Background: Foot drop is a common gait impairment after stroke. Functional electrical stimulation (FES) of the ankle dorsiflexor muscles during the swing phase of gait can help correct foot drop. Compared with constant-frequency trains (CFTs), which typically are used during FES, novel stimulation patterns called variable-frequency trains (VFTs) have been shown to enhance isometric and nonisometric muscle performance. However, VFTs have never been used for FES during gait.
Objective: The purpose of this study was to compare knee and ankle kinematics during the swing phase of gait when FES was delivered to the ankle dorsiflexor muscles using VFTs versus CFTs.
Design: A repeated-measures design was used in this study.
Participants: Thirteen individuals with hemiparesis following stroke (9 men, 4 women; age=46-72 years) participated in the study.
Methods: Participants completed 20- to 40-second bouts of walking at their self-selected walking speeds. Three walking conditions were compared: walking without FES, walking with dorsiflexor muscle FES using CFTs, and walking with dorsiflexor FES using VFTs.
Results: Functional electrical stimulation using both CFTs and VFTs improved ankle dorsiflexion angles during the swing phase of gait compared with walking without FES (X+/-SE=-2.9 degrees +/- 1.2 degrees). Greater ankle dorsiflexion in the swing phase was generated during walking with FES using VFTs (X+/-SE=2.1 degrees +/- 1.5 degrees) versus CFTs (X+/-SE=0.3+/-1.3 degrees). Surprisingly, dorsiflexor FES resulted in reduced knee flexion during the swing phase and reduced ankle plantar flexion at toe-off.
Conclusions: The findings suggest that novel FES systems capable of delivering VFTs during gait can produce enhanced correction of foot drop compared with traditional FES systems that deliver CFTs. The results also suggest that the timing of delivery of FES during gait is critical and merits further investigation.