Abstract
Background and Hypothesis
There is increasing concern about the role sport specialization might play in the increasing injury rates observed among youth baseball pitchers. However, existing research on specialization in baseball has focused on high school and professional baseball populations. We hypothesized that pitchers who were highly specialized, reported pitching more than eight months in the past year, received private coaching, or pitched with pain or fatigue in the previous year would report worse throwing-arm health.
Methods
One-hundred eighty-four Little League pitchers (boys N = 181, age 9.8 ± 1.6 years old) between 7 and 12 years of age completed an anonymous, online questionnaire with their parents’ assistance. The questionnaire consisted of participant demographics, sport specialization status, months of pitching per year, whether they traveled regularly to participate in showcases, if they received private coaching, whether they pitched with elbow or shoulder pain, whether they pitched with fatigue, and the Youth Throwing Score (YTS), a valid and reliable patient-reported outcome measure for youth baseball players. The associations between variables of interest and YTS were examined using multivariable linear regression, adjusting for covariates.
Results
Sport specialization, pitching year-round, and receiving private coaching were not associated with the YTS (P > .05). Pitching with pain in the previous year was associated with a worse YTS score than pitching without pain (least square mean [standard error]: 49.6 [1.8] vs. 57.8 [1.1], P < .001). Similarly, pitching with fatigue in the previous year was associated with worse YTS scores (least square mean [standard error]: 52.1 [1.4] vs. 55.3 [1.3], P = .01). Pitchers who reported traveling regularly for showcases scored worse on the YTS compared with those who did not travel regularly for showcase events (least square mean [standard error]: 51.0 [2.0] vs. 56.4 [0.9], P = .01).
Conclusions
Pitching with pain or fatigue was associated with worse throwing-arm health in Little League baseball pitchers. While traveling at least once a month to participate in showcases was also associated with worse throwing-arm health, specialization and private coaching were not related to worse throwing health. Clinicians working with pediatric patient populations should be aware that while the factors examined in this article were reported relatively infrequently, screening for Little League pitchers who participate in showcases or pitch with pain or fatigue may be an effective strategy for identifying these individuals who are at higher risk of injury.
Keywords: Shoulder, Elbow, Pediatric sports medicine, Injury prevention, Baseball
More than 4 million children between the ages of 6 and 12 years participated in youth baseball in 2018.31 Pitching has been identified as a baseball position that presents unique risks for injury among youth and professional baseball players. A recent meta-analysis concluded that being a pitcher was a significant risk factor for elbow injury in youth baseball players.1 Owing to the increasing incidence of ulnar collateral ligament sprains among youth players and the immense burden represented by throwing-related injuries at all levels of baseball, there has been a significant amount of research focused on identifying injury risk factors among youth baseball pitchers. Previously identified risk factors for injury among youth pitchers include excessive pitching volume (pitches per game or innings per year), pitch velocity, deficits in shoulder range of motion or strength, age, and arm fatigue.1,3,17,26
Across youth sports generally and within the youth baseball community specifically, there has been increasing concern regarding year-round intensive focus in a single sport at the exclusion of other sports, also known as sport specialization.15,32 While sport specialization has been identified as a risk factor for lower extremity overuse injuries among athletes from a variety of sports, there has been limited research examining the potential risks of specialization among baseball pitchers.4 Findings from several studies examining year-round pitching as a risk factor for injury among adolescent pitchers have been equivocal.7,18,30 A series of magnetic resonance imaging studies among asymptomatic Little League baseball athletes found that year-round baseball participation, specialization in baseball, and private coaching were associated with elbow or shoulder magnetic resonance imaging abnormalities.11,12,20,21,24 To our knowledge, there have been no reported findings on the association of specialization with injury specifically among Little League pitchers, which may be partially attributed to the difficulties inherent in collecting reliable injury data in younger populations.
Therefore, the purpose of this article was to determine whether factors related to sport specialization were associated with throwing-arm health among Little League baseball pitchers. We hypothesized that pitchers who were highly specialized reported pitching more than eight months in the past year, received private coaching, or pitched with pain or fatigue in the previous year would report worse throwing-arm health.
Materials and methods
Participants
This study was approved by the Institutional Review Board at San Diego State University. Twelve Little League organizations in Southern California were recruited to send e-mails between June and December 2019 to parents whose children participated in their organization. Parents received an e-mail with a link to an anonymous, online questionnaire for their child to complete. To participate in the study, the child had to have been between the ages of 7 and 12 years and had to have participated on an organized baseball team in the previous 12 months. The requirement for signed informed consent was waived owing to the anonymous nature of the survey, but by reading the informational page at the start of the questionnaire and choosing to continue, participants were considered to have provided consent. Parents were encouraged to help their child complete the survey in case their child had any questions. Of the 246 Little League athletes who completed the questionnaire, 184 (74.7%) indicated that they had pitched for their team in the previous year and were included in the study’s final analysis.
Questionnaire
The questionnaire consisted of three sections: (1) participant demographics (including age, sex, and year in school), (2) baseball participation information (including primary baseball position, sport specialization status, and baseball participation volume), and (3) the Youth Throwing Score (YTS). The questionnaire was designed to be completed in less than 10 minutes and was written at a Flesch-Kincaid Grade Level of 2.9.
Participants were classified as either low, moderate, or highly specialized using a validated specialization Jayanthi scale that was recently modified to improve its accuracy.16 Throwing-arm health was assessed using the YTS, a validated and reliable 14-item outcome measure for youth baseball players.2 The YTS was originally developed to provide a tool to assess the upper extremity health of younger baseball players via self-report.2 Responses on the YTS generated a score between 14 and 70, with higher scores indicating better arm health.2 Participants were asked whether they traveled overnight regularly (at least once a month) for baseball showcases, if they received coaching outside of their Little League team, and to indicate the number of months in the previous year that they played baseball and the number of months that they pitched. Participants were also asked whether they had ever pitched with elbow or shoulder pain in the previous year and if they had pitched with fatigue during the past year. Finally, participants were asked to provide the number of innings they had pitched in the previous year, and the average number of pitches they threw during a typical game. As only 101 of the pitchers (54.9%) responded to these final two questions, these two variables were only presented in the univariate analyses and not included in the final regression analysis.
Statistical analysis
Data were summarized using means and standard deviations, medians and interquartile ranges, and frequencies and proportions (%). Univariate parametric analyses (independent t-tests, one-way analyses of variance) and bivariate correlations (Pearson’s r) were used to examine mean differences and associations of YTS based on variables of interest. Cohen’s d effect sizes (ES) were calculated with 95% confidence intervals (95% CIs) for differences in YTS between categorical variables, with ES < 0.20 considered a small effect, ES = 0.50 considered a medium effect, and ES > 0.80 considered a large effect.14
Multivariable linear regression was used to examine the association between variables of interest and YTS. Least square mean (LS-Means) estimates with standard errors (SE) were calculated for the variables of interest from the linear regression model, adjusting for covariates. Selection of factors to include in the model consisted of any variable that was significant in the univariate analysis. The final model consisted of specialization status, age, regular travel for showcases, pitching with pain in the previous year, and pitching with fatigue in the previous year. The multivariable linear regression model was assessed to determine whether it met the assumptions of linear regression using the Global Validation of Linear Models Assumptions package19 in R and via visual inspection of quantile-quantile and residual plots. Comparisons of LS-Mean estimates of YTS between levels of the variables of interest were conducted using post hoc pairwise Tukey’s honestly significant difference tests. Statistical significance was set at 2-sided a priori P < .05, and all analyses were performed in R statistical software (R Foundation for Statistical Computing, Vienna, Austria).
Results
One-hundred eighty-four Little League pitchers (boys N = 181, age 9.8 ± 1.6 years) completed the questionnaire. Participant demographics and sport participation characteristics are presented in Table I. Approximately 1 in five (20.8%) participants reported that pitching was their primary baseball position. Only 15.8% of the pitchers were classified as highly specialized and only 16.4% reported pitching more than eight months in the previous year. Approximately 1 in ten (9.8%) pitchers reported pitching with pain in the previous year, while 1 in four (26.1%) pitchers reported pitching with fatigue in the previous year.
Table I.
Participant demographics and sport participation characteristics (N = 184).
| Variable | N (%), mean (SD), or median (IQR) |
|---|---|
| Sex | |
| Male | 181 (98.4%) |
| Female | 3 (1.6%) |
| Age | 9.8 (1.6) |
| Baseball start age | 5.3 (1.6) |
| Years of baseball participation | 4.5 (2.0) |
| Mo/Y of organized baseball | 7.8 (2.7) |
| Primary position | |
| Pitcher | 38 (20.8%) |
| Catcher | 37 (20.2%) |
| First base | 26 (14.2%) |
| Second base | 23 (12.6%) |
| Shortstop | 26 (14.2%) |
| Third base | 13 (7.1%) |
| Outfield | 20 (10.9%) |
| Specialization scale | |
| Low | 86 (46.7%) |
| Moderate | 69 (37.5%) |
| High | 29 (15.8%) |
| Youth Throwing Score (YTS) | 60.4 (8.0) |
| Travel overnight regularly for showcases | |
| Yes | 13 (7.1%) |
| No | 171 (92.9%) |
| Receive private coaching outside of League | |
| Yes | 70 (38.0%) |
| No | 114 (62.0%) |
| Pitched >8 mo per y | |
| Yes | 30 (16.4%) |
| No | 153 (83.6%) |
| Pitched with pain in previous y | |
| Yes | 18 (9.8%) |
| No | 166 (90.2%) |
| Pitched with fatigue in previous y | |
| Yes | 48 (26.1%) |
| No | 136 (73.9%) |
| Innings pitched in previous y∗ | 25 [9-41] |
| Average pitches per game in previous y∗ | 41.4 (18.4) |
Includes responses from only N = 101 participants.
Univariate differences in YTS based on categorical baseball participation variables are presented in Table II. Highly specialized athletes scored significantly worse on the YTS compared with low specialization athletes (57.0 ± 9.2 vs. 61.4 ± 7.9, P = .03). There were no significant differences in YTS between pitchers who reported pitching as their primary position and those who did not, between those that reported receiving private coaching and those who did not, or between those that reported pitching year-round in the last year and those who did not (P > .05). Pitchers who reported traveling regularly for showcases had worse scores on the YTS than those who did not travel regularly for showcases (53.6 ± 10.4 vs. 61.0 ± 7.6, P = .03). Pitchers who reported pitching with pain sometime in the previous year had worse scores on the YTS compared with those who did not pitch with pain (50.3 ± 6.6 vs. 61.5 ± 7.3, P < .001). Similarly, those who reported pitching with fatigue in the previous year had worse scores than those who did not (55.9 ± 7.5 vs. 62.0 ± 7.6, P < .001).
Table II.
Univariate differences in YTS based on categorical baseball participation characteristics.
| Variable | Youth Throwing Score, mean (SD) | Effect size (95% CI) | P value |
|---|---|---|---|
| Specialization | 0.4 [−0.03 to 0.8] | .03 | |
| Low | 61.4 (7.9) | ||
| Moderate | 60.7 (7.3) | ||
| High | 57.0 (9.2) | ||
| Pitcher primary position | 0.1 [−0.3 to 0.4] | .74 | |
| Yes | 60.1 (8.6) | ||
| No | 60.6 (7.9) | ||
| Regular travel for showcases | 0.7 [0.2 to 1.3] | .03 | |
| Yes | 53.6 (10.4) | ||
| No | 61.0 (7.6) | ||
| Private baseball coaching | 0.1 [−0.2 to 0.4] | .45 | |
| Yes | 59.9 [7.9] | ||
| No | 60.8 [8.0] | ||
| Pitch >8 mo | 0.1 [−0.3 to 0.5] | .62 | |
| Yes | 59.8 [8.0] | ||
| No | 60.6 [8.0] | ||
| Pitched with pain in previous y | 1.7 [1.2 to 2.2] | <.001 | |
| Yes | 50.3 [6.6] | ||
| No | 61.5 [7.3] | ||
| Pitched with fatigue in previous y | 0.8 [0.5 to 1.2] | <.001 | |
| Yes | 55.9 [7.5] | ||
| No | 62.0 [7.6] |
YTS, Youth Throwing Score; SD, standard deviation; CI, confidence interval.
Correlations of continuous baseball participation characteristics with YTS are presented in Table III. Increased age (Pearson’s r [95% CI]: −0.16 [−0.30 to −0.02], P = .03), increased innings pitched in the previous year (Pearson’s r [95% CI]: −0.23 [−0.41 to −0.04], P = .02), and increased average pitches thrown per game (Pearson’s r [95% CI]: −0.27 [−0.44 to −0.08], P = .01) were all associated with worse YTS scores. Pitchers’ age was also positively correlated with innings pitched in the previous year (Pearson’s r [95% CI]: 0.37 [0.19 to 0.53], P < .001) and with average pitches per game (Pearson’s r [95% CI]: 0.44 [0.26 to 0.59], P < .001).
Table III.
Correlations of continuous baseball participation characteristics with YTS.
| Variable | Pearson’s r (95% CI) | P value |
|---|---|---|
| Age | −0.16 (−0.30 to −0.02) | .03 |
| Baseball start age | −0.12 (−0.26 to 0.02) | .09 |
| Yr of baseball participation | −0.02 (−0.16 to 0.13) | .79 |
| Mo/Y of pitching | −0.10 (−0.24 to 0.05) | .20 |
| Innings pitched in previous y∗ | −0.23 (−0.41 to −0.04) | .02 |
| Average pitches per game in previous y∗ | −0.27 (−0.44 to −0.08) | .01 |
YTS, Youth Throwing Score; CI, confidence interval.
Includes responses from only N = 101 participants.
After adjusting for all other factors in the model, the multivariate model indicated that pitching with pain in the previous year was associated with a worse YTS score (LS-Means [SE]: 49.6 [1.8] vs. 57.8 [1.1], P < .001) (Table IV). Similarly, pitching with fatigue in the previous year was associated with a worse YTS score (LS-Means [SE]: 52.1 [1.4] vs. 55.3 [1.3], P = .01). Pitchers who reported traveling regularly for showcases scored worse on the YTS compared to those who did not (LS-Means [SE]: 51.0 [2.0] vs. 56.4 [0.9], P = .01). No significant associations were found between age or sport specialization status with YTS after adjusting for all other factors in the model (P > .05).
Table IV.
Least square mean estimates for YTS based on multivariate linear regression∗.
| YTS least squares mean estimate (SE) | P value | |
|---|---|---|
| Sport specialization scale | ||
| Low | 54.6 (1.4) | .97† |
| Moderate | 54.3 (1.4) | .37‡ |
| High | 52.2 (1.6) | .26§ |
| Regular travel for showcases | ||
| Yes | 51.0 (2.0) | .01 |
| No | 56.4 (0.9) | |
| Pitched with pain in previous y | ||
| Yes | 49.6 (1.8) | <.001 |
| No | 57.8 (1.1) | |
| Pitched with fatigue in previous y | ||
| Yes | 52.1 (1.4) | .01 |
| No | 55.3 (1.3) |
YTS, Youth Throwing Score.
Adjusted R2 for model: 0.24.
Model includes specialization, age, regular travel for showcases, pitching with pain in previous year, and pitching with fatigue in previous year.
Comparison between low and moderate specialization categories.
Comparison between moderate and high specialization categories.
Comparison between low and high specialization categories.
Discussion
The primary findings of this article were that pitching with fatigue or pain and traveling regularly for showcases were associated with worse throwing-arm health in Little League pitchers. No associations were observed between specialization and year-round pitching with throwing-arm health. To our knowledge, this is the first study to directly examine the association of factors related to sport specialization with a valid and reliable patient-reported measure of throwing-arm health in preadolescent baseball pitchers.
Significant research attention has been directed recently toward the topic of specialization in youth sports.4,6,15 Among a wide range of youth sports, specialization has been repeatedly identified as a risk factor for lower extremity overuse injuries.4,10,22,27 This has resulted in a number of medical organizations and sport-governing bodies, including USA Baseball and Major League Baseball, to recommend that youth athletes delay specializing in a single sport for as long as possible.5,6,8,15,32 However, the evidence regarding the risks of specialization has been more mixed in studies of baseball athletes. In particular, there have been conflicting results between studies of adolescent baseball players as to whether pitching year-round is a risk factor for injury.7,18,30 The results of our study indicated that there were no significant differences in YTS between pitchers who reported pitching year-round vs. those who did not pitch year-round in the previous year.
There has been limited research among youth baseball using more formal methods of classifying specialization status, such as the Jayanthi specialization scale. A recent study of high school baseball players found that highly specialized pitchers were more likely to report a previous throwing arm overuse injury and scored worse on the YTS compared with low specialization athletes.23 In contrast, we found no significant differences in YTS based on specialization status after adjusting for covariates. Additional research is needed to determine why these results differed between high school and Little League pitchers. We theorize that the physical effects of specialization may not manifest until the athlete is older. We also suggest that highly specialized high school pitchers may simply have more opportunities to pitch than Little League pitchers and therefore have increased throwing volume, potentially resulting in fatigue and injury.
Receiving private coaching in the previous year was not associated with throwing-arm health, but traveling at least once a month for showcases was associated with lower (worse) scores on the YTS. In a study of 26 asymptomatic Little League baseball players, Pennock et al21 found that working with a private coach was associated with abnormal MRI findings in the throwing elbow. The difference between this result and our findings may be attributed to the high variability in private coaching quality. Although not assessed in our study, we suggest that high-quality coaching may reduce the likelihood of injury, whereas lower-quality coaching may increase the risk of injury. Therefore, until additional studies can better examine this relationship (eg, assess if certain methods used by coaches are more effective to reduce elbow or shoulder injury), whether or not the use of a private coach may help to minimize a youth pitcher’s injury risk remains unclear.
In a study of Little League baseball players, Register-Mihalik et al25 reported that travel and showcase participation was associated with arm pain and injury, while a more recent study of high school baseball players by Post et al23 found no association between regular travel for showcase participation and throwing-arm health. Our results are in agreement with the study of Little League athletes by Register-Mihalik et al25 and suggest that showcase participation at an early age may raise a youth baseball pitcher’s risk of injury. Recent discussion regarding sport specialization has highlighted the fact that specialization behavior is likely different between various sports and that the Jayanthi specialization scale may not be the most accurate measure of specialization for all sports.13 Owing to the unique aspect of showcase participation in baseball as a venue for highly competitive teams or athletes, it is possible that frequent travel for showcase participation may be a better marker of specialized sport behavior among youth baseball athletes than other measures of specialization, such as the Jayanthi scale.
Two recent systematic reviews concluded that pitching with fatigue17 and a history of pitching with pain1 are clear risk factors of injury in youth baseball. We also found that both factors were associated with lower (worse) scores on the YTS, even after adjusting for all potential covariates. Furthermore, in the univariate analysis, pitching with pain and pitching with fatigue in the previous year both demonstrated large effect sizes in YTS differences between groups. As a result of the increasing burden of elbow injuries, specifically ulnar collateral ligament sprains, at all levels of baseball, significant research efforts have been dedicated to identifying risk factors for injury.9,29 These potential risk factors have included physical factors or adaptations, training volume or workload, sport and baseball participation history, and biomechanical factors.1,3,26,28 Our results, in combination with the studies examined in the systematic reviews previously indicated, suggest that asking whether the youth athlete has pitched with pain or fatigue may represent a simple screening question for identifying athletes at greater risk of injury that would benefit from an individualized injury prevention program.
We acknowledge several limitations in our study. The primary limitation of this study is that we used a cross-sectional study design. Therefore, we cannot establish causality between our variables of interest and throwing-arm health. However, owing to the limited amount of data regarding sport specialization in preadolescent baseball pitchers, we felt that this limitation was acceptable in efforts to increase our ability to assess a larger sample (ie, nearly 200) of Little League pitchers. Second, we only surveyed athletes from Little League organizations in Southern California. Therefore, our results may not be representative of Little League athletes nationwide and from different backgrounds. In addition, we encouraged parents to assist their child in completing the survey, which may have resulted in the child not answering honestly on all aspects of the survey. However, we felt that most participants would not find the questions too sensitive and that having the parents to help clarify any question may provide more valid answers. We also felt that having the parent assist the participant allowed us more access to investigate a younger population that has not been extensively examined in the sport specialization literature. Unfortunately, only half of the pitchers were able to provide a response regarding their number of innings in the previous year and average pitches per outing and therefore that data were not able to be included in the final regression analysis. This is likely a result of the young age of our participants and having to rely on parents to assist their child in responding to the questionnaire. Finally, we were not able to calculate a response rate owing to our survey distribution methodology. All surveys were distributed by the 12 Little League administrators to parents in their organization. We felt that having the administrators send out the survey would improve our credibility with members of that organization. However, this also meant that we did not have direct control over the exact number of individuals who had access to the survey.
Conclusion
Traveling at least once a month to participate in showcases and pitching with either pain or fatigue were all associated with worse throwing-arm health in Little League pitchers. Specializing in baseball, pitching year-round, and receiving private coaching were not associated with throwing arm health. Clinicians working with pediatric patient populations should be aware that while the factors examined in this article were relatively rare, screening for Little League pitchers who participate in showcases or pitch with pain or fatigue may be an effective strategy for identifying these high risk individuals.
Conflicts of interest
The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
Funding
This study was supported by a grant that was funded by the Far West Athletic Trainers’ Association, but this sponsor played no role in study design, collection/analysis/interpretation of data, writing of the manuscript, and decision to submit the manuscript for publication.
Footnotes
This study was approved by the Institutional Review Boards at San Diego State University. (Study HS-2019-0107).
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