Background and hypothesis: Sport specialization is increasingly common in youth sports and is a risk factor for lower-extremity overuse injuries. However, limited data exist on whether specialization is associated with upper-extremity (UE) overuse injuries, specifically in youth baseball players. We hypothesized that specialization in baseball and being a pitcher would be associated with poorer arm health and UE overuse injury history in the previous year. Methods: During the 2019 spring baseball season, 551 high school baseball athletes (aged 15.9 +/- 1.3 years) from 3 states (Alabama, n =200; California, n=188; and Michigan, n=163) completed an anonymous questionnaire. Athletes were recruited from 5 high schools in each state, with schools matched based on factors that influence specialization rates. The questionnaire consisted of (1) demographic characteristics, (2) baseball participation information (including sport specialization status), and (3) throwing-arm health and UE injury history in the previous 12 months. Throwing-arm health was assessed using the Youth Throwing Score (YTS), a validated and reliable outcome measure for youth baseball players. Multivariate regression analyses were used to examine the association between variables of interest and the YTS or UE overuse injury history, adjusting for covariates. Results: After adjustment for covariates, highly specialized athletes were more likely to report a UE overuse injury in the previous year compared with low-specialization athletes (odds ratio [OR], 3.77; 95% confidence interval [CI], 1.39-10.2, P=.009). Both athletes who reported playing baseball for more than 8 months per year (OR, 2.03; 95% CI, 1.12-3.65; P=.019) and athletes who reported being a pitcher (OR, 2.11; 95% CI, 1.20-3.72; P=.010) were more likely to report a history of UE overuse injury. Highly specialized players reported lower (worse) YTS values compared with low-specialization players (least-squares mean estimate +/- standard error, 56.5 +/- 1.1 vs. 53.3 +/- 0.7; P=.034). Players who reported pitching as one of their positions scored worse on the YTS than non-pitchers (leastsquares mean estimate +/- standard error, 51.6 +/- 0.8 vs. 57.2 +/- 0.6; P <.001). Conclusion: Although baseball recommendations that discourage sport specialization are widely available for parents, athletes, and coaches, high rates of sport specialization were reported in our sample. We found that being highly specialized in baseball was associated with UE overuse injury history and worse throwing-arm health in high school baseball athletes. Continued education for baseball parents, athletes, and coaches is necessary to raise awareness of the risks associated with high specialization. Level of evidence: Level III; Cross-Sectional Design; Epidemiology Study (C) 2020 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.

Context: Lateral ankle sprains commonly occur in an athletic population and can lead to chronic ankle instability. Objective: To compare ankle strength measurements in athletes who have mechanical laxity and report functional instability after a history of unilateral ankle sprains. Design: Retrospective cohort. Setting: Athletic Training Research Lab. Participants: A total of 165 National Collegiate Athletic Association Division I athletes, 97 males and 68 females, with history of unilateral ankle sprains participated. Main Outcome Measures: Functional ankle instability was determined by Cumberland Ankle Instability Tool scores and mechanical ankle instability by the participant having both anterior and inversion/eversion laxity. Peak torque strength measures, concentric and eccentric, in 2 velocities were measured. Results: Of the 165 participants, 24 subjects had both anterior and inversion/eversion laxity and 74 self-reported functional ankle instability on their injured ankle. The mechanical ankle instability group presented with significantly lower plantar flexion concentric strength at 30 degrees/s (139.7 [43.7] N.m) (P =.01) and eversion concentric strength at 120 degrees/s (14.8 [5.3] N.m) (P =.03) than the contralateral, uninjured ankle (166.3 [56.8] N center dot m, 17.4 [6.2] N.m, respectively). Conclusion: College athletes who present with mechanical laxity on a previously injured ankle exhibit plantar flexion and eversion strength deficits between ankles.

Early sport specialization is a growing concern because it may lead to repetitive stress and excessive joint loading. Current data indicate that early specialization leads to injury, but its role in producing underlying tissue changes has not been examined. PURPOSE: To determine effects of sport specialization on upper extremity tissue characteristics. METHODS: Seventy-five collegiate baseball, softball, and tennis players (36 male, 39 female; age = 19.8 ± 1.4 years, height = 175.3 ± 10.4 cm; weight = 76.0 ± 13.9 kg) participated. Subjects completed surveys and were grouped based on age when they chose a primary sport and started competing for more than 8 months/year. Shoulder range of motion was measured with an inclinometer. Posterior capsule thickness, humeral retrotorsion, and ulnar collateral ligament (UCL) thickness were collected via ultrasound. For each measurement, non-dominant arm values were subtracted from dominant arm. Data were analyzed with hierarchical multiple regression, which determined group differences while controlling for sport played. RESULTS: Sport specialization criteria were met by 21 athletes before age 11 (Early), 28 athletes between the ages of 11-14 (Middle), and 25 athletes age 15 or older (Late). Shoulder internal (Early = -9.7 ± 5.6°; Middle = -8.8 ± 7.0°; Late = -8.2 ± 6.2°) and external (Early = 9.6 ± 11.1; Middle = 10.4 ± 11.8; Late = 9.9 ± 8.1) rotation produced clinically significant variations bilaterally but no statistically significant group differences (Internal: R2 = .08, p = .23; External: R2 = .07, p = .26). No group differences were noted for posterior capsule thickness (R2 = .07, p = .28), humeral retrotorsion (R2 = .16, p = .07), or UCL thickness (R2 = .11, p = .09). Mean humeral retrotorsion (10.2 ± 6.1°) and UCL thickness (0.42 ± 0.61 mm) were greater on the dominant arm. CONCLUSIONS: Early sport specialization does not appear to exacerbate the bilateral tissue differences naturally present in collegiate overhead athletes. Therefore, sport specialization may be less concerning at the tissue level than the stress of overhead sport for the average athlete. Since the magnitude of tissue maladaptation associated with injury remains unknown, more data should be collected to determine connections among specialization, tissue characteristics, and injury rates in this population.

Shoulder pain in adult, overhead athletes has been attributed to a loss of glenohumeral internal rotation. However, underlying soft tissue and bony changes that alter range of motion likely contribute to pain progression. Shoulder pain can begin as early as 8 years of age in overhead athletes, but little data exists on the adaptations that potentially occur at a young age. PURPOSE: To compare range of motion and tissue adaptations in the shoulders of swimmers, baseball players, and non-overhead athletic controls ages 8-10. METHODS: 55 youth athletes; 20 swimmers (years played=3.0±1.4), 15 baseball players (years played=4.9±1.7), and 20 non-overhead athletes participated. Glenohumeral internal (IR) and external rotation (ER) were measured with a digital inclinometer. Posterior capsule thickness (PCT) and humeral twisting (retrotorsion, HR) were examined using musculoskeletal ultrasound. All measures were taken bilaterally. The dominant arm was defined as the arm preferred to throw a ball for maximum distance. Age and years played were identified as potential co-variates, but neither significantly affected statistical models. Therefore, 3x2 ANOVAs and Tukey post-hoc testing were used to analyze group and arm dominance differences. RESULTS: Interaction effects were observed for IR (p=0.03), ER (p<0.01), PCT (p=0.02), and HR (p=0.01). Youth baseball players exhibited a 9.2±9.9° IR loss and 18±10.0° ER gain on the dominant arm compared to the non-dominant arm. These IR and ER differences did not exist in swimmers or controls. The dominant arms of baseball players manifested with greater PCT (1.29±0.24mm) than the dominant arms of all other populations. A significant main effect (p<0.01) was also observed for PCT, with swimmers (1.11±0.14mm) and baseball players (1.21±0.19mm) presenting with greater PCT than control subjects (1.04±0.12mm). The non-dominant arms of baseball players demonstrated the least HR (-21.6±10.5) of all participants (swim=-11.3±6.9, non-overhead=-11.3±7.7). CONCLUSIONS: Tissue adaptation occurs in youth athletes after only 3 years of overhead sport participation and at an age earlier than previously documented. Sport selection affects the scope of these changes, with the dominant arm of baseball players undergoing the greatest adaptation. Supported by NATA REF grant 13DGP016

The anterior cruciate ligament (ACL) provides critical proprioceptive information to the brain, optimizing neuromechanical coupling and dynamic restraint to protect the knee during high velocity athletic maneuvers. Despite controversial incidence rate between limbs, the non-dominant leg has been shown to detect joint position sense as accurately as a dominant leg. It remains unclear how the brain perceives mechanical loading between limbs. PURPOSE: To examine how leg dominance influences brain activity during knee loading. METHODS: Twenty-four healthy controls (12 Males: 25.9±6.4yrs, 75.5±11.3kg, 175.6±7.6cm, 12 Females: 28.7±5.1yrs, 57.1±7.4kg, 162.6±4.7cm) with no history of knee injury volunteered. Event-related desynchronization (ERD) from electroencephalography (EEG) quantified somatosensory cortex activity while the ACL was loaded at constant force (45N/sec) anteriorly (3sec) and posteriorly (2sec). Each second of anterior loading was recorded for laxity (mm; LAX1, LAX2, LAX3), stiffness (N/mm; STIF1, STIF2, STIF3), and cortical ERD (% decreased power; ERD1, ERD2, ERD3). Comparisons were made between limbs using paired t-tests and between dependent variables using Pearson’s correlation coefficients. RESULTS: No significant main effects were observed for laxity, stiffness, and cortical activity. The relationship between LAX1 and ERD1 revealed a large, negative effect in the dominant knee (r = -.728, p = .001) but a large, positive effect in the non-dominant knee (r = .692, p = .002). A positive association between LAX2 and ERD2 was observed for dominant leg (r = .577, p = .024), representing a large effect size, while a medium effect for non-dominant leg (r = .499, p = .041). A large, positive correlation between LAX3 and ERD3 revealed for dominant leg (r = .731, p = .001) CONCLUSION: The dominant and non-dominant legs exhibit different brain responses during early loading, despite no interlimb differences in laxity and stiffness. Therefore, different sensory perceptions may exist in the brain, between limbs, as a result of joint loading. Such asymmetric somatosensory cortex activity may affect neural processing needed for muscle coordination and maintenance of knee stability. Future studies should explore the brain’s role in neuromechanical coupling to prevent musculoskeletal injury.

CONTEXT Fatigue in overhead athletes reduces shoulder muscular contraction and proprioception. These deficits may lead to alterations in scapular upward rotation, which is associated with multiple chronic shoulder conditions prevalent in tennis players. OBJECTIVE To identify the effect of a functional fatigue protocol on scapular upward rotation in collegiate male tennis players. DESIGN Randomized controlled clinical trial. SETTING Research laboratory. PATIENTS OR OTHER PARTICIPANTS Twenty healthy male tennis players with no history of shoulder injury completed this study. Participants were divided into 2 groups, experimental (age = 19.4 ± 1.1 years, height = 180.1 ± 8.9 cm, weight = 72.7 ± 11.6 kg) and control (age = 19.6 ± 1.2 years, height = 181.1 ± 6.6 cm, weight = 81.6 ± 13.5 kg). INTERVENTION(S) Participants in the experimental group performed a tennis-serving protocol until the onset of fatigue. Fatigue was defined as a participant reporting a rating of 15 on the Borg Scale of Perceived Exertion and reaching a heart rate of 70% of maximum. Instead of completing the fatigue protocol, control participants rested for an interval time matched to the experimental group. MAIN OUTCOME MEASURE(S) Scapular upward rotation of the dominant arm was measured at rest and at 60°, 90°, and 120° of glenohumeral elevation in the scapular plane. Upward-rotation measurements were taken prefatigue, postfatigue, and at 24, 48, and 72 hours postexercise. Scapular upward-rotation values were calculated as change scores from baseline and analyzed using a 2 × 4 mixed-model analysis of variance. RESULTS Significant group-by-time interaction effects were found in postfatigue change scores. The experimental group displayed scapular upward-rotation deficits at all testing positions postfatigue (rest: -2.1° ± 1.4°, 60°: -2.2° ± 2.2°, 90°: -3.2° ± 2.1°, 120°: -4.0° ± 1.3°). No differences were observed at 24, 48, or 72 hours after the fatigue protocol. CONCLUSIONS Fatigue impaired scapular upward rotation in male tennis players, but values returned to baseline within 24 hours. Clinicians should monitor scapular upward rotation in tennis players returning to competition within a day after heavy serving activity.

Context: Plyometric training is credited with providing benefits in performance and dynamic restraint. However, limited prospective data exist quantifying kinematic adaptations such as amortization time, glenohumeral rotation, and scapulothoracic position, which may underlie the efficacy of plyometric training for upper-extremity rehabilitation or performance enhancement. Objective: To measure upper-extremity kinematics and plyometric phase times before and after an 8-wk upper-extremity strength- and plyometric-training program. Design: Randomized pretest-posttest design. Setting: Research laboratory. Participants: 40 recreationally active men (plyometric group, age 20.43 +/- 1.40 y, height 180.00 +/- 8.80 cm, weight 73.07 +/- 7.21 kg; strength group, age 21.95 +/- 3.40 y, height 173.98 +/- 11.91 cm, weight 74.79 +/- 13.55 kg). Intervention: Participants were randomly assigned to either a strength-training group or a strength- and plyometric-training group. Each participant performed the assigned training for 8 wk. Main Outcome Measures: Dynamic and static glenohumeral and scapular-rotation measurements were taken before and after the training programs. Dynamic measurement of scapular rotation and time spent in each plyometric phase (concentric, eccentric, and amortization) during a ball-toss exercise were recorded while the subjects were fitted with an electromagnetic tracking system. Static measures included scapular upward rotation at 3 different glenohumeral-abduction angles, glenohumeral internal rotation, and glenohumeral external rotation. Results: Posttesting showed that both groups significantly decreased the time spent in the amortization, concentric, and eccentric phases of a ball-toss exercise (P < .01). Both groups also exhibited significantly decreased static external rotation and increased dynamic scapular upward rotation after the training period (P < .01). The only difference between the training protocols was that the plyometric-training group exhibited an increase in internal rotation that was not present in the strength-training group (P < .01). Conclusion: These findings support the use of both upper-extremity plyometrics and strength training for reducing commonly identified upper-extremity-injury risk factors and improving upper-extremity performance.

CONTEXT:The high number of repetitions and high forces associated with overhead throwing lead to anatomical adaptations, such as humeral retrotorsion and posterior-capsule thickness, in elite and professional baseball athletes. However, little is known about the origin and progression of these changes that may account for the increasing trend of chronic shoulder injuries in youth baseball and precipitate subsequent pathologic conditions throughout a young athlete's lifetime.OBJECTIVE:To investigate the relationship of age and upper extremity dominance on humeral retrotorsion, posterior-capsule thickness, and glenohumeral range of motion.DESIGN:Cross-sectional study.SETTING:Research laboratory, local baseball fields, and training facilities.PATIENTS OR OTHER PARTICIPANTS:Thirty-six boys (mean age = 10.94 ± 1.34 years, height = 151.31 ± 12.17 cm, mass = 42.51 ± 10.32 kg) ranging in age from 8 to 12 years and involved in organized youth baseball.MAIN OUTCOME MEASURE(S):Diagnostic ultrasound was used to determine humeral retrotorsion and posterior-capsule thickness. Glenohumeral internal rotation and external rotation were measured using a handheld inclinometer. We used 2 × 2 mixed-model analyses of variance to compare the influence of limb dominance and age on the dependent variables of humeral retrotorsion, posterior-capsule thickness, internal rotation, and external rotation.RESULTS:The dominant shoulders of youth throwers exhibited less glenohumeral internal rotation but greater humeral retrotorsion, posterior-capsule thickness, and glenohumeral external rotation than the nondominant shoulders. Dominant internal rotation was greater in the 8- to 10-year-old group than in the 11- to 12-year-old group, and results trended toward a difference (F1,33 = 4.12, P = .05). Correlations existed between humeral retrotorsion and range of motion (P < .05).CONCLUSIONS:The structural adaptations in the dominant shoulders of younger baseball players were similar to adaptations observed in older baseball athletes, indicating that more examination is needed in younger athletes. We are the first to demonstrate greater posterior-capsule thickness in the dominant shoulders of youth baseball athletes.

Background Strength training interventions have long been a cornerstone of ankle injury rehabilitation, with greater emphasis on the eccentric (ECC) muscle actions necessary for coordinated ankle movements. Deficits in strength between involved and uninvolved ankles typically exist following an acute ankle sprain; while these same deficits have also been implicated as a contributing factor to the development and persistence of chronic ankle instability (CAI). Objective To compare ECC isokinetic ankle strength measures between athletes with and without CAI after a history of unilateral ankle sprain. Design Cross-sectional. Setting Athletic training research laboratory. Participants A total of 135 male and female student-athletes participating in the high risk sports of football, basketball, lacrosse, soccer, field hockey, and volleyball with histories of unilateral ankle sprain. Interventions The independent variables were group classification (CAI, stable) and limb (involved, uninvolved). Subjects completed the Cumberland Ankle Instability Tool (CAIT) to define group classification with subjects scoring <25 being classified as CAI and those scoring >25 being classified as stable. Main outcome measurements ECC isokinetic peak torque (PT) values were collected using a KinCom isokinetic dynamometer during plantar flexion (PF), dorsiflexion (DF), inversion (INV), and eversion (EV) and movements at both 30˚/s and 120˚/s. 2 × 2 ANOVAs were used to compare group (CAI, stable) and limb (involved, uninvolved) for each dependent variable. Results A significant main effect was present for ECC INV at 30˚/s (p = 0.033). The uninvolved side (26.9 ± 10.9 Nm) was stronger than the involved side (25.3 ± 9.6 Nm). A trend towards significance existed for the ECC PF, with the uninvolved side appearing to be stronger at 30˚/s (229.9 ± 74.5 Nm, p = 0.095) and 120˚/s (218.4 ± 7 9.8 Nm, p = 0.106) than the involved limb (30˚/s = 223.8 ± 82.4 Nm; 120˚/s = 207.3 ± 82.0 Nm). A similar trend was observed when examining ECC INV values at 120˚/s (p = 0.100) and ECC DF at 120˚/s (p = 0.098). Interestingly, there were no significant differences between any of the group comparisons. Conclusions ECC ankle strength does not differentiate whether an athlete has CAI, but the musculature on the involved ankle appears to be weak compared to the opposite uninvolved limb. Our results add to the growing evidence suggesting that neuromuscular deficits other than strength are likely producing the chronic signs and symptoms associated with CAI.

Background: Anterior cruciate ligament injuries occur frequently in athletics, and anterior cruciate ligament injury prevention programs may decrease injury risk. However, previous prevention programs that include plyometrics use a variety of exercises with little justification of exercise inclusion. Because gluteal and hamstring activation is thought to be important for preventing knee injuries, the purpose of this study was to determine which commonly used plyometric exercises produce the greatest activation of the gluteals and hamstrings.Methods: EMG (Electromyography) amplitudes of the hamstring and gluteal muscles during preparatory and loading phases of landing were recorded in 41 subjects during 5 commonly used plyometric exercises. Repeated measures ANOVAs (Analysis of Variance) were used on 36 subjects to examine differences in muscle activation.Findings: Differences in hamstring (P <.01) and gluteal (P <.01) activities were identified across exercises during the preparatory and landing phases. The single-leg sagittal plane hurdle hops produced the greatest gluteal and hamstring activity in both phases. The 180 degrees jumps did not produce significantly greater gluteal or hamstring activity than any other exercise.Interpretation: Single-leg sagittal plane hurdle hops may be the most effective exercise to activate the gluteals and hamstrings and may be important to include in anterior cruciate ligament injury prevention programs, given the importance of these muscles for limiting valgus loading of the knee. Because 180 degrees jumps do not produce greater gluteal and hamstring activation than other plyometric exercises, their removal from injury prevention programs may be warranted without affecting program efficacy. (C) 2013 Elsevier Ltd. All rights reserved.