Lower-extremity joint quasi-stiffness in graded running

Lower extremity joints illustrate torsional spring-like behaviour during running. While the influence of running speed and different strike patterns on joint quasi-stiffness have been investigated, the changes associated with graded running are not known. Ankle and knee joint stiffness of twelve rear foot strike runners were calculated at 3.33 m.s-1 and five different gradients. Results illustrated that the lower energy absorption requirements of uphill running (UR) were accomplished by increasing knee joint quasi-stiffness, while the higher energy absorption requirements of downhill running (DR) were accomplished by reducing ankle joint quasi-stiffness. Foot strike pattern modifications during graded running may explain these observations.