Date

11-13-2025

Department

School of Health Sciences

Degree

Doctor of Philosophy in Health Sciences (PhD)

Chair

Joshua Dexheimer

Keywords

countermovement jump, force plate, neuromuscular output, exit velocity, bat speed, athlete monitoring, performance variability

Disciplines

Kinesiology | Medicine and Health Sciences

Abstract

This dissertation explored the use of countermovement jump (CMJ) force plate metrics as indicators of neuromuscular status and their relationship to hitting performance variability across a competitive season in professional baseball. Although there is an increase in the integration of sports science and performance analytics in professional sports, a significant gap remains in longitudinal, in-season monitoring models that connect neuromuscular adaptations to hitting-specific outputs, such as bat velocity and ball exit velocity (BEV). This study examined lower-body force production as measured by uniaxial bilateral force plates and how they interact with hitting output task demands over time. Using a longitudinal observational design with correlational and predictive components, this study tracked force plate-derived variables, including peak power, concentric impulse, modified reactive strength index (mRSI), and force at zero velocity (FV0). The sample consisted of 55 professional baseball hitters from the Washington Nationals Baseball Club across the 2023 and 2024 seasons. Weekly CMJ assessments were conducted using V ALD ForceDecks uniaxial bilateral force plates, totaling 6,211 individual jump tests. Hitting performance data, including bat speed, ball exit velocity, home runs, slugging percentage, and batting average, were collected using Hawk-Eye Innovations tracking systems. Data analysis included Pearson correlations, multiple regression models, repeated measures ANOVA, and k-means cluster analysis. Results revealed significant correlations between all CMJ metrics and hitting outcomes, with Peak Power demonstrating the strongest relationships (r = 0.298 to .523, p < 0.01). Multiple regression models displayed 15.8-38.9% of variance in hitting performance, with the strongest predictive capability for exit velocity (R² = .389, p < .001). Four distinct neuromuscular archetypes were identified, with Power-Speed athletes demonstrating superior performance across power-based metrics. Progressive seasonal declines in neuromuscular capabilities were observed, with Peak Power decreasing 6.2% and mRSI declining 6.6% from early to late season. Players maintaining CMJ metrics above individualized baselines for more than 80% of the season exhibited 39% lower performance variability and 55% fewer performance declines. Two-week declines in Peak Power ≥150W significantly predicted subsequent performance decrements with 73% accuracy. The findings further reinforce CMJ metrics as reliable indicators of hitting performance variability in professional baseball, with differential relationships between neuromuscular capabilities and power-based versus contact-based outcomes.

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