The purpose of this study was to determine the relationship between ground reaction force (GRF) variables to jump height, jump time, and the Reactive Strength Index (RSI). Twenty-six Division I male soccer players performed three maximum effort CMJs on a dual-force platform system that measured three-dimensional kinetic data. The trial producing peak jump height was used for analysis. Vertical GRF (Fz) variables were divided into unloading, eccentric, amortization, and concentric phases and correlated to jump height, RSI (RSI= Jump height/jump time), and jump time (from start to takeoff). Significant correlations were observed between jump height and RSI, concentric kinetic energy, peak power, concentric work, and concentric displacement. Significant correlations were observed between RSI and jump time, peak power, unload Fz, eccentric work, eccentric rate of force development (RFD), amortization Fz, amortization time, 2nd Fz peak, average concentric Fz, and concentric displacement. Significant correlations were observed between jump time and unload Fz, eccentric work, eccentric RFD, amortization Fz, amortization time, average concentric Fz, and concentric work. In conclusion, jump height correlated to variables derived from the concentric phase only (work, power, and displacement), while Fz variables from the unloading, eccentric, amortization, and concentric phases correlated highly to RSI and jump time. These observations demonstrate the importance of countermovement Fz characteristics for time-sensitive CMJ performance measures. Researchers and practitioners should include RSI and jump time with jump height to improve their assessment of jump performance.
Copyright (C) 2017 by the National Strength & Conditioning Association.