Current Concepts in Arm Care Exercise Programs and Injury Risk Reduction in Adolescent Baseball Players: A Clinical Review

Abstract

Context:

Awareness of important injury risk factors associated with excessive pitching volume has been highlighted in the literature, but injury rates remain high. Shoulder pain in baseball players is associated with various changes in musculoskeletal movements, which presents as measurable impairments throughout the kinetic chain. Baseball coaches and rehabilitation professionals have utilized exercise programs targeting strength and flexibility of the throwing arm to prevent injuries. The purpose of this review is to summarize the current evidence regarding the effectiveness of arm care exercise programs in reducing upper extremity injury rates in adolescent baseball players.

Evidence Acquisition:

A search of electronic databases, including CINAHL with full text, MEDLINE, and SPORTDiscus was conducted to retrieve available articles in English from the years 2010 through 2020. The search terms injury prevention, exercise, and adolescent baseball were used.

Study Design:

Clinical review.

Level of Evidence:

Level 4.

Results:

Improving shoulder internal rotation range of motion by stretching the posterior shoulder muscles daily was associated with a 36% risk reduction of shoulder and elbow injuries. Group-based arm care exercise programs that target multiple musculoskeletal impairments demonstrated an approximately 50% reduced risk of elbow injury.

Conclusion:

For adolescent baseball players, arm care injury prevention programs focusing on important musculoskeletal impairments are effective at reducing injury incidence rates. Multimodal injury prevention programs that improve multiple musculoskeletal impairments are more comprehensive and may result in better injury reduction than programs focusing on a singular impairment.

The relationship between overhead throwing and upper extremity injury in adolescent baseball players continues to be a concern for health care providers.^19,29,32 Nearly 50% of adolescent baseball pitchers report pain in the shoulder or elbow while throwing during the season³¹ and the frequency of ulnar collateral ligament reconstructions has disproportionately increased in adolescents compared with collegiate or professional level pitchers.^21,30 After substantial efforts from researchers, pitching volume has been shown to be a fundamental risk factor for throwing-related injuries.^{1,28,40,42,51} Despite injury prevention efforts, such as pitching volume reduction, the overall upper extremity injury rate in adolescent baseball players has not been substantially reduced over the past decade. Although, between the 2004-2005 and 2014-2015 seasons, the annual incidence of shoulder injuries declined from 2.07 to 1.39 per 10,000 athletic exposures (AEs) and elbow injuries increased from 0.84 to 1.06 per 10,000 AEs, these trends are not statistically different.⁵²

Although the awareness of important injury risk factors associated with excessive pitching volume has been highlighted, injury rates remain high.^15,18 Volume-related risk factors include high pitch counts,^14,28,29,37 pitching greater than 8 months per year,^40,43 playing on multiple teams,^8,37 showcases,^8,67 pitching with arm pain or fatigue,^29,37,40,64 and throwing greater than 100 innings per season.¹⁸ Pitching volume guidelines such as Pitch Smart exist to protect pitchers from overuse and excessive arm fatigue.³⁴ However, compliance rates with these guidelines are typically underwhelming^17,24,41,66 and pitch counts have demonstrated inconsistent results in achieving injury risk reduction.² Thus, solely focusing on pitch volume management is likely not sufficient for effective injury prevention.³³

Baseball coaches and sports medicine professionals have recommended and utilized exercise programs targeting strength and flexibility of the throwing arm in an attempt to prevent injuries.^12,33,45,58 These arm care exercise programs vary considerably but they follow 4 principles: (1) identify risk factors, (2) define cutoff values for the risk factors based on normative data, (3) assessment and reassessment procedures that are reliable and valid, and (4) preventative exercise programs should be implemented.¹²

More recently, researchers have begun to investigate if proper management of specific physical impairments could result in injury risk reduction.^{19,49,50,57,58} Theoretically, managing risk factors could result in decreased injury rates and associated time lost from sport. However, we are not aware of any literature reviews that analyze whether injury prevention programs affect injury rates in adolescent baseball players. Therefore, the purpose of this clinical review is to summarize the current evidence regarding the value of arm care exercise programs at reducing injury incidence in adolescent baseball players.

Arm Care Injury Prevention Programs

Musculoskeletal limitations or inefficiencies throughout the kinetic chain can result in excessive physiological stress in the throwing arm.^3,9,53 To address these deficiencies, arm care exercise programs have been developed^49,50,57,63 to improve strength, dynamic stability, and range of motion (ROM) of the muscles and joints important to the throwing motion and related to shoulder and elbow health in overhead athletes.⁶³ Historically, arm care exercise programs began as generalized upper body strengthening or targeted stretching to a particular muscle group. More recently, these programs have evolved to target multiple physical impairments throughout the kinetic chain and used screening to individualize program design. However, to date there are a limited number of prospective clinical trials that have explored the effectiveness of arm care exercise programs at reducing injury risk in overhead athletes.^49,50,57

Upper Extremity Strengthening

The benefit of including shoulder strengthening exercises in arm care programs for injury risk reduction is unclear in the literature among high level of evidence (LOE) studies.³⁹ In a prospective cohort (LOE 2), Shitara et al⁵⁶ identified that external rotator weakness, measured as a ratio between dominant and nondominant arms, was associated with up to 7.3 increased odds for injury in high school baseball players. However, other high-quality evidence, 2 LOE 2^20,48 and 1 LOE 3,⁵⁹ have not supported decreased absolute shoulder strength or external rotator strength ratio as injury risk factors in adolescent baseball players. According to Sakata et al,⁴⁸ deficits in external rotation (ER), serratus anterior, or lower trapezius strength ratios were related to elbow injury in youth baseball players. Likewise, Tyler et al⁵⁹ reported that preseason deficits in shoulder ER, internal rotation (IR), or supraspinatus weakness were unrelated to upper extremity injury in high school baseball players. However, inconsistencies in testing setup position may have contributed to the variation seen in these results. Specifically, Tyler et al measured shoulder ER in a supine position and reported the absolute strength deficit whereas Sakata et al⁴⁸ and Shitara et al⁵⁶ measured ER weakness in prone and reported the ratio of ER and IR weakness.

The Thrower’s Ten exercise program is a commonly used shoulder and elbow strengthening program,^60,62 which has been recommended as an injury prevention program.^13,44,45 The program is based on electromyographic data that implicate specific exercises to best achieve meaningful muscle activation and strengthening of the shoulder girdle and elbow musculature.^44,46 The Thrower’s Ten program and more recently the updated Advanced Thrower’s Ten exercise program⁶³ has been found to improve key performance metrics important to baseball pitchers, such as shoulder strength and endurance³⁶ and pitching velocity.¹⁶ However, the ability of the Thrower’s Ten to reduce injury risk appears to be unknown. To date, no published studies have investigated injury risk reduction outcomes associated with the Thrower’s Ten or Advanced Thrower’s Ten exercise programs in baseball players. Further research is needed to quantify the degree to which shoulder strength deficits contribute to injury risk and explore if the Thrower’s Ten program can decrease injury incidence in baseball pitchers.

Shoulder Stretching

As one of the most commonly studied areas, shoulder mobility deficits or adaptations to throwing are commonly observed and may be risk factors for injury. Restricted shoulder IR mobility limits energy transfer to the throwing arm during the pitching motion and requires greater effort to maintain throwing velocity, which could increase stress on the upper extremity.¹⁰ The presence of glenohumeral internal rotation deficit (GIRD) has been associated with biomechanical faults in high school pitchers, such as larger trunk tilt and less trunk rotation.¹⁰ A dominant-side GIRD has been proposed as an injury risk factor in overhead throwers.^4,5,23 Shanley et al⁵⁵ (LOE 2), found that high school baseball players who had GIRD of greater than 25° in their dominant shoulder were at nearly 5 times (risk ratio [RR] 4.8; 95% CI, 2.1-11.3) greater risk for injury. It appears that GIRD may be an important musculoskeletal adaptation in baseball pitchers and proper management with posterior shoulder stretching can reduce upper extremity injury risk.

In a prospective cohort (LOE 2), Shitara et al⁵⁷ examined the outcome of an injury prevention program in reducing shoulder and elbow injury risk over the course of a competitive baseball season (150 days) in 92 high school baseball pitchers. This study compared the difference in incidences of upper extremity injury defined as ≥8 days of disability between shoulder self-stretching for GIRD and external rotator strengthening for rotator cuff weakness. Stretching the posterior shoulder muscles daily by performing the “sleeper stretch” to improve shoulder IR ROM was associated with a 36% (hazard ratio [HR], 0.355; 95% CI, 0.133-0.947) shoulder and elbow injury risk reduction.⁵⁷ The overall incidence of shoulder and/or elbow injury for pitchers who performed posterior shoulder stretching compared with pitchers who did not was 25% (n = 8/32) and 57% (n = 8/14), respectively. Additionally, time-to-event analysis showed that pitchers who performed daily sleeper stretching were able to pitch 3 times longer throughout the season compared with those who did not perform daily preventive stretching.⁵⁷ Although rotator cuff weakness has been suggested as an injury factor for high school pitchers,^56,59 Shitara et al⁵⁷ found that posterior shoulder stretching alone was more effective than the addition of external rotator strengthening at reducing incidence of injury.

Multimodal Group Arm Care Program

More recently, arm care programming has expanded beyond the narrow focus of 1 or 2 injury risk factors by evolving into comprehensive programs that target multiple impairments throughout the entire body. Throwing a baseball is a full-body movement pattern and requires appropriate linkage between the upper and lower body.³ Several studies have evaluated the overhead thrower from a biomechanical perspective and determined that appropriate kinetic linking is necessary for optimal performance and decreased injury risk.^3,9,11,35,53 Important musculoskeletal deficits that have been identified as potential injury risk factors for adolescent baseball players include GIRD,^55,56 total range of motion (TROM),⁴⁹ decreased hip IR ROM,^49,50 poor thoracic posture,^48,49 and deficits in single-leg balance.⁶⁵ Arm care programs focusing on full body strength and ROM maintenance are likely more advantageous for injury prevention because they address multiple risk factors or impairments.^8,40,61

Preventative programs which target multiple known risk factors have shown promise in improving physical impairments and reducing injury rates in youth baseball players.^49,50 Two high-quality prospective studies have been published delineating the effectiveness of an injury prevention program in youth baseball players.^49,50 In a 2018 nonrandomized controlled trial (LOE 2), Sakata et al⁴⁹ reported a 49.2% (HR, 50.8%; 95% CI, 0.29-0.88) reduction in the incidence of medial elbow pain in 305 youth baseball players after a preventative program targeting strength and ROM of the shoulders, hips, and spine. The injury prevention program, called the Yokohama Baseball-9 (YKB-9), was performed 2 times per week and consisted of a total of 18 exercises (9 strengthening and 9 stretching) designed to improve multiple risk factors throughout the kinetic chain. Improvement of physical injury risk factors resulted in an incidence of 0.8 per 1000 AEs in the athletes who performed the prevention training compared with 1.7 per 1000 AEs in those who did not participate. Multivariate logistical regression identified improvement in shoulder TROM, decreased thoracic kyphosis angle, and increased lead hip IR ROM as the most important musculoskeletal impairments associated with predicting success in preventing elbow injuries.⁴⁹ These findings are consistent with other research that has implicated decreased TROM, poor thoracic spine ROM, and limited hip IR ROM as important impairments that could increase risk for injury. In a 2018 systematic review and meta-analysis, Bullock et al⁴ reported that shoulder TROM less than 160° and asymmetries greater than 10° were both associated with increased injury risk. In an LOE 2 study, an increased thoracic kyphosis angle of greater than 30° was associated with a 2-fold increased risk for injury in youth baseball players.⁴⁸ Limited hip IR ROM, which seems remote to the throwing shoulder, has also been associated with increased risk for development of medial elbow pain.^47,48

In 2019, the original YKB-9 program was modified to be less complex and time intensive. The modified YKB-9 (mYKB-9) program reduced the number of exercises from 18 to 9, but still consisted of (1) stretching for the elbow, shoulder, and hip; (2) dynamic mobility for the scapula and thorax; and (3) lower body balance.⁵⁰ The effectiveness of the mYKB-9 program was evaluated in a clustered randomized controlled trial (LOE 2) at reducing elbow and shoulder injuries in a cohort of 237 youth baseball players.⁵⁰ At 12-month follow-up, the incidence of shoulder/elbow injuries was significantly lower in the athletes who completed the mYKB-9 program compared with those who did not participate (HR, 1.94; 95% CI, 1.17-3.2). Specifically, those who did not participate in the mYKB-9 program were nearly 2 times more likely to experience an upper extremity injury. Furthermore, there was a 48.5% reduction in risk for shoulder or elbow injury associated with participating in the mYKB-9 program compared with the control group. This reduction in overuse elbow injury is consistent with the results found by Sakata et al⁵⁰ in 2019.

Compared with the original YKB-9, the mYKB-9 program, which included half as many exercises, resulted in an overall adherence rate improvement from 57.4% (n = 78/136) to 73.4% (n = 89/109). Additionally, athletes who demonstrated high adherence with the injury prevention program had 0.5 per 1000 AEs incidence of elbow injury compared with 1.2 per 1000 AEs in those who had low adherence.⁵⁰ The simplification of mYKB-9 program greatly improved adherence while not compromising effectiveness, suggesting that fewer but more targeted exercises can still achieve similar reductions in injury incidence.

Screening for Musculoskeletal Impairments

The arm care exercise programs in this clinical review show promise at reducing injury risk in adolescent baseball players, but the independent risk factors are also important when designing these preventative programs. Researchers have previously studied preseason movement-based screens in high school and collegiate baseball players as a way to predict injury risk.^6,7,25 Poor performance on the Functional Movement Screen (FMS) shoulder mobility test was associated with an adjusted odds ratio of 5.14 (95% CI, 1.14-22.9) of having an overuse injury during the preseason.⁷ Additionally, poor performance on the Selective Functional Movement Assessment upper extremity pattern tests were associated with increased odds of overuse symptoms. Specifically, identified dysfunction in either the unilateral shoulder extension/IR pattern or the unilateral shoulder flexion/ER pattern was associated with an adjusted odds ratio of 6.10 (95% CI, 1.22-30.5) and 17.07 (95% CI, 13.9-210.2) during both the preseason and the competitive season, respectively.⁷ However, these screening procedures are limited to only the shoulder and do not consider other important musculoskeletal impairments, specifically the thorax, hips, and dynamic balance.

Individualized-Group Arm Care Programs

Injury risk is multifactorial^48,49,56 and since each individual baseball player could possess unique impairments, it seems logical to individualize arm care programs to maximize benefit. Shoulder pain in overhead athletes is commonly associated with various musculoskeletal movement changes, which can present as measurable impairments in the upper and lower quarter, but may manifest differently in each player.^3,27,54 In general, group-based programs are limited in depth by only focusing on single risk factors or specific injuries.³⁸ The 48.5% injury incidence reduction as seen in mYKB-9 is encouraging, but there still remains room for improvement, as a large proportion of baseball players still sustained an overuse injury.⁵⁰ Individualized arm care programs could address multiple musculoskeletal impairments such as shoulder strength and ROM, thoracic spine mobility, hip ROM, and balance. Appropriate distribution of exercises based on the need of the player could potentially create a better avenue for greater injury risk reduction.

In an LOE 2 study, Huebner et al²² found that 50% of high school soccer players were able to advance from “high” to “low” risk based on the Move2Perform injury risk categorization algorithm²⁶ after an 8-week individualized injury prevention program. Lehr et al²⁶ validated the Move2Perform software as an injury risk algorithm that takes into consideration current pain, previous injury history, FMS performance, and Y Balance Test–Lower Quarter asymmetries and composite score relative to an individual’s age, gender, and sport. Individuals who were classified into the “high-risk” category were at a 3.4 (RR, 3.4; 95% CI, 2.0-6.0) times increased risk for future injury.²⁶ Using preseason screening, Huebner et al assigned a combination of 3 strengthening and stretching exercises that were performed during the warm-up and cooldown based on the individual’s FMS score. The remaining components of the program consisted of a group-based plyometric, agility, and core training program that was similar for all athletes.²² Interestingly, individuals who reported pain during screening were unlikely to make a categorical improvement. This suggests that when screening produces pain, a group-based program is not individualized enough to reduce injury risk and appropriate referral to a health care provider for a detailed assessment should be considered.

Limitations

This literature review is not without limitations. First, the conclusions of this review are based on the results of the limited number of prospective arm care exercise studies that have evaluated injury incidence reduction as an outcome measure. Although limited in quantity, the studies reviewed demonstrate a high level of evidence and are representative of the current scientific knowledge base in adolescent baseball. Second, individualized group programming has only preliminary evidence on effectiveness and has not been explored in baseball players. Finally, this review focused exclusively on adolescent baseball players. Therefore, the conclusions of this review may not be generalizable to other baseball players at the collegiate or professional level.

Conclusion

For adolescent baseball players, performing arm care exercises for injury prevention that focus on important musculoskeletal impairments are effective at reducing injury incidence rates. Injury prevention programs that focus on a singular musculoskeletal risk factor, such as posterior shoulder stretching, are effective but may not be comprehensive enough to obtain ideal injury reduction because they fail to consider throwing injuries as multifactorial. Adolescent baseball players, especially pitchers, should be encouraged to perform a multimodal arm care exercise program that incorporates localized posterior shoulder stretching and normalizing shoulder TROM, thoracic spine mobility, and hip IR ROM to best prevent throwing-related injury.