General muscle fatigue changed joint regulations in static and dynamic balance.

This study was aimed at investigating the joint regulations and body sway after general muscle fatigue during tasks that involve both static and dynamic balance. This cross-sectional study used motion analysis to ascertain the kinematic changes in twelve healthy young individuals before and after running-induced fatigue. Six linear and nonlinear stability metrics were calculated to assess the whole body and joint-related variations. Significant instabilities were observed in the hip and specifically in the knee mechanisms and the whole body during the static condition. Velocity path length and approximate entropy for knee ( p = 0.019, p = 0.027) and hip ( p = 0.016, p = 0.042) were significantly greater after fatigue. These parameters for the whole body center of mass were also higher after fatigue ( p = 0.013, p = 0.013). General muscle fatigue did not significantly affect the ankle during static and dynamic standing ( p > 0.05). Dynamic standing did not reveal the effects of fatigue either on local joint regulations or on the whole body except for the nonlinear metrics of the proximal joints. The knee and hip were adversely affected by fatigue while the ankle strove to compensate for the fatigue-induced instability.