Joint-level determinants of the dynamic strength index: implications for testing and monitoring.

The aims of this study were to determine the associations and differences between the traditional dynamic strength index (DSI GRF , calculated from ground reaction force [GRF] data) and joint-level dynamic strength indices (DSI NJM , calculated from net joint moment [NJM] data). Eight female NCAA Division I lacrosse players performed three maximal effort isometric mid-thigh pulls (IMTP) and countermovement jumps (CMJ). GRF and motion capture data were recorded and used to calculate hip, knee, and ankle NJM. The ratio between peak forces during the IMTP and CMJ tests was used to calculate the DSI GRF and the ratio of peak NJM was used to calculate ankle, knee, and hip DSI NJM . Associations and differences between DSI GRF and DSI NJM were examined with Pearson's correlation coefficients, paired t -tests and Hedge's g effect sizes. The results showed that only the hip DSI NJM was correlated with DSI GRF (hip: p  = 0.037; r = 0.738). In addition, athletes exhibited significantly greater DSI NJM than DSI GRF . Although these results suggest DSI GRF are associated with hip DSI NJM , the fact that joint-level DSI NJM were generally greater than DSI GRF suggests the ratio between peak NJM during the CMJ and IMTP may not provide intuitive or useful data for strength and conditioning coaches or sport scientists.