Intrathecal baclofen bolus reduces exaggerated extensor coactivation during pre-swing and early-swing of gait after acquired brain injury.

OBJECTIVE: To characterize the concurrent activation of rectus femoris (RF) and medial gastrocnemius (MG) muscles (extensor coactivation) during gait in subjects with pronounced resting hypertonia after acquired brain injury (ABI) and examine changes after intrathecal baclofen (ITB) bolus injection.

METHODS: Magnitude and duration of extensor coactivation during different phases of gait were assessed by recording gait kinematics and activity in bilateral RF and MG muscles in 18 controls and 18 ABI subjects before and at 2, 4, and 6h after a 50-μg ITB injection.

RESULTS: Compared to controls, the magnitude of extensor coactivation was significantly increased in all phases of gait except the single support (p≤0.005), while the duration was significantly prolonged throughout (p≤0.001) in both legs of ABI subjects. After ITB bolus, only the duration of extensor coactivation significantly shortened in the more-affected leg during the late double-support and early swing (p≤0.026).

CONCLUSIONS: Extensor coactivation is bilaterally exaggerated during gait in ABI subjects. ITB bolus effectively shortens the extensor coactivation in the more-affected leg during the pre-swing and early swing phases of gait.

SIGNIFICANCE: Shortening of the prolonged extensor coactivation during gait may serve as an index of neurophysiological response to ITB bolus injection in subjects with ABI.