Coactivation of ankle muscles during stance phase of gait in patients with lower limb hypertonia after acquired brain injury

ObjectiveExamine (1) coactivation between tibialis anterior (TA) and medial gastrocnemius (MG) muscles during stance phase of gait in patients with moderate-to-severe resting hypertonia after stroke or traumatic brain injury (TBI) and (2) the relationship between coactivation and stretch velocity-dependent increase in MG activity.MethodsGait and surface EMG were recorded from patients with stroke or TBI (11 each) and corresponding healthy controls (n = 11) to determine the magnitude and duration of TA–MG coactivation. The frequency and gain of positive (>0) and significant positive (p < 0.05) EMG–lengthening velocity (EMG–LV) slope in MG were related to coactivation parameters.ResultsThe magnitude of coactivation was increased on the more-affected (MA) side, whereas the duration was prolonged on the less-affected (LA) side of both stroke and TBI patients. The difference reached significance during the initial and late double support. The magnitude of coactivation positively correlated with the gain of significant positive EMG–LV slope in TBI patients.ConclusionsIncreased coactivation between TA and MG during initial and late double support is a unique feature of gait in stroke and TBI patients with muscle hypertonia.SignificanceIncreased coactivation may represent an adaptation to compensate for impaired stability during step transition after stroke and TBI.

► After stroke or traumatic brain injury, the magnitude of coactivation between tibialis anterior (TA) and medial gastrocnemius (MG) muscles is increased in the more-affected limb during initial and late double support. ► The duration of TA–MG coactivation is prolonged in the less-affected limb also during initial and late double support. ► The correlation between coactivation and stretch velocity-dependent increase in MG activity in TBI patients suggests central contribution to MG output during its lengthening in stance phase of gait.