The Influence of Lower Extremity Muscle Fatigue on Baseball Pitching Biomechanics and Performance

Abstract

THE INFLUENCE OF LOWER EXTREMITY MUSCLE FATIGUE ON BASEBALL PITCHING BIOMECHANICS AND PERFORMANCE By Jeremy Praski July 2024

Director of Thesis: Nicholas Murray, PhD Major Department: Department of Kinesiology

Baseball pitching is a complex and dynamic movement involving the lower extremities, trunk, and upper extremities with the goal of throwing the 145 g baseball toward home plate with maximal velocity and accuracy. Previous research has shown a link between elbow and shoulder injury with increased pitch volume, innings pitch in a calendar year, pitch type, and number of months pitched per year (21,32). According to Spotrac, which records the injured list of MLB players and their salaries while on the injured list, 18,369 days were missed by MLB pitchers on the injury list with a throwing-related injury in 2019, which translates into $318,667,058 lost by MLB clubs (35). To date, multiple studies that have investigated the influence of fatigue on pitching kinetics, kinematics, and muscle activation in the different phases of the pitching motion (2,3,8, 24,27,28). However, none of these studies consider the performance aspects of pitching accuracy as well as pitching velocity in a simulated baseball pitching performance in which joint kinematics and muscle fatigue are also recorded. PURPOSE: The purpose of this study is to determine how lower extremity fatigue with increased pitch count impacts a pitcher’s joint kinematics, muscle activation levels, and pitching performance so that coaches may better be able decide when to take a pitcher out of a game. METHODS: Eleven high school and collegiate pitchers (age: 16.67  0.86 years, height: 1.78  0.08 m, weight: 74.6  14.82 kg) with 11.4  1.59 years of experience participated, two of which had to be excluded due to EMG issues. Data were collected using Noraxon Ultium Lab EMG, IMU, and Ninox 120 video camera. EMG electrodes were equipped to muscle bellies of the stride leg (BF, GAST, SEMI, VL, VM) and drive leg (GM, VL, VM) muscles, with IMU’s being equipped to the stride leg (shank and thigh) and throwing shoulder (upper arm and forearm), along with C7. After a warmup, participants were equipped with EMG and performed MVIC testing, and then equipped with IMU. IMU were then calibrated, and participants were given the opportunity to thrown warmup pitches off the mound. Participants threw 14-18 pitch innings with fastball, offspeed, and breakingball randomized like a game scenario. Participants threw a minimum of 60 pitches with a maximum of 105 pitches thrown. After each inning, participant rating of perceived exertion (RPE) was recoded. RESULTS: Participants averaged 80 ± 13 total pitches and had a pitch velocity of (fastball 73.29 ± 5.98 mph, 73.76 ± 6.08 mph, offspeed 66.30 ± 5.98 mp, 66.41 ± 6.25 mph, and breakingball 62.81 ± 5.44 mph, 62.87 ± 5.63 mph) and pitch accuracy of (fastball 41.17 ± 25.48%, 37.63 ± 19.67%, offspeed 38.71 ± 30.87%, 28.77 ± 19.43%, and breakingball 30.24 ± 21.70%, 28.90 ± 20.86%) for the first and last innings respectively. Shoulder external rotation for the follow through phase of the pitching motion was significantly different from the first to last inning (p=0.03). There were no other variables that were found to be significantly different from first to last inning CONCLUSION: From the first to last inning, participant median frequency (Hz) for EMG did not significantly change, thus we do not believe that their lower extremity muscles were fatigued. However, we did notice that with no lower extremity fatigue, there were moderate Cohen’s D for effect size of the Wind Up and SFC pitching phase for throwing shoulder external rotation. This would indicate that although there was so significant difference, in the Wind Up and SFC phases there were moderate differences in the mean from first to last inning. Overall, this suggests that future studies should investigate how many pitches it takes for a pitcher to fatigue.