Lower limb coordination and stiffness during landing from volleyball block jumps

The aim of the study was to investigate lower limb coordination and stiffness in five male and five female university volleyball players performing block jump landings. Coordination was assessed using angle-angle plots of the hip-knee, knee-ankle and hip-ankle joint couplings and discrete relative phase (DRP) of right-left joint couplings (i.e., left knee coupled with right knee). Leg stiffness was calculated as the ratio of the change in vertical ground reaction force (GRF) to the change in vertical displacement of the centre of gravity between ground contact and maximum vertical GRF. Knee stiffness was calculated as the ratio of the change in knee joint moment to the change in knee flexion angular displacement between ground contact and maximum knee joint moment. Comparison of the DRP angles between left and right legs indicated reduced symmetry between the left and right legs in females compared with males, which may indicate greater likelihood of ligament strain in females compared with males. Furthermore, females exhibited reduced stability in the coordination between the left and right knee joints than males. Males exhibited significantly greater absolute and normalised leg stiffness and significantly greater absolute and normalised knee joint stiffness during landing compared with females. In conjunction with the coordination data, this may indicate reduced dynamic stability of the leg in females compared with males, which may contribute to the greater incidence of anterior cruciate ligament (ACL) injury in females compared with males.