Effects of Combined Fatigue and Asymmetric Loading on Knee Kinematics During Walking Gait

Abstract

Abstract. Fatigue and asymmetrical loading can alter gait mechanics, yet their combined effects on knee kinematics during walking remain under-investigated. This single-subject pilot examined how squat-induced fatigue interacts with one-hand load carriage to influence knee flexion, abduction, and internal rotation. Three-dimensional kinematics were collected using a Vicon system, and clinical knee angles were computed with a modified Grood–Suntay joint coordinate system (JCS). The protocol included normal walking (NW), asymmetrical load carriage (farmer's carry, left hand), and postfatigue trials following 25, 50, 75, and 100 body-weight squats. Fatigue was associated with increased flexion variability and greater flexion at heel strike and early stance. Abduction and internal rotation waveforms remained generally consistent across fatigue levels; however, frontal-plane variability was greatest during asymmetrical loading prior to fatigue. Stride-length variability increased markedly in the 100-squat condition, suggesting a faster but less stable gait strategy under maximal fatigue. Together, the results demonstrate joint-specific and phase-dependent adaptations to fatigue and asymmetrical loading. Increased variability, particularly in flexion, likely reflects compensatory mechanisms that redistribute mechanical demand across the lower limb. While preliminary, these findings motivate larger, bilateral studies incorporating kinetics and electromyography (EMG) to refine rehabilitation and ergonomic recommendations for loaded walking.