The reliability of novel, temporal-based dynamic strength index metrics

Abstract

ABSTRACT The purpose of this study was: i) to determine the reliability of alternate forms of the dynamic strength index (DSI) calculated over time-specific intervals that represent decisive actions in sport and ii) to assess the association between the original form of the DSI (DSI trad ) and its variants. Twenty-three resistance-trained males (BM = 80.4 ± 10.18 kg; age = 26.3 ± 10.2 y; 1-RM squat kg/kg/BM = 1.61 ± 0.37) performed trials of the countermovement jump (CMJ) and isometric squat. Several variations of the DSI were calculated by dividing the mean force in the CMJ by the mean force in the isometric squat calculated over the following epochs: 100 ms (DSI 100 ), 150 ms (DSI 150 ) and CMJ propulsive phase duration (DSI prop ). In the fourth method, mean force across the CMJ propulsive phase duration was divided by mean force in the isometric squat between initiation and peak force (DSI peak ). All alternate DSI measures achieved acceptable absolute reliability (CV < 10%), however they did not achieve at least a moderate relative reliability. DSI prop (R2 = 0.41), DSI 100 (R2 = 0.03) and DSI 150 (R2 = 0.14) demonstrated limited commonality with DSI trad . The alternate forms of DSI can cautiously be considered in strength assessment systems.