sports medicine

Stride Length Compensations and Their Impacts on Brace-Transfer Ground Forces in Baseball Pitchers

INTRODUCTION. “Pitching-fatigue”, considered a primary mechanism for throwing arm injuries, can impact lower body power generation to adopt compensatory stride lengths. The purpose of the study was to investigate stride length compensation impacts on brace-transfer ground reaction forces. Brace-transfer refers to the phase initiated at stride foot contact (SFC) ending at maximal external shoulder rotation (MER). We hypothesize that brace-transfer forces are affected by stride variations without impacting ball velocity. METHODS. Nineteen elite high school and collegiate baseball pitchers were randomly crossed over to throw two, 80-pitch simulated games ; (A) +25% desired stride, and (B) -25% desired stride length. Normalized stride length to body height indicated 76% and 52%, for (A) and (B), respectively. The four highest ball velocity trials per subject (Jugs Sports, Tualatin, OR) recorded by 3D kinematics software (Vicon Nexus, Oxford Metrics, UK) derived normalized propulsion and bracing ground reaction force data (Kistler Instrument Corp., Amherst, NY). Post-processing (Visual 3D, C-Motion Inc, Rockville, MD, USA) indicated SFC, MER, and peak linear throwing hand velocity at ball release (BR). RESULTS. Stride lengthening increased propulsion vertical and anterior shear impulses and posterior shear drive foot forces (p<0.001). Greater stride leg posterior shear forces occurred with increased strides (p=0.002). Ball and throwing hand velocities were not affected. DISCUSSION. Overexertion impacting stride length affects baseball pitchers’ typical propulsion and bracing strategies without impacting ball velocity. CONCLUSION. Radar velocities may not detect high effort pitches thrown consistently with altered ground reaction forces, which may lead to arm injuries.


Listed In: Biomechanics, Sports Science


Between Landing Kinetic and Kinematic Differences in a Drop Vertical Jump

ACL ruptures are catastrophic injuries that are debilitating to athletes. Specific kinematic and kinetic variables observed in landing and cutting are associated with increased ACL injury risk. The drop vertical jump (DVJ) test has been established as an ideal task to evaluate neuromuscular control and simulate motions and moments that place athletes at risk for ACL injuries. A DVJ involves an athlete landing from a 31 cm drop followed by a maximal vertical jump and subsequent landing. This study aimed to examine kinetic and kinematic differences between the first and second landing of a DVJ. 239 middle and high school athletes each performed 3 trials of a DVJ task for a 10 camera motion analysis system while landing on AMTI force platforms. Kinematic variables demonstrated a decrease in peak hip and knee flexion, hip adduction, and knee abduction angles from the first to second landing. Kinetic variables demonstrated smaller peak knee flexion, knee abduction, and hip flexion moments in the second landing. Overall, the second landing exhibited mechanics characteristic of a higher intensity athletic task or lower neuromuscular control. The second landing may serve as a better screening tool for sagittal plane risk factors, while the first landing may prove optimal for the assessment of frontal plane control and injury risk.


Listed In: Biomechanical Engineering, Biomechanics, Physical Therapy, Sports Science