the general section on theoretical perspectives, the integrated model of psychological response to sport injury (Wiese-Bjornstal et al., 1998 ) and earlier models emanating from the Lazarus and Folkman ( 1984 ) approach to stress and coping (e.g., Gordon, 1986 ; Weiss & Troxel, 1986 ) ascribe a temporally primary role to cognitive appraisals of the impact or personal relevance of sport injury in determining the cognitive, emotional, and behavioral responses that follow. In light of the physical damage induced by injury and the ramifications of that damage for subsequent sport participation, it is not surprising that interpretations of sport injury as threatening or involving harm or loss are common (Clement & Arvinen-Barrow, 2013 ; Ford & Gordon, 1999 ; Gould, Udry, Bridges, & Beck, 1997a ). Cognitive responses beyond the primary appraisals of the injury can be grouped into three potentially overlapping categories of cognitive content (i.e., injury-related, self-related, and coping-related) and one general category of cognitive processes.

Injury-related content

Given that sport injury is the kind of event that elicits the psychological responses addressed in this article, it is logical to expect the cognitive content of athletes with injuries to reflect their experiences and pertain at least partially to the injuries themselves. The unexpected nature of sport injuries may prompt athletes to engage in attributional thinking (Wong & Weiner, 1981 ) in which they attempt to identify the cause (or causes) of their injuries. A trio of studies identified behavioral factors (San José, 2003 ; Tedder & Biddle, 1998 ) and mechanical/technical factors (Brewer, 1999a ) as common explanations given by athletes for injury occurrence. In addition to cognitions about the causes(s) of their injuries, athletes have reported experiencing recurrent, distress-producing, recurrent, intrusive thoughts and images of the injury event (Newcomer & Perna, 2003 ; Shuer & Dietrich, 1997 ; Vergeer, 2006 ). Later, after the immediate impact of injury has passed, athletes have shown a propensity for experiencing more positively tinged cognitive content, reporting perceptions of benefits they have accrued as a result of their injuries (e.g., Ford & Gordon, 1999 ; Podlog & Eklund, 2006 ; Tracey, 2003 ; Udry, Gould, Bridges, & Beck, 1997 ; Wadey, Evans, Evans, & Mitchell, 2011 ). Common themes of the injury-related benefits identified by athletes include personal growth, psychologically based performance enhancement, and physical/technical development (Udry et al., 1997 ). After experiencing injury, athletes may also harbor negative cognitive content about their prospects with respect to future injury, reporting less confidence in their ability to avoid injury and higher levels of perceived risk of injury and worry about sustaining an injury than athletes without a recent injury (Reuter & Short, 2005 ; Short, Reuter, Brandt, Short, & Kontos, 2004 ).

Self-related content

For many athletes, injury threatens their involvement in a self-defining activity that serves as a significant source of self-worth (Brewer, Van Raalte, & Linder, 1993 ). Consequently, it is reasonable to expect that injury might have an impact on self-related cognitive content. Consistent with this notion, athletes have reported decreases in self-esteem after injury (Leddy, Lambert, & Ogles, 1994 ), increases in self-confidence and self-efficacy over the course of rehabilitation (Quinn & Fallon, 1999 ; Thomeé et al., 2007 ), and decreases in self-identification with the athlete role (Brewer, Cornelius, Stephan, & Van Raalte, 2010 ). Substantial changes in self-definition, which reflects how athletes think about themselves, have been reported by athletes with severe injuries (Vergeer, 2006 ).

Coping-related content

In taking an active role to deal with the adverse physical and psychological effects of injury, athletes have reported that they sometimes initiate cognitive coping strategies. Among the common themes of the cognitive content used by athletes to cope with injury are acceptance of injury, disengagement from injury, imagery, positive thoughts, and recovery (Bianco, Malo, & Orlick, 1999 ; Carson & Polman, 2008 , 2010 ; Gould, Udry, Bridges, & Beck, 1997b ; Ruddock-Hudson, O’Halloran, & Murphy, 2014 ; Tracey, 2003 ; Udry et al., 1997 ). It appears that the cognitive strategies deployed by athletes are at least in part influenced by the specific qualities of the injury-related stressors (e.g., physical symptoms, rehabilitation requirements) with which they are dealing, as the use of various coping strategies fluctuates over the course of rehabilitation (Johnston & Carroll, 2000 ; Udry, 1997 ) and differs as a function of whether athletes have chronic or acute injuries (Wasley & Lox, 1998 ).

The literature suggests that, in addition to affecting cognitive content, sport injury has an adverse effect on cognitive processes such as attention, memory, processing speed, and reaction time (Moser, 2007 ). Postinjury impairment of cognitive functioning has also been found for musculoskeletal injuries in one study (Hutchison, Comper, Mainwaring, & Richards, 2011 ), but not in another (Mrazik, Brooks, Jubinville, Meeuwisse, & Emery, 2016 ). Presumably, the intrusive images of injury occurrence (Shuer & Dietrich, 1997 ; Vergeer, 2006 ) noted in the section on injury-related content occupy some of the cognitive resources that would otherwise be devoted to processing other information and, along with postinjury emotional disturbance, may partially explain how musculoskeletal injuries might produce impaired cognitive functioning.

The largest share of research on the psychological consequences of sport injury has been devoted to emotional responses. Findings from an abundance of qualitative and quantitative studies have converged to produce a rich description of how athletes respond emotionally to injury and identify a variety of personal, situational, cognitive, and behavioral factors associated with those responses.

From a descriptive standpoint, athletes have tended to use a variety of negative terms (e.g., anger, bitterness, confusion, depression, fear, frustration, helplessness, shock) to characterize their emotions after injury (e.g., Bianco et al., 1999 ; Wadey, Evans, Hanton, & Neil, 2012a ). Although common, reports of negative emotions are not inevitable and may fluctuate widely over the course of the rehabilitation (Bianco et al., 1999 ; Carson & Polman, 2008 ; Johnston & Carroll, 1998 ). In general, however, there is evidence that athletes tend to report higher levels of emotional disturbance after sustaining an injury than they do before being injured (Appaneal, Levine, Perna, & Roh, 2009 ; Leddy, Lambert, & Ogles, 1994 ; Mainwaring et al., 2004 ; Mainwaring, Hutchinson, Biscchop, Comper, & Richards, 2010 ; Olmedilla, Ortega, & Goméz, 2014 ; Smith et al., 1993 ) and that athletes with injury tend to report higher levels of emotional disturbance than athletes without injury (Abenza, Olmedilla, & Ortega, 2010 ; Appaneal et al., 2009 ; Brewer & Petrie, 1995 ; Johnson, 1997 , 1998 ; Leddy et al., 1994 ; Mainwaring et al., 2004 ; Pearson & Jones, 1992 ; Smith et al., 1993 ). Estimates of the prevalence of athletes with injury who report clinically meaningful levels of emotional disturbance have ranged from 5 to 42% (Appaneal et al., 2009 ; Brewer, Linder, & Phelps, 1995 ; Brewer, Petitpas, Van Raalte, Sklar, & Ditmar, 1995 ; Brewer & Petrie, 1995 ; Garcia et al., 2015 ; Leddy et al., 1994 ; Manuel et al., 2002 ). Most of the psychological distress reported by athletes would be classified as “subclinical,” lacking the severity and/or duration to be considered a clinical condition.

In addition to the large body of research that has provided a thorough description of emotional responses to sport injury, numerous studies have investigated potential predictors of such responses. As proposed in the integrated model of psychological response to sport injury (Wiese-Bjornstal et al., 1998 ), associations have been documented between postinjury emotional responses and a wide variety of personal and situational factors (which presumably affect emotional responses through cognitive appraisals), cognitive responses, and behavioral responses (the latter of which will be discussed in the section on behavior that follows). Regarding personal factors, positive associations have been obtained between postinjury emotional disturbance and pain (Brewer et al., 2007 ), pain catastrophizing (Baranoff, Hanrahan, & Connor, 2015 ), neuroticism (Brewer et al., 2007 ), impairment in performing daily activities (Crossman & Jamieson, 1985 ), injury acuteness (Alzate, Ramírez, & Artaza, 2004 ; Brewer, Linder, & Phelps, 1995 ), injury severity (Alzate et al., 2004 ; Manuel et al., 2002 ; Smith, Scott, O’Fallon, & Young, 1990 ), self-identification with the athlete role (Baranoff et al., 2015 ; Brewer, 1993 ; Manuel et al., 2002 ), and investment in playing sports professionally (Kleiber & Brock, 1992 ). Negative association has been documented between postinjury emotional disturbance and age (Brewer, Linder, & Phelps, 1995 ; Smith, Scott, O’Fallon, & Young, 1990 ), hardiness (Wadey, Evans, Hanton, & Neil, 2012b ), injury recovery (McDonald & Hardy, 1990 ; Smith, Young, & Scott, 1988 ), and acceptance of uncomfortable experiences (Baranoff et al., 2015 ).

With respect to situational factors, the variable most consistently associated with postinjury emotional responses is the amount of time that has passed since occurrence of the injury. With the exception of a possible increase in the intensity of negative emotions and a decrease in the intensity of positive emotions at the end of rehabilitation with a return to sport looming (Morrey, Stuart, Smith, & Wiese-Bjornstal, 1999 ), negative emotions tend to decrease in intensity, and positive emotions tend to increase in intensity as time passes after injury (Appaneal et al., 2009 ; Brewer et al., 2007 ; Garcia et al., 2015 ; Leddy et al., 1994 ; Macchi & Crossman, 1996 ; Mainwaring et al., 2004 , 2010 ; Manuel et al., 2002 ; McDonald & Hardy, 1990 ; Olmedilla et al., 2014 ; Quinn & Fallon, 1999 ; Smith, Scott, O’Fallon, & Young, 1990 ). Other situational factors for which associations with high levels of emotional disturbance have been documented in multiple studies include high levels of life stress (Albinson & Petrie, 2003 ; Brewer, 1993 ; Brewer et al., 2007 ; Manuel et al., 2002 ) and low levels of both social support for rehabilitation (Brewer, Linder, & Phelps, 1995 ; Rees, Mitchell, Evans, & Hardy, 2010 ) and satisfaction with social support (Green & Weinberg, 2001 ; Manuel et al., 2002 ).

Cognitive responses related to greater postinjury emotional disturbance in athletes include perceptions of being unable to cope with injury (Albinson & Petrie, 2003 ; Daly, Brewer, Van Raalte, Petitpas, & Sklar, 1995 ), high levels of avoidance-focused (Gallagher & Gardner, 2007 ) and low levels of instrumental coping strategies (Wadey, Clark, Podlog, & McCullough, 2013 ), and causal attributions for sport injury occurrence (Brewer, 1999a ; Tedder & Biddle, 1998 ). Emotional disturbance was positively associated with attributing the cause of injury to internal factors in one study (Tedder & Biddle, 1998 ) but negatively associated with attributing the cause of injury to internal and stable factors in a second study (Brewer, 1999a ). Behaviors associated with athletes’ emotional responses to injury are identified next.

Because pain, cognition, and emotion can be readily concealed from view, behavior is undeniably the most overt psychological response to sport injury. Further, even though the behavior of athletes may reflect or be a manifestation of their experience of pain, cognitive, or emotional responses to injury, it is behavioral responses that have the greatest potential to affect the rehabilitation process. Some of the behaviors that athletes have reported themselves as engaging in after injury can be interpreted as attempts to cope with the challenges of the situation. For example, such active, instrumental, “problem-focused” coping behaviors as pursuing rehabilitation vigorously, learning about the injury, trying alternative treatments, building physical strength, and cultivating or enlisting social resources (Bianco et al., 1999 ; Gould et al., 1997b ; Johnston & Carroll, 2000 ; Quinn & Fallon, 1999 ; Ruddock-Hudson et al., 2014 ; Wadey et al., 2012a , 2012b ) tend to be deployed under conditions of elevated stress and mood disturbance (Albinson & Petrie, 2003 ) and conceivably can be of utility in helping athletes to recover from their injury and return to sport. Even some avoidant or “emotion-focused” coping behaviors such as distracting oneself (e.g., keeping busy, watching television) and isolating oneself from others (Bianco et al., 1999 ; Carson & Polman, 2010 ; Gould et al., 1997b ; Ruddock-Hudson et al., 2014 ; Wadey et al., 2012a , 2012b ) may be useful in the regulation of postinjury emotions (Carson & Polman, 2010 ). Other behavioral responses to sport injury, however, such as attempting suicide (Smith & Milliner, 1994 ), engaging in disordered eating (Sundgot-Borgen, 1994 ), consuming banned substances (National Collegiate Athletic Association, 2012 ), and drinking alcohol (Martens, Dams-O’Connor, & Beck, 2006 ) may have less adaptive consequences.

The behavioral response to sport injury that has garnered the most attention from investigators is adherence to rehabilitation. Considered vital to the success of sport injury rehabilitation programs (Fisher, Domm, & Wuest, 1988 ), adherence in this context refers to the extent to which athletes follow the prescribed course of treatment. The specific behaviors involved in adhering to rehabilitation vary substantially across the range of injuries that athletes incur, but some of the more common behavioral requirements of sport injury rehabilitation programs include “attending and actively participating in clinic-based rehabilitation appointments, avoiding potentially harmful activities, wearing therapeutic devices (e.g., orthotics), consuming medications appropriately, and completing home rehabilitation activities (e.g., exercises, therapeutic modalities)” (Brewer, 2004 , pp. 39–40). Although athletes engage in some of the rehabilitation behaviors in supervised clinical settings, they complete other of the behaviors at home, away from the direct oversight of rehabilitation professionals. The considerable variation in average adherence levels reported in research investigations (ranging from 40 to 91%, as reported in a review of the literature [Brewer, 1999b ]) is not surprising in light of the vast array of injuries, rehabilitation programs, clinical settings, and methods of assessment (e.g., self-report, practitioner rating, attendance log) that have been examined. Further complicating the estimation of adherence in the context of sport injury rehabilitation is that some highly motivated athletes may “overadhere” to their rehabilitation program by engaging in rehabilitation activities to a greater extent than recommended by the sports health care professional treating them (Niven, 2007 ; Podlog, Gao et al., 2013 ). Although such behavior is technically nonadherent, it is fundamentally different from failing to complete one or more aspects of a rehabilitation program.

Given the potential importance of adherence in achieving desired sport injury rehabilitation outcomes, investigators have attempted to identify factors associated with adherence to sport injury rehabilitation. As in the general medical literature, in which literally hundreds of predictors of treatment adherence have been identified (Meichenbaum & Turk, 1987 ), research has documented numerous correlates of sport injury rehabilitation adherence that can be grouped into the main conceptual categories of the integrated model of psychological response to sport injury (Wiese-Bjornstal et al., 1998 ). Examples of personal factors for which positive associations with sport injury rehabilitation adherence have been found in multiple studies include (perceived) injury severity (Grindley, Zizzi, & Nasypany, 2008 ; Taylor & May, 1996 ), athletic identity (Brewer, Cornelius, Van Raalte, Petitpas, Sklar et al., 2003b ; Brewer, Cornelius, Van Raalte, Tennen, & Armeli, 2013 ), pain tolerance (Byerly, Worrell, Gahimer, & Domholdt, 1994 ; Fields, Murphey, Horodyski, & Stopka, 1995 ; Fisher et al., 1988 ), and self-motivation (Brewer, Van Raalte, Cornelius et al., 2000 ; Duda, Smart, & Tappe, 1989 ; Fields et al., 1995 ; Fisher et al., 1988 ; Levy et al., 2008 ). With respect to situational factors, findings from multiple investigations have shown that athletes display higher levels of adherence to sport injury rehabilitation programs when they consider themselves as receiving support from others for their rehabilitation (Byerly et al., 1994 ; Duda et al., 1989 ; Fisher et al., 1988 ; Johnston & Carroll, 2000 ; Levy et al., 2008 ), perceive the clinic setting in which they do their rehabilitation as comfortable, and view their clinic-based rehabilitation appointments as conveniently scheduled (Fields et al., 1995 ; Fisher et al., 1988 ).

Several cognitive and emotional responses have also been found to predict adherence to sport injury rehabilitation programs across multiple studies. From a cognitive standpoint, athletes have demonstrated higher levels of adherence to rehabilitation when they report believing that their treatment will be effective (Brewer, Cornelius, Van Raalte, Petitpas, Sklar et al., 2003a ; Duda et al., 1989 ; Taylor & May, 1996 ), profess a strong intention to adhere to rehabilitation (Bassett & Prapavessis, 2011 ; Levy et al., 2008 ), and indicate that they are confident that they can cope with their injuries (Daly et al., 1995 ; Levy et al., 2008 ) and complete their rehabilitation program (Brewer, Cornelius, Van Raalte, Petitpas, Sklar et al., 2003a ; Levy et al., 2008 ; Taylor & May, 1996 ; Wesch et al., 2012 ). In terms of emotional responses, negative associations have been documented between mood disturbance and sport injury rehabilitation adherence (Alzate et al., 2004 ; Daly et al., 1995 ).

Psychological Readiness to Return to Sport

The lack of a universally accepted definition of psychological readiness to return to sport after injury has not prevented researchers from investigating the topic through two main approaches. One approach involves comparing athletes who return to sport after injury with those who do not return to sport after injury on psychological variables measured during or after rehabilitation. The other approach involves asking athletes who have returned to sport after injury to describe their experience of returning. Reviews of research in which the two approaches have been implemented have yielded a consistent set of psychological factors associated with athletes’ return to sport after injury (Ardern, Taylor, Feller, & Webster, 2013 ; Czuppon, Racette, Klein, & Harris-Hayes, 2014 ; Podlog & Eklund, 2007 ). Specifically, the empirical findings of prospective and retrospective studies have dovetailed, suggesting that factors involved in psychological readiness to return to sport after injury include a lack of fear or anxiety regarding reinjury, confidence in the injured body part and in one’s ability to perform, and intrinsic motivation to return to sport.

The consequences of an absence of psychological readiness to return to sport are not fully understood. Beyond being less likely to return to sport in the first place, athletes who are not psychologically ready to return to sport but do so anyway may be at increased risk for such consequences as injury (or reinjury), poor sport performance, and a lower quality sport experience. Prospective longitudinal research is needed to investigate these possibilities.

Practical Perspectives

From an applied standpoint, numerous interventions have been implemented to affect athletes’ psychological responses to sport injury. Common treatment approaches for pain differ somewhat from those for problematic cognitive, emotional, and behavioral responses, and treatments designed to enhance psychological readiness to return to sport have not been evaluated explicitly. Consequently, interventions to treat pain and improve psychological readiness to return to sport are discussed separately from the other three main types of psychological response and from each other.

An important aspect of postinjury pain among athletes is that it often can be escaped or reduced by ceasing, reducing, or modifying involvement in activities that produce or exacerbate the pain. For postinjury pain that is especially intense or long-lasting, formal pain management interventions can be initiated. Such interventions are likely to involve a combination of analgesic medications and physical therapies (Kolt, 2004 ). Aspirin, ibuprofen, and paracetamol (acetaminophen) are the analgesic medications most likely to be recommended, with opioids (e.g., codeine) and corticosteroids prescribed less frequently (Garnham, 2007 ). Physical therapies used to treat postinjury pain in athletes include electrophysical agents (e.g., transcutaneous electrical nerve stimulation [TENS], interferential electrical stimulation, ultrasound), manual techniques (e.g., massage, chiropractic manipulation), exercise, cryotherapy, heat, and acupuncture (Kolt, 2007 ; Snyder-Mackler, Schmitt, Rudolph, & Farquhar, 2007 ; Wadsworth, 2006 ). Although a wide variety of psychological techniques have been recommended to help athletes cope with postinjury pain (Kolt, 2004 , 2007 ), the effectiveness of such techniques in the context of sport injury has been evaluated in very few controlled experimental studies (Cupal & Brewer, 2001 ; Ross & Berger, 1996 ). The lack of research on psychological pain management techniques in sport injury rehabilitation suggests that the techniques are not implemented on a widespread basis in clinical settings.

Cognitive, Emotional, and Behavioral Responses

As for postinjury pain, many psychological interventions have been advocated to affect cognitive, emotional, and behavioral responses to sport injury. Only a few of the interventions, however, have received experimental support for influencing cognitive, emotional, and/or behavioral responses in sport injury rehabilitation. Interventions found effective relative to a control condition include goal setting (Evans & Hardy, 2002 ; Penpraze & Mutrie, 1999 ), imagery (Cupal & Brewer, 2001 ), modeling (Maddison, Prapavessis, & Clatworthy, 2006 ), and multimodal interventions (Johnson, 2000 ; Ross & Berger, 1996 ). These interventions (Christakou, Zervas, & Lavallee, 2007 ; Cupal & Brewer, 2001 ; Maddison et al., 2006 , 2012 ; Newsom, Knight, & Balnave, 2003 ; Ross & Berger, 1996 ; Theodorakis, Beneca, Malliou, & Goudas, 1997 ; Theodorakis, Malliou, Papaioannou, Beneca, & Filactakidou, 1996 ) and others, including biofeedback (Silkman & McKeon, 2010 ) and self-talk (Beneka et al., 2013 ), have been found to influence physical outcomes in sport injury rehabilitation.

As an emerging construct, psychological readiness to return to sport after injury has received minimal attention from researchers attempting to evaluate the effectiveness of interventions designed explicitly to foster psychological readiness in athletes resuming sport participation after injury. Nevertheless, interventions that have produced increases in confidence (e.g., Maddison et al., 2006 ) and decreases in anxiety (e.g., Cupal & Brewer, 2001 ; Ross & Berger, 1996 ), for example, may have enhanced the readiness of the athletes receiving the interventions to return to sport with or without the intention of actually doing so. As a fuller understanding of the composition of what it means to be psychologically ready to return to sport emerges, inquiry into the effects of interventions developed to enhance readiness is likely to ensue.

Conclusions

Sport injury can affect athletes both physically and psychologically. Pain, cognition, emotion, and behavior are primary areas of psychological functioning affected by injury. Psychological responses to sport injury tend to be strongest in close temporal proximity to injury occurrence and fluctuate over the course of rehabilitation. Psychological readiness to return to sport after injury is an emerging concept that incorporates aspects of cognition, emotion, and behavior, including anxiety, confidence, motivation, and postreturn expectations. A variety of theoretical perspectives have been used to guide a body of research on psychological responses to sport injury. Relatively few controlled investigations of interventions designed to influence psychological responses to sport injury have been conducted.

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    Sports Medicine. 2012. TLDR. The purpose of this commentary is to outline the rationale for the inclusion and application of behavioural science in reducing the burden of injury by increasing adherence to proven prevention strategies and detail several strategies based on two prominent behavioural theories to aid the reader in conceptualizing ...

  9. Sports Injury Research

    Sports Injury Research Evert Verhagen (ed.), Willem van Mechelen (ed.) Published: 3 December 2009 Cite Permissions Share Abstract With the increasing focus on tackling obesity and other lifestyle-related illnesses and conditions, participation in sports and physical activity is growing.

  10. (PDF) Sport injuries: A review of outcomes

    Ankle ligament injuries in athletes result in incomplete recovery (up to 40% at 6 months), and OA in the long term (latency period more than 25 years). Spine pathologies are associated more ...

  11. Full article: Sport injury psychology: An overview and introduction to

    Welcome to this special issue of the Journal of Applied Sport Psychology on Sports Injury Psychology. We introduce this special issue in the knowledge that just over 20 years ago, Britton Brewer was tasked with a similar introduction to write as Guest Editor of the 1998 special issue (Brewer, Citation 1998).At that point in time, Brewer remarked that a special issue was timely given the ...

  12. (PDF) SPORTS INJURY PREVENTION: A CONCISE REVIEW

    Results: Pre-participation screening is used to identify conditions that might adversely affect sport participation and identify injury risk, need for pre-habilitation or rehabilitation, as...

  13. Risk of Injuries Associated With Sport Specialization and Intense

    PMCID: PMC7318830 PMID: 32637428 Risk of Injuries Associated With Sport Specialization and Intense Training Patterns in Young Athletes: A Longitudinal Clinical Case-Control Study Neeru Jayanthi, MD, *†‡ Stephanie Kleithermes, PhD, § Lara Dugas, PhD, ∥ Jacqueline Pasulka, DO, ¶ Sara Iqbal, BS, # and Cynthia LaBella, MD **††

  14. (PDF) Common sports injuries

    This paper will review the general common sports injuries. Sample of ankle sprain injury [8] Sample of elbow strain injury [9] Sample of ankle dislocation injury [10] Types of bone...

  15. Sport psychology education for sport injury rehabilitation

    1. Introduction. Sport psychology intervention has been shown to benefit sport injury rehabilitation (Armatas, Chondrou, Yiannakos, Galazoulas, & Velkopoulos, 2007; Levy, Polman, Clough, & McNaughton, 2006).As such previous research investigating the attitudes and behaviours of sport injury rehabilitation professionals (SIRPs) has indicated that sport psychology education is likely to have a ...

  16. Psychological Responses to Sport Injury

    Introduction. Inherent in sport participation is the risk of injury. Although the physical effects of sport injury (e.g., tissue damage, initiation of healing processes, increased body mass index and body fat percentage) are especially salient (Myer et al., 2014; Prentice, 2011), sport injury can also have psychological consequences.Aspects of psychological functioning that can be affected by ...

  17. Computation

    This research paper examines Sports Analytics, focusing on injury patterns in the National Basketball Association (NBA) and their impact on players' performance. It employs a unique dataset to identify common NBA injuries, determine the most affected anatomical areas, and analyze how these injuries influence players' post-recovery performance. This study's novelty lies in its integrative ...

  18. Sports Injury Research Papers

    Sports Injury Research Papers - Academia.edu Academia.edu no longer supports Internet Explorer. To browse Academia.edu and the wider internet faster and more securely, please take a few seconds to We're Hiring! Help Center View Sports Injury Research Papers on Academia.edu for free.

  19. Sports Injury Research Paper

    Sports Injury Research Paper. Sport injuries are universal and can be commonly found everywhere. These injuries can include a concussion, bone fractures or strains on muscles. Often, these injuries can be minor; however, these injuries contain the chance to be more serious and dangerous. Prevention of the sports injuries is the best way of ...