Context

Sport specialization, commonly defined as intensive year-round training in a single sport to the exclusion of other sports, has been associated with an increased risk for overuse injury. Two pathways to becoming highly specialized are recognized: (1) having only ever played 1 sport (exclusive highly specialized) and (2) quitting other sports to focus on a single sport (evolved highly specialized). Understanding the differences in injury patterns between these groups of highly specialized athletes will inform the development of injury-prevention strategies.

Objective

To compare the distribution of injury types (acute, overuse, serious overuse) among evolved highly specialized athletes, exclusive highly specialized athletes, and low-moderately specialized athletes.

Design

Cross-sectional study.

Setting

Tertiary care pediatric sports medicine clinic between January 2015 and April 2019.

Patients or Other Participants

A total of 1171 patients (age = 12.01–17.83 years, 59.8% female) who played ≥1 organized sports, presented with a sport-related injury, and completed a sports participation survey.

Main Outcome Measure(s)

Distribution of injury types (acute, overuse, serious overuse).

Results

The percentage of injuries due to overuse was similar between the exclusive and evolved highly specialized athletes (59.2% versus 53.9%; P = .28). Compared with low-moderately specialized athletes, exclusive and evolved highly specialized athletes had a higher percentage of overuse injuries (45.3% versus 59.2% and 53.9%, respectively; P = .001). Multivariate analysis of the highly specialized groups revealed sport type to be a significant predictor of a higher percentage of injuries due to overuse, with individual-sport athletes having increased odds of sustaining an overuse injury compared with team-sport athletes (odds ratio = 1.95; 95% CI = 1.17, 3.24).

Conclusions

The distribution of injury types was similar between evolved and exclusive highly specialized youth athletes, with both groups having a higher percentage of injuries due to overuse compared with low-moderately specialized athletes. Among highly specialized athletes, playing an individual sport was associated with a higher proportion of overuse injuries compared with playing a team sport.

Key Points
  • Highly specialized youth athletes who have only ever played 1 sport had an injury distribution similar to that of highly specialized youth athletes who quit other sports to focus on a single sport.

  • Among highly specialized youth athletes, playing an individual sport was associated with a greater proportion of injuries due to overuse versus acute mechanisms when compared with playing a team sport.

An estimated 60 million American children aged 6 to 18 years participate in some form of organized athletics.1  More than 2.5 million sports injuries are estimated to occur in the United States each year among patients 24 years or younger,2  with at least half of the sports injuries seen in emergency rooms being due to overuse.3 Youth sport specialization, which has been defined as “intentional and focused participation in a single sport for a majority of the year that restricts opportunities for engagement in other sports and activities,”4  is thought to be among the driving forces behind the high prevalence of overuse injuries.5  Additionally, emphasis on competitive success, coined the professionalization of youth sports,6  has become widespread. This may lead to more external pressure to begin intense training for a single sport at a young age.7,8  Though many parents and athletes believe that sport specialization will enhance sport performance and career growth, they may underestimate the potential injury risks of sport specialization.911  Along with the increasing prevalence of club sports, in which coaches may be more likely than high school coaches to view sport specialization as a helpful strategy for youth athlete development and sport success,12  such surveys suggest that further research is needed into the potential risks, particularly involving overuse injuries, of early youth sport specialization.

Jayanthi et al13  created a 3-question survey tool that has been used in several other studies1418  to classify an athlete’s level of sport specialization as low, moderate, or high. The questions are (1) “Can you pick a main sport?” (2) “Do you train more than 8 months per year for a main sport?” and (3) “Did you quit other sports to focus on a main sport?” Answering yes to all 3 questions qualifies the respondent as high specialization, yes to 2 questions as moderate specialization, and yes to 0 or 1 question as low specialization.

Miller et al19  found that this specialization scale misclassified 30% of highly specialized athletes as moderately specialized. These are 1-sport athletes who trained >8 months per year but had never played other sports and therefore answered no to the third question, classifying them as moderately specialized. However, based on the consensus definition of sport specialization,4  most experts would classify these athletes as highly specialized. Data are lacking on this subset of highly specialized athletes, which we have labeled exclusive highly specialized. Whether their injury patterns differ from those of highly specialized athletes who have been exposed to other sports (whom we have labeled evolved highly specialized) is unknown.

Sports medicine researchers have theorized that, without exposure to the variety of movement patterns afforded by sport diversification, children who have only ever played 1 sport may develop neuromuscular imbalances that put them at higher risk for injury.20  For example, researchers21,22  have demonstrated improved lower extremity coordination and higher performance in strength and agility tests among multisport athletes compared with single-sport athletes, suggesting that exposure to multiple sports may offer injury protection.

The primary purpose of our study was to determine whether the distribution of injury types (acute versus overuse) among highly specialized athletes differed based on the pathway taken to specialization (evolved versus exclusive). A secondary objective was to separate severe overuse injuries from the remaining overuse injuries and assess if the pathway taken to specialization (exclusive versus evolved) affected the injury distribution (acute, overuse, serious overuse). An additional secondary objective was to compare the distributions of injury types (acute, overuse, serious overuse) between each group of highly specialized athletes and low or moderately specialized athletes. We hypothesized that the exclusive highly specialized athletes would have a higher proportion of overuse injuries than the evolved highly specialized athletes and that both groups of highly specialized athletes would have a higher proportion of overuse injuries compared with the low or moderately specialized athletes.

Design and Study Population

This study received approval from a large academic institutional review board. We conducted a retrospective chart review of patients aged 12 to 17 years who completed a sports participation survey (Appendix) after presenting to a large midwestern sports medicine clinic with a sport-related injury between January 2015 and April 2019. Patients were excluded if they did not play any organized sports, did not fill out the survey completely, or did not have a sport-related injury (Figure 1).

Figure 1

A total of 1647 charts were analyzed; 1171 met the inclusion criteria of participating in an organized sport, fully completing the sports participation survey, and having a sport-related injury.

Figure 1

A total of 1647 charts were analyzed; 1171 met the inclusion criteria of participating in an organized sport, fully completing the sports participation survey, and having a sport-related injury.

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Measurements

Patient information collected from the electronic medical record included patient age, sex, race or ethnicity, date of injury, diagnosis, injury type (acute, overuse, or serious overuse), and the sports participation survey. Injury type was determined from the description of the injury mechanism in the electronic medical record as either acute (from a single, traumatic event) or overuse (gradual onset). Serious overuse injuries were classified based on the Jayanthi et al16  criterion of any overuse injury for which the physician recommended treatment of >1 month of rest from sports. This category contained but was not limited to injuries such as stress fractures, physeal stress injuries, elbow ligament overuse injuries, spondylolysis, and osteochondritis dissecans.

The sports participation survey included questions that classified athletes as low, moderate, or highly specialized according to the 3-point system used by Jayanthi et al,13  whereby 1 point each was assigned for (1) playing only 1 sport, (2) training for that 1 sport >8 months/year, and (3) quitting all other sports to focus on their main sport. However, the survey had an additional question first used by Miller et al19  that asked athletes if they had previously played any other sports.

Based on the responses to those items, we categorized participants into 3 groups: (1) exclusive highly specialized athletes, who played only 1 sport and trained >8 months/year but answered no to the question regarding quitting other sports (because they had never played any other sports); (2) evolved highly specialized athletes, who played only 1 sport, trained >8 months/year for 1 sport, and quit other sports to focus on 1 sport; and (3) low-moderately specialized athletes, who either played multiple sports or trained <8 months/year for a single sport. Low and moderately specialized athletes were combined into a single group, consistent with the methods used by Miller et al19  when developing the exclusive and evolved highly specialized distinctions.

For the highly specialized athletes, sport type was classified as either team or individual according to the same criterion used in previous studies, which defined a team sport as “a sport in which athletes play with others at the time of play.”23,24  The 2 highly specialized athletes who indicated their sport as other were excluded from this part of the analysis.

Statistical Analysis

We performed the statistical analysis using SAS software (version 9.4; SAS Institute Inc). Bivariate analyses, including χ2 tests, t tests, and 1-way analyses of variance, were conducted to compare the demographic characteristics, sport type, injury type, and injury severity among the 3 groups. For the post hoc analysis examining the relationship between sport type and months of rest per year, we calculated 1-way analyses of variance. Two multivariable logistic regression models were fit to predict the likelihood of overuse injury. The first model was predicted by the 3 sport specialization groups (reference: low-moderately specialized), age, and sex. The second logistic regression model was predicted by the 2 highly specialized groups (reference: evolved), age, sex, sport type, starting age of training >8 months per year, and number of months of rest per year. The selection of which predictor variables to include accounted for factors that have been linked to sport specialization and injury risk (age, sex, sport type),13,17  as well as data that were available clinically from the sports participation survey that may affect injury risk (starting age of training >8 months per year, number of months of rest per year). Odds ratios (ORs) and 95% CIs were computed based on the logistic regression models. To adjust for possible collinearity and validate the second regression model, we ran bivariate analyses (χ2 for discrete variables, t test for continuous variables) on each predictor variable individually. A third regression was fit to include only predictor variables determined to have a statistically significant relationship with the overuse injury proportion by the bivariate analyses (sex, age, starting age of training >8 months per year, and sport type). The significance level for all factors was set at P < .05.

Participant Characteristics

Of the 1647 patient charts identified on initial chart review, 1171 (71.1%) patients met the inclusion criteria. Of the 1171 patients, 169 (14.4%) were exclusive highly specialized athletes, 247 (21.1%) were evolved highly specialized athletes, and 755 (64.4%) were low-moderately specialized athletes.

Athlete Demographics

Overall, 700 athletes (59.8%) in our participant population identified as female (Table 1). Girls represented 77.5% of the exclusive highly specialized group, 64.8% of the evolved highly specialized group, and 54.2% of the low-moderately specialized group; the difference in the proportions of female athletes across the 3 groups was significant (P < .0001). The age at presentation to the clinic was similar across specialization groups, with an age of 15.26 years for the exclusive highly specialized group, 15.35 years for the evolved highly specialized group, and 15.23 years for the low-moderately specialized group (P = .57).

Table 1.

Sex Differences Among Specialization Groups, No. (%)

Sex Differences Among Specialization Groups, No. (%)
Sex Differences Among Specialization Groups, No. (%)

The number of months per year of rest from organized sports between the 2 highly specialized groups did not differ, with the exclusive highly specialized group resting for an average of 0.71 months per year and the evolved highly specialized group resting for 0.69 months per year (P = .84). The exclusive highly specialized group began intensive training (>8 months per year) for their main sport at an earlier age than the evolved highly specialized group (8.23 versus 9.62 years, respectively; P < .0001; Table 2).

Table 2.

Demographic Differences Among Specialization Groups

Demographic Differences Among Specialization Groups
Demographic Differences Among Specialization Groups

Sport Type

A higher proportion of the exclusive highly specialized athletes (71.4%) than the evolved highly specialized athletes (55.3%) played a sport classified as individual (P = .0009; Table 3). Gymnastics was the most common individual sport in our study (23.80% overall, 29.0% of the exclusive highly specialized group, and 20.2% of the evolved highly specialized group), and soccer was the most frequent team sport (15.4% overall, 16.6% of the exclusive highly specialized group, and 14.6% of the evolved highly specialized group). Post hoc analysis revealed that individual-sport athletes rested for fewer months per year than team-sport athletes (0.50 versus 1.19, respectively; P < .0001).

Table 3.

Sport Type Differences Between High Specialization Groups, No. (%)

Sport Type Differences Between High Specialization Groups, No. (%)
Sport Type Differences Between High Specialization Groups, No. (%)

Injury Type Distribution

Overuse injuries accounted for 100 of the 169 injuries (59.17%) in the exclusive highly specialized group, 133 of the 247 injuries (53.85%) in the evolved specialized group, and 342 of the 755 injuries (45.30%) in the low-moderately specialized group (Figure 2). In a direct comparison, the proportion of injuries that were overuse did not differ between the exclusive and evolved specialized groups (P = .29). When directly compared with the low-moderate group, the proportions of injuries that were overuse were greater in both the exclusive highly specialized group (P = .001) and the evolved highly specialized group (P = .02; Table 4).

Figure 2

Individual 1-way analyses of variance comparing the overuse injury distributions among the 3 specialization groups demonstrated no difference in the proportion of overuse injuries between the exclusive highly specialized (59.2%) and evolved highly specialized (53.9%) groups, whereas both groups had a higher proportion of overuse injuries than the low-moderately specialized group (45.3%).

Figure 2

Individual 1-way analyses of variance comparing the overuse injury distributions among the 3 specialization groups demonstrated no difference in the proportion of overuse injuries between the exclusive highly specialized (59.2%) and evolved highly specialized (53.9%) groups, whereas both groups had a higher proportion of overuse injuries than the low-moderately specialized group (45.3%).

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Table 4.

Injury Type Distribution Comparison Between Specialization Groups, No. (%)a

Injury Type Distribution Comparison Between Specialization Groups, No. (%)a
Injury Type Distribution Comparison Between Specialization Groups, No. (%)a

Serious overuse injuries constituted 10 of the 100 overuse injuries (10.00%) in the exclusive highly specialized group, 14 of the 133 overuse injuries (10.53%) in the evolved highly specialized group, and 32 of the 342 overuse injuries (9.36%) in the low-moderately specialized group (Figure 3). Direct comparisons between the exclusive highly specialized and evolved highly specialized groups (P = .90), exclusive highly specialized and low-moderately specialized groups (P = .85), and evolved highly specialized and low-moderately specialized groups (P = .70) revealed no differences between the groups with respect to the proportion of overuse injuries that were serious (Table 5).

Figure 3

Individual 1-way analyses of variance comparing the proportion of overuse injuries classified as serious revealed no difference in the proportion of serious overuse injuries among the exclusive highly specialized (10.0%), evolved highly specialized (10.5%), and low-moderately specialized (9.4%) groups.

Figure 3

Individual 1-way analyses of variance comparing the proportion of overuse injuries classified as serious revealed no difference in the proportion of serious overuse injuries among the exclusive highly specialized (10.0%), evolved highly specialized (10.5%), and low-moderately specialized (9.4%) groups.

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Table 5.

Comparison of Overuse Injury Severity Between Specialization Groups, No. (%)a

Comparison of Overuse Injury Severity Between Specialization Groups, No. (%)a
Comparison of Overuse Injury Severity Between Specialization Groups, No. (%)a

Multivariable Regression

Multivariable regression analysis of all 3 groups (Table 6) demonstrated that, compared with the reference group of low-moderately specialized athletes, exclusive highly specialized athletes (OR = 1.56; 95% CI = 1.10, 2.21) and evolved highly specialized athletes (OR = 1.36; 95% CI = 1.01, 1.82) were more likely to have overuse injuries than acute injuries. Compared with male sex, female sex was associated with overuse injuries relative to acute injuries (OR = 1.75; 95% CI = 1.38, 2.23). The same was true for higher age (OR = 0.89; 95% CI = 0.82, 0.95).

Table 6.

Multivariable Analysis of Overuse Injury Proportions in All 3 Specialization Groupsa

Multivariable Analysis of Overuse Injury Proportions in All 3 Specialization Groupsa
Multivariable Analysis of Overuse Injury Proportions in All 3 Specialization Groupsa

Regression analysis of data from the 2 highly specialized groups (Table 7) showed that the specialization group (evolved versus exclusive) was not associated with an increased proportion of overuse injuries. Athletes specializing in individual sports were at 1.95 times increased odds of having overuse injuries relative to acute injuries when compared with athletes specializing in team sports (95% CI = 1.17, 3.24). Among highly specialized athletes, the overuse injury proportion was not associated with sex, age, specialization path (evolved versus exclusive), age at specialization (when they started training for their main sport >8 months per year), or months of rest per year from organized sports. A validation regression model (Table 8), including only variables shown to be significantly associated with the overuse injury proportion in bivariate analyses (sex, age, starting age of training >8 months per year, and sport type), also indicated that only sport type had a statistically significant association with an increased proportion of overuse injuries, as individual-sport athletes were at 1.86 times greater odds of having overuse injuries relative to acute injuries (95% CI = 1.15, 3.00).

Table 7.

Multivariable Analysis of Overuse Injury Proportions in the Highly Specialized Groupsa

Multivariable Analysis of Overuse Injury Proportions in the Highly Specialized Groupsa
Multivariable Analysis of Overuse Injury Proportions in the Highly Specialized Groupsa
Table 8.

Multivariable Analysis of Overuse Injury Proportions in the Highly Specialized Groups Only Among Variables Individually Associated With the Overuse Injury Proportiona

Multivariable Analysis of Overuse Injury Proportions in the Highly Specialized Groups Only Among Variables Individually Associated With the Overuse Injury Proportiona
Multivariable Analysis of Overuse Injury Proportions in the Highly Specialized Groups Only Among Variables Individually Associated With the Overuse Injury Proportiona

This is the first study to compare injury patterns between 2 types of highly specialized athletes: those who quit other sports to focus on a main sport (evolved) and those who have only ever played a single sport (exclusive). We found no differences in the distribution of injury types (acute, overuse, serious overuse) between exclusive highly specialized athletes and evolved highly specialized athletes. This outcome does not support our first hypothesis, as our results suggest that high specialization, regardless of the path taken, is associated with a greater proportion of overuse injuries compared with athletes who were low-moderately specialized. Further research is needed to investigate potential differences in other injury characteristics between these 2 types of highly specialized athletes, including comparing the proportions of different types of overuse injuries (eg, bone versus soft tissue). For example, injury patterns between these groups may vary based on whether the sport relies on repetitive motions (eg, swimming, volleyball) or has a more varied movement pattern (eg, basketball, soccer).

These findings are important because they suggest that injury patterns among exclusive highly specialized athletes are more likely to be similar to those of evolved highly specialized athletes than to those of low-moderately specialized athletes, which is the category to which the exclusive highly specialized athletes would have been assigned according to the commonly used 3-question specialization score.13  These results support the suggestion by Miller et al19  to modify the 3-question scale by adding a question to account for athletes who have only ever played a single sport. This finding has implications for future authors who aim to evaluate the effects of youth sport specialization.

Both groups of highly specialized athletes had higher proportions of overuse injuries than did low-moderately specialized athletes. These outcomes were similar to those of previous studies that demonstrated a greater likelihood of overuse injuries in highly specialized athletes compared with low or moderately specialized athletes,13,16,18  though the “highly specialized” group of athletes in these studies would have represented only the evolved highly specialized population.

Sex Differences

As we are the first to delineate the unique characteristics of this exclusive highly specialized population, no prior research has been conducted on its demographic characteristics. The proportion of female athletes was highest in the exclusive highly specialized group, followed by the evolved highly specialized group, and then the low-moderate group (Table 1). Post et al25  observed that female athletes might be more likely to be highly specialized than their male counterparts, and our study further informs this suggestion in showing that highly specialized female athletes may also be less likely to have played other sports before specializing. Gender differences in sport type may be responsible; for example, the majority of highly specialized gymnasts (78 of 102) in this study were female. Gymnastics often requires year-round training starting at a young age, and Root et al26  noted that youth gymnasts often exceeded the training volume guidelines set by the American Academy of Pediatrics, which may not leave these athletes with sufficient time to participate in other organized sports. Additionally, the post hoc analysis of sport type and months of rest per year demonstrated that individual-sport athletes rested for fewer months per year than team-sport athletes, which offers another potential explanation for why these athletes may be more likely to specialize, as having less time off to rest may not lend itself to participating in multiple organized sports.

Age at Specialization

Exclusive highly specialized athletes began to train intensively (>8 months per year) for their main sport at a younger age than did evolved highly specialized athletes (Table 2). This factor may reflect the typical training schedule of the athlete’s chosen sport, as individual-sport athletes have reported greater training volume than those in team sports,17  and the authors26  of 1 study determined that more specialized gymnasts had been participating in the sport for longer than their low-specialized counterparts. Thus, their ability to participate in other sports at a younger age would be limited, and those who begin their sports experience with a single sport may therefore have more time to devote to training in that sport compared with those who start their athletic experience sampling a variety of sports.

Team- Versus Individual-Sport Differences

Pasulka et al17  demonstrated that individual-sport athletes may be more likely to specialize than team-sport athletes. Our work corroborated this, as we identified a higher proportion of athletes playing individual sports in the exclusive highly specialized group compared with the evolved highly specialized group (Table 3). Hence, children in team sports may be more likely to play multiple sports before choosing to focus on one, whereas individual-sport athletes are more likely to specialize in the first sport they play at an organized level. Although high specialization is no longer unique to individual sports such as gymnastics and figure skating,27  a difference in training philosophy between individual and team sports may exist: among the highly specialized groups, individual-sport athletes in our study rested for fewer months per year than team-sport athletes. As a consequence, especially in the context of individual-sport athletes reporting greater training volume than team-sport athletes,17  these sports may consume more of an athlete’s schedule and therefore lend themselves to exclusive specialization.

Serious Overuse Injuries

Unlike prior investigators, we observed no difference in the proportion of serious overuse injuries between highly specialized athletes and low-moderately specialized athletes. The risk factors for serious overuse injury may be related to the specific sport (eg, stress fractures in cross-country athletes) rather than the degree of specialization or path to high specialization.

Multivariable Regression

Among this population of injured athletes presenting to a sports medicine clinic, multivariable analysis reaffirmed that high specialization (both evolved and exclusive) was independently associated with greater odds of the injury being due to overuse.

Though prior researchers determined that injured adolescent athletes were, on average, older than their uninjured counterparts,13  we analyzed overuse injuries as a proportion of total injuries rather than as a proportion of the population as a whole and showed that, independent of other factors, older athletes had a lower proportion of overuse injuries than younger athletes. This differs from the findings of Stracciolini et al,28  who established that 13- to 17-year-old athletes had a greater proportion of overuse injuries than 5- to 12-year-old athletes; however, these results are not directly comparable, as Stracciolini et al28  categorized patients into 2 age brackets (5–12 and 13–17 years), whereas we analyzed age as a continuous variable. The regression also affirms the results of the prior analyses in this study: high specialization, regardless of the path taken (exclusive versus evolved), was associated with increased odds of sustaining an overuse injury (Table 6).

Female sex was also independently associated with greater odds, when presenting to clinic with an injury, of the injury being due to overuse, which is consistent with earlier research.16,2931  Jayanthi et al16  proposed that sex differences in the chosen sport type could be an explanation for this finding, suggesting that female athletes may be more likely to participate in individual sports or those with consistent repetitive motions and as a result be more susceptible to overuse injuries. Targeted studies are needed to test this hypothesis and investigate this, and potential other, mechanisms by which female athletes may be more susceptible to overuse injuries than their male counterparts.

When the analysis was restricted to the highly specialized athletes, only sport type was a significant predictor of proportion of overuse injuries: individual-sport athletes were at increased odds of sustaining an overuse injury when compared with team-sport athletes (Tables 7 and 8). The effects of age at presentation to clinic and gender were diminished when only the highly specialized groups were analyzed. Though this may seem to contradict prior outcomes of an increased risk of overuse injury in highly specialized young female athletes,3032  each had a different definition of highly specialized, as Leppanen et al30  and Carragher et al31  did not use the 3-point scale, and Biese et al,32  as in all sport specialization studies before this one, did not account for the exclusively highly specialized group. The regression also supported our other analyses regarding the lack of difference in overuse injury proportions between the exclusive and evolved highly specialized groups. Future sport-specific studies are necessary to determine how sport type interacts with specialization status and other factors, such as age and sex, to influence injury characteristics and susceptibility.

Limitations

Our study was conducted at a single site, which was a tertiary care pediatric sports medicine clinic, so the results may not be generalizable to the wider population of youth athletes presenting for medical care for sport-related injury. Providers in this type of clinic tend to have more patients with overuse injuries than an urgent care or emergency room setting, whose providers see more patients with acute injuries. The lack of an uninjured control group was another limitation, as the injuries were quantified as a proportion of the total injuries at a tertiary sports medicine clinic during the study period. The effects of sport specialization, sport type, age, and sex might have been different if injuries were quantified as a proportion of total athletes rather than a proportion of injured athletes. Population-based studies with a control group of uninjured athletes are needed to further explore how the pathway to becoming highly specialized may influence the injury risk and characteristics.

Additionally, similar to any research that relies on patient questionnaires to collect data, our work was subject to recall bias.1318  In an effort to mitigate this as much as possible, health care providers reviewed the patient surveys at the time of completion in the clinic for completeness and accuracy.

Another limitation was that our analysis did not address the timing of quitting other sports to focus on a main sport, which could have affected the risk for overuse injury in the evolved highly specialized group. Including the age at which athletes began training for their main sport for >8 months per year explained some of this effect, but the age at which the athlete stopped playing other sports altogether was not addressed. Future examinations of evolved highly specialized athletes targeting the specific timing of quitting other sports are needed to elucidate this effect. Also, future authors could explore whether the type of sport that athletes played before specialization (individual versus team) was associated with the overuse injury proportion, as we did not account for this.

The study population consisted of many female gymnasts, and their overrepresentation may have driven some of the results. However, the regression analysis of all 3 groups demonstrated that female athletes were at increased odds of having a greater proportion of overuse injuries when other variables were controlled, which was consistent with the current literature.

The distribution of injury types was similar between evolved and exclusive highly specialized youth athletes: both groups had a higher percentage of injuries due to overuse compared with low-moderately specialized athletes. For highly specialized athletes, playing an individual sport was associated with a higher proportion of overuse injuries than in those playing a team sport.

We acknowledge the contributions of Gina Johnson, BA, and Taylor Hartman, BS, in the collection of data for this project.

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Appendix. Sports Participation Historya

1. List all the organized sports you participate in during the course of the year.

Sport     Circle the number of months per year you spend training for each sport

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

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

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

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

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

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

2. If you listed more than one sport, do you consider one of these sports to be your “main sport” (more important to you than the others)? (circle one) If you only play one sport please skip to question 3.

No     Yes ______________ (indicate “main sport”)

3. How many months per year do you take off (ie, rest) from organized sports training and competition?

<1 1 2 3 4 5 6 7 8 9 10 11

If you listed only one sport above ORidentified one as yourmain sportplease answer questions49:

4. At what age did you start playing this sport? (circle one)

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

5. If you train more than 8 months/year for this sport, at what age did you begin training >8 months/year? (circle one)

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

6. On a scale of 0 to 5, how important are sports in your life?

     0 1 2 3 4 5

7. Circle the number that indicates how much you enjoy participating in practices for your sport.

No enjoyment     Most Enjoyment

0 1 2 3 4 5 6 7 8 9 10

8. Circle the number that indicates how much you enjoy participating in games/competitions for your sport.

No enjoyment     Most Enjoyment

0 1 2 3 4 5 6 7 8 9 10

9. List all other sports you previously played and circle the age when you started and stopped playing each sport.

Sport     Age when you started and stopped playing each sport

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

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

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

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

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

10. Did you quit other sports to focus on your main sport?

Yes     No

11. Do you or your team consistently participate in an active warm-up before practices and/or games?

Yes     No

12. If yes, does your active warm-up include strengthening exercises such as jumps, hops, planks, squats, lunges, push-ups, etc?

Yes     No

a Instrument is presented in its original format.

Author notes

Authors Patrick F. Murday, MD, and Daniel E. McLoughlin, BA, contributed equally to this work.