Stride Leg Ground Reaction Forces Pre- and Post-Fatigue in Collegiate Baseball Pitchers
Creators: name: Alley, Courtney 
Publisher: name: University of Nevada, Las Vegas
Year: 2017

description: Context: Baseball pitching requires the coordination of the lower and upper extremities to effectively generate and transfer force to the ball. High-velocity pitchers have been found to have significantly greater stride leg force generation than low-velocity pitchers. The influence of stride leg fatigue on pitching has yet to be investigated. Objective: The purpose of this study was to examine the effect of stride leg fatigue on peak vertical ground reaction forces (vGRFs) and hand velocity. Design: Pretest-posttest. Setting: Biomechanics laboratory. Patients or Other Participants: A convenience sample of 11 collegiate baseball pitchers (19.27 ± 0.64 years old; 85.88 ± 12.16 kg; 1.84 ± 0.07 m; eight right-handed, three left-handed) volunteered. To be included, participants needed to be listed as a pitcher on a collegiate baseball roster without reported injuries to the upper or lower extremity that resulted in decreased training volume during the fall baseball season. Interventions: Simultaneous three-dimensional kinematic (200 Hz; Vicon Motion System Ltd., Oxford,UK) and kinetic data (1,000 Hz, Kistler Inc., Amherst, NY, USA) were collected. Participants utilized a self-selected, competition-style warm-up. Retro-reflective markers were placed on bony landmarks of the stride leg, trunk, and throwing arm. Participants threw maximal effort fastballs into a net placed 5.0 meters from the portable pitching mound's rubber. Participants were positioned so that the stride leg foot landed on the force platform. After 10 rested-state pitches, participants performed a fatigue protocol of stride leg Bulgarian split squats at 60 beats/minute for maximum repetitions. One-minute rest was given between each of the four sets. Following the fatigue protocol, participants threw 10 fatigued-state maximal effort pitches. Main Outcome Measures: Outcome measures included peak vGRFs of the stride leg and hand velocity at release. The means of valid trials (minimum of seven) were used for analyses. Peak vGRFs were reported as body weight [BW=GRF/(kg·9.81m/s2)]. One-tailed, paired t-tests (? = 0.05) were utilized to test for statistical significance between rested and fatigued conditions and a Pearson product-moment correlation were used to examine the relationship between vGRFs and hand velocity. Statistics were computed in SPSS. Results: Participants completed 81.36 ± 21.94 total Bulgarian split squat repetitions and reported an RPE score of 7.82 ± 1.60. Paired t-tests revealed significant decrease (p = 0.005) between peak Fz1 vGRF values in rested-state (1.57 ± 0.49 BW) compared to fatigued-state (1.31 ± 0.62 BW). Hand velocity in the rested-state (23.32 ± 1.60 m/s) was significantly (p=0.004) higher than fatigued-state (22.61 ± 1.55 m/s), but not functionally relevant. Peak vGRF and hand velocity at release were not significantly correlated in either condition (rested-state Fz1: r = 0.162, p = 0.318; Fz2: r =.151, p = 0.329; fatigued-state Fz1: r = 0.228, p = 0.250; Fz2: r = 0.277, p = 0.410). Conclusions: Peak vGRFs Fz1 and hand velocity decreased when the stride leg fatigued to a level of statistical significance. Due to the small sample size, the variable does warrant future investigation. Increased understanding of the influence of the stride leg upon pitching endurance and performance could influence rehabilitation and training programs.