The effects of medial gastrocnemius muscle fatigue on regional modulation of the ankle plantarflexors during standing external perturbations

Regional modulation of electromyography (EMG) with perturbation direction within each plantarflexor (evidenced by the EMG barycenter shift) was lost in fatigued medial gastrocnemius (MG) but was maintained in unfatigued synergists. Regional modulation of EMG following directional perturbations was associated with center of pressure (COP) displacement, reinforcing that the shift in EMG barycenter was serving to oppose the perturbation. Responses to directional perturbations helped counteract low-frequency fatigue of MG by decreasing postural sway and increasing EMG amplitude in both MG and lateral gastrocnemius (LG).