Walking while resisting a perturbation: Effects on ankle dorsiflexor activation during swing and potential for rehabilitation

Motor control studies have shown that when walking is performed while resisting a perturbation applied to the lower limb, the muscle activation pattern can be temporarily modified. The objective of the present study is to validate if such an approach, targeting the ankle, could specifically promote an increased activation of the ankle dorsiflexor muscles that are of key importance for the rehabilitation of foot drop. Methods: 12 adults, with no gait deficit, walked on a treadmill for three periods of 5 min: before, during and after exposure to a torque perturbation applied by a robotized ankle-foot orthosis that tended to plantarflex the ankle during the swing phase. Spatiotemporal gait parameters, ankle and knee kinematics, and the electromyographic activity of five lower limb muscle groups were recorded. Results: The perturbation initially caused a deviation of the ankle towards plantarflexion. This movement error was rapidly reduced and associated with a large increase (78.2%; p <0.001) in tibialis anterior (ankle dorsiflexor; TA) activation, specifically in the stance-to-swing burst. This increase carried over to post-perturbation walking, gradually disappearing over several strides. Interestingly, these aftereffects led to an increase in peak ankle dorsiflexion of approximately 7 degrees during the swing Phase. Conclusions: Walking while resisting a torque perturbation applied at the ankle during swing promotes an increase in TA muscle activation that carries over after perturbation removal, leading to an increased ankle dorsiflexion. Training based on this approach may have the potential of improving the gait of persons with foot drop. (C) 2011 Elsevier B.V.. All rights reserved.