Influence of countermovement depth on the countermovement jump‐derived reactive strength index modified
Alejandro Pérez‐Castilla, Jonathon Weakley, Felipe García‐Pinillos, F. Javier Rojas, Amador García‐Ramos
Abstract
Abstract This study aimed to investigate the effect of countermovement depth on the magnitude of the countermovement jump (CMJ) derived reactive strength index modified (RSI mod ), and to compare the RSI mod between the CMJ performed with a self‐preferred knee flexion angle (CMJ pref ) and the CMJ performed from a pre‐determined knee flexion angle (CMJ refer ) with the countermovement depth more similar to the CMJ pref . Sixteen subjects (11 males and 5 females; age 25.1 ± 6.3 years, body mass 69.7 ± 10.2 kg, body height 172.9 ± 8.1 m) randomly performed in a single session the CMJ pref and CMJs from five pre‐determined knee flexion angles (60°, 75°, 90°, 105°, and 120°). Our results showed that lower knee flexion angles were generally associated with greater RSI mod values with the CMJ performed at 60° showing the greatest RSI mod ( P ≤ 0.049; effect size [ES] range = 0.19–0.63). The greatest RSI mod for the CMJ performed at 60° was caused by the proportionally lower values of the time to take‐off (ES range = 0.65–1.91) compared to the decrease observed in jump height (ES range = 0.11–0.25). The RSI mod was higher for the CMJ pref compared to the CMJ refer ( P < 0.001; ES = 0.34) due to a higher jump height ( P = 0.021; ES = 0.14) and reduced time to take‐off ( P < 0.001; ES = 0.85). These results indicate that practitioners should be careful when interpreting an individual's changes in RSI mod when the countermovement depth is not similar across the testing sessions. However, since the use of pre‐determined knee flexion angles negatively impacts the RSI mod , we encourage practitioners to use the CMJ pref but only compare the RSI mod when CMJs are performed using consistent countermovement depths.