The effects of medial gastrocnemius muscle fatigue on regional modulation of the ankle plantarflexors during standing external perturbations
Abstract
The ankle plantarflexor muscles (soleus, medial, and lateral gastrocnemius) exhibit direction-specific regional modulation of muscle activity during external perturbations. This study sought to investigate the effect of medial gastrocnemius muscle fatigue on plantarflexor muscle activation patterns. Unipedal balance was tested during external perturbations that challenged standing balance in different directions before and after low-frequency fatigue was induced to the medial gastrocnemius via electrical stimulation. High-density surface electromyography was used to determine the amplitude and barycenter of muscle activation. It was hypothesized that the central nervous system would compensate for a loss of force-generating capacity in the medial gastrocnemius by modulating the activity of the soleus and lateral gastrocnemius to maintain balance. The soleus experienced an increase in muscle-activation amplitude and a proximal barycenter shift when the medial gastrocnemius was fatigued. However, the direction-specific regional modulation of plantarflexor muscle activity was not significantly affected by medial gastrocnemius fatigue.