Sustained voluntary muscle contractions can lead to fatigue, which diminishes the muscle’s ability to absorb energy and produce force at a desired level. Prolonged fatigue can lead to a decline in human performance and increase the muscle’s susceptibility to injury. In this study, we investigated how localized muscle fatigue affected spatial EMG patterns during locomotion. We recorded high-density electromyography (EMG) from the medial gastrocnemius of 11 healthy subjects while they walked (1.2 m/s) and ran (3.0 m/s) on a treadmill before and after performing a task that locally fatigued their ankle plantarflexor muscles. We applied multivariate signal cleaning methods to remove motion artifacts from the recorded signals. From these data, we computed the peak EMG amplitude, spatial entropy, peak EMG barycenter, and mean power frequency content during walking and running before and after subjects fatigued. We also calculated sagittal plane lower limb joint kinematics and kinetics in each condition. We found that peak EMG activity significantly decreased during walking and running after the fatigue task, and the location of the peak EMG barycenter had shifted proximally compared to its prefatigue location. We also observed an increase in the EMG mean power frequency during locomotion postfatigue. Despite the changes in spatial EMG activation, lower limb biomechanics were similar before and after fatigue. These results suggest that motor unit recruitment was altered to sustain force production and forward propulsion. This may be a protective mechanism to more broadly distribute muscle loads and avoid myotendinous injury.

NEW & NOTEWORTHY This research investigates the effects of muscle fatigue on spatial myoelectric patterns in the lower limb during locomotion. Both spatial and frequency aspects of neuromuscular recruitment in the medial gastrocnemius change in response to fatigue, resulting in altered myoelectric patterns during walking and running. These data may help us better understand the adaptations that occur in lower limb muscles to avoid overuse injuries caused by fatigue.