Forearm Pronation at Foot Contact: A Biomechanical Motion-Capture Analysis in High School and Professional Pitchers.

Background: It has previously been speculated that baseball pitchers who display excessive forearm pronation at foot contact (FC) have a higher propensity toward ulnar collateral ligament injury and subsequent surgery. Purpose: To evaluate the association between degree of forearm pronation/supination at FC and throwing arm kinetics in high school and professional pitchers, at both the individual (intrapitcher) and the group (interpitcher) level. Study Design: Descriptive laboratory study. Methods: High school (n = 41) and professional (n = 196) pitchers threw 8 to 12 fastballs while being assessed with a 3-dimensional motion-capture system (480 Hz). Pitchers at each playing level were divided into a supination or pronation subgroup depending on degree of forearm pronation at FC. Regression models were built to observe the relationship between forearm pronation at FC and kinetic and kinematic parameters of interest. Results: At both the individual and the group level of high school and professional pitchers, there was no significant correlation between forearm pronation at FC and elbow varus torque (P min = .21). For every 10° increase in forearm pronation at FC in the individual high school pitcher, elbow flexion at FC decreased by 5°, whereas maximum elbow extension velocity was achieved 0.6% later in the pitch. In addition, elbow medial force increased by 4.1 N and elbow varus torque increased by 0.8 N·m for every 10° increase in forearm supination at FC. For every 10° increase in forearm supination in the individual professional pitcher, ball velocity increased by 0.5 m/s, shoulder external rotation at FC decreased by 11°, and elbow medial force decreased by 5.5 N. Conclusion: Supination- or pronation-predominant forearm motion during the pitch did not significantly differ between playing levels. Excessive forearm pronation at FC was not a significant risk factor for increased throwing arm kinetics for high school or professional pitchers. There was a weak positive association between forearm supination at FC and elbow varus torque in the individual high school pitcher. Ultimately, coaches and pitchers may be better served by redirecting their focus to other mechanical aspects of the pitch that may have stronger associations with injury risk implications as well as performance.

Interval Throwing Programs at Distances Beyond 150 Feet Can Be Equivalent to Pitching Over Five Innings.

PURPOSE: To determine the cumulative elbow varus torque (EVT) experienced during created interval throwing programs (ITP) and derive innings pitched equivalent for each step. METHODS: High school pitchers wearing the motusBASEBALL sensor who had at least 50 throws at 90, 120, 150, and 180 ft and game pitches were included in this analysis. Means for EVT per throw and torque per minute were calculated at each distance. Three throwing programs were created using a template of 1 phase at each distance with 2 steps per phase. Programs varied only by number of throws per set (20, 25, and 30 throws for Program A, B, and C, respectively). Total EVT for each step, phase, and program were calculated using mean EVT per throw at each distance. Total EVT for each step and program were converted to a mean inning pitched equivalent (IPE) and maximum pitch count equivalent (MPE), respectively, using in-game pitching torque values and expected mean pitch counts (15 pitches/inning and maximum 105 pitches/game). RESULTS: In total, 3,447 throws were analyzed from 7 subjects (16.7 years ± 0.8 years). EVT per throw increased at each distance (range 36.9-45.5 N·m), comparable to game pitches (45.7 N·m). Mean EVT per minute was highest for 90 ft throws (193.4 N·m/min) and lowest for game pitches (125 N·m/min). Throwing Program A had the lowest range of IPE (Step 1: 2.0 and Step 8: 3.7), and Program C had the highest range (Step 1: 3.0 and Step 8: 5.6). The phases of Program A never exceeded 1MPE. Program B exceeded this threshold after Phase 1, and Program C exceeded 1MPE at every phase. Total program MPE ranged from 3.5 to 5.2 (Program A and C, respectively). CONCLUSIONS: Programs requiring 25 or more throws per set reached approximately 5 IPE per day. Increasing throwing repetitions by 10 throws resulted in a nearly 50% increase in IPE and MPE. LEVEL OF EVIDENCE: IV, retrospective cohort study.

Increased Shoulder Distraction Force and Shoulder Horizontal Abduction in Professional Baseball Pitchers With Discordant Torso Rotation Order.

BACKGROUND: Inefficient energy transfer from the pelvis and trunk has been shown to increase compensation at the level of the shoulder. Kinetic chain sequencing of the core segments is underexamined in professional baseball pitchers, especially as it relates to changes in upper extremity kinetics. PURPOSE: To evaluate elbow and shoulder kinetics in a cohort of professional pitchers differentiated by instances of discordant pelvic to upper torso sequencing during the pitch. STUDY DESIGN: Descriptive laboratory study. METHODS: 285 professional baseball pitchers were evaluated using 3D motion capture (480 Hz). Pitchers were divided into "chronological" and "discordant" groups based on whether maximum pelvic rotation velocity occurred before (chronological) or after (discordant) maximum upper torso rotation velocity during the pitch motion. Pelvic, upper torso, and shoulder kinematic parameters, shoulder distraction force, shoulder internal rotation torque, and pitch efficiency (PE) were compared between groups. RESULTS: Pitchers with discordant torso sequencing (n = 30; 110 pitches) had greater shoulder horizontal adduction at maximum external rotation (mean difference, 3.6°; 95% CI, -5.2° to -2.0°; t = -4.5; P < .001) and greater maximum shoulder external rotation (mean difference, 3.7°; 95% CI, 5.7° to 1.5°; t = -3.5; P < .001) than chronological pitchers (n = 255; 2974 pitches). PE did not differ between groups (P = .856), whereas ball velocity was significantly faster in the discordant group (mean difference, 0.6 m/s; 95% CI, -1.1 to -0.3 m/s; t = -3.3; P = .0012). Chronological pitchers had significantly reduced shoulder distraction force (mean difference, -4.7% body weight (BW); 95% CI, -7.9% to -1.5% BW; t = -2.9; P = .004) with no difference in shoulder internal rotation torque (P = .160). These kinematic and kinetic differences were not observed when accounting for interpitcher variability. CONCLUSION: Between pitchers, those who had a discordant pelvic to upper torso sequence experienced significantly greater shoulder distraction forces, potentially compensating by increasing maximum shoulder external rotation and horizontal abduction. Achieving maximal pelvic rotation velocity before maximal rotation velocity may be advantageous in preventing compensation at the upper extremity and excessive throwing arm loading. CLINICAL RELEVANCE: Identifying risk factors for increased upper extremity forces has potential implications in injury prevention. Specifically, mitigating shoulder distraction forces may be beneficial in reducing risk of injury.

Association of Pitch Timing and Throwing Arm Kinetics in High School and Professional Pitchers.

BACKGROUND: Understanding the relationship between the temporal phases of the baseball pitch and subsequent joint loading may improve our understanding of optimal pitching mechanics and contribute to injury prevention in baseball pitchers. PURPOSE: To investigate the temporal phases of the pitching motion and their associations with ball velocity and throwing arm kinetics in high school (HS) and professional (PRO) baseball pitchers. STUDY DESIGN: Descriptive laboratory study. METHODS: PRO (n = 317) and HS (n = 54) baseball pitchers were evaluated throwing 8 to 12 fastball pitches using 3-dimensional motion capture (480 Hz). Four distinct phases of the pitching motion were evaluated based on timing of angular velocities: (1) Foot-Pelvis, (2) Pelvis-Torso, (3) Torso-Elbow, and (4) Elbow-Ball. Peak elbow varus torque, shoulder internal rotation torque, and shoulder distraction force were also calculated and compared between playing levels using 2-sample t tests. Linear mixed-effect models with compound symmetry covariance structures were used to correlate pitch velocity and throwing arm kinetics with the distinct temporal phases of the pitching motion. RESULTS: PRO pitchers had greater weight and height, and faster ball velocities than HS pitchers (P < .001). There was no difference in total pitch time between groups (P = .670). PRO pitchers spent less time in the Foot-Pelvis (P = .010) and more time in the Pelvis-Torso (P < .001) phase comparatively. Shorter time spent in the earlier phases of the pitching motion was significantly associated with greater ball velocity for both PRO and HS pitchers (Foot-Pelvis: B = -6.4 and B = -11.06, respectively; Pelvis-Torso: B = -6.4 and B = -11.4, respectively), while also associated with increased shoulder proximal force (Pelvis-Torso: B = -76.4 and B = -77.5, respectively). Decreased time in the Elbow-Ball phase correlated with greater shoulder proximal force for both cohorts (B = -1150 and B = -645, respectively) with no significant correlation found for ball velocity. CONCLUSION: Significant differences in temporal phases exist between PRO and HS pitchers. For all pitchers, increased time spent in the final phase of the pitching motion has the potential to decrease shoulder distraction force with no significant loss in ball velocity. CLINICAL RELEVANCE: Identifying risk factors for increased shoulder and elbow kinetics, acting as a surrogate for loading at the respective joints, has potential implications in injury prevention.

The association of stride length to ball velocity and elbow varus torque in professional pitchers.

Professional basebal pitchers (n =315) were divided into quartiles based on increasing stride length and random intercept linear mixed-effect models were used to correlate stride length with ball velocity, pelvis and trunk rotation at foot contact, and throwing arm kinetics. Average stride length among all pitchers was 78.3±5.3%body height (%BH). For every 10% increase in stride length, ball velocity increased by 0.9 m/s (B =0.089, ß =0.25, p <0.001) and trunk rotation initiation occurred 4.23 ms earlier (B =-0.42, ß =-0.14, p <0.001). When divided into quartiles pelvis rotation was less towards home plate in Q1 compared to Q3 and Q4 (70.0±10.7° vs. 60.9±8.9° and 58.6±9.1°, p <0.001). No significant differences in shoulder internal rotation torque (p =0.173) or elbow varus torque (p =0.072) were noted between quartiles. Professional baseball pitchers who reached stride lengths of 80%BH or greater achieved faster ball velocity without an increase in elbow varus torque. This may, be a byproduct of rotating the pelvis for a greater proportion of the pitching motion and thereby more effectively utilising the lower extremities in the kinetic chain. Encouraging players to achieve this threshold of stride length may enhance ball velocity outcomes.