Effect of leg muscle fatigue on gait pattern & human balance

Abstract

Leg muscle fatigue could induce impaired control of human balance, walking, and a high risk of falls. This study aimed to investigate the effect of leg muscle fatigue on human balance under both static and dynamic conditions by combining different analysis approaches. Three tasks were assessed, including quite standing, unobstructed walking, and obstructed walking with obstacle crossing at two different obstacle heights. Twenty young healthy subjects participated in this experiment, and they performed quiet standing, unobstructed walking, and obstructed walking over an obstacle with two different heights before and immediately after a leg muscle fatigue protocol. Center of Pressure (COP) trajectory during quiet standing was collected by a balance board to assess the static balance. Gait parameters derived from wearable inertial sensors data were evaluated during unobstructed walking trials and obstructed walking trials. Also, foot clearance distances were measured by an optical motion capture system during obstacle crossing. Squatting was chosen as the fatigue task to induce leg muscle fatigue. COP based body sway measures and unobstructed walking trials were analyzed by paired samples t-test to compare before fatigue and after fatigue trials. Two-way Analysis of Variance (ANOVA) repeated measures was used to assess the effects of fatigue state and obstacle height during obstructed walking. Experimental results showed that all of COP based body sway measures (planar deviation, range in anteroposterior (AP) and mediolateral (ML) direction, mean distance, mean distance in ML and AP direction, path sway, RMS distance, RMS distance in ML and AP, mean velocity, and mean velocity in ML and AP direction and phase planar parameter) showed a statistically significant increase after fatigue, indicating higher body sway and impaired static balance. During Unobstructed walking trials, gait speed and stride length were affected after fatigue showing a significant decrease. When performing obstacle crossing trials, no significant interaction between fatigue state and obstacle height was found. However, after fatigue, gait speed and relative stance were affected, showing a decreasing trend. Obstacle height also affected stride length showing an increasing trend, while the number of strides decreased when the obstacle was higher. For foot clearances, participants tended to place the leading foot after crossing the obstacle closer due to fatigue but left a greater distance when the obstacle was higher. When crossing an obstacle, the trailing foot distance was affected by fatigue state, increasing when the obstacle was higher. All of the other distances remained unchanged. These results show that fatigue affects static balance by increasing body sway with a more prominent movement in the anteroposterior direction. However, the relative increase of path sway larger than the MDIST has been interpreted as an effective postural control regulation. Therefore, even after fatigue, participants can compensate for motor and/or sensory deficiencies. From the dynamic balance perspective, participants adopted different strategies for gait pattern according to different scenarios (unobstructed and obstructed path), which furthermore was reflected in the foot clearances when performing obstructed walking trials. In conclusion, kinematic variables are affected by fatigue

however, the whole-body balance was maintained due to young healthy adults' ability to adapt their gait depending on the environment's complexity to preserve balance and guarantee safety. These findings could not only help us to understand better the fatigue effect on human balance and gait performance but also serve as a foundation for future research in human balance and assess gait adaptability programs that help improve obstacle avoidance and address fall prevention.