The Impact of Localized Muscle Fatigue on Multi-Joint Biomechanical Strategies During Stair Ascent

The objective of this study was to investigate the impact of localized muscle fatigue (LMF) in the hip, knee, and ankle muscle groups on stair ascent biomechanics, with a focus on identifying compensatory mechanisms following fatigue. Twenty-five participants were fatigued using an isokinetic dynamometer to induce unilateral muscle fatigue in the hip extension, knee extension, and ankle plantarflexion muscles through repetitive isokinetic contractions. We collected stair ascent data before fatigue and after three different fatigue protocols, simultaneously collecting kinematic, kinetic, and electromyographic data. The effects of different muscle fatigue conditions on stair ascent performance were assessed using one-way repeated-measures ANOVA. Key findings revealed that hip fatigue narrowed step width and increased ankle dorsiflexion. Knee fatigue reduced knee extensor moments on the fatigued side and increased hip extension moments bilaterally. Ankle fatigue decreased plantar flexion and increased hip extension moments. Electromyographic data confirmed corresponding shifts in muscle activation. Collectively, the results suggest that localized lower-limb fatigue may alter stair ascent biomechanics in a joint-specific manner. The observed changes in joint moments and muscle activation may reflect a bidirectional pattern of inter-joint compensation, with proximal-to-distal or distal-to-proximal adjustments depending on the fatigued joint. These findings suggest that mechanical and neuromuscular demands may be redistributed across lower-limb joints under acute fatigue conditions; however, given that this study was conducted in healthy young males, the relevance of these findings to stair-related instability or fall risk in more vulnerable populations should be examined in future studies.