Evaluation of a Drop Foot Stimulator FES Intensity Envelope Matched to Tibialis Anterior Muscle Activity during Walking

A “natural” stimulation strategy is proposed based on muscle activation patterns observed in healthy gait. This stimulation approach was tested on a 52-year old hemiplegic drop foot subject who is ten years poststroke using a computer-based FES control system. Dorsiflexion angle range was recorded for the subject while walking without orthosis, walking with the “natural” stimulation approach and walking with the conventional trapezoidal stimulation approach. The “natural” approach was found to result in a 76 % increase in dorsiflexion range for the subject, while using only on average 53 % of the stimulation used by the conventional approach. The improved performance of the “natural” stimulation approach is attributed in this case to the subject’s calf spasticity, which was rated on the modified Ashworth scale as 3-4, indicating moderate to severe spasticity. The “natural” stimulation envelope is thought to result in a less severe spastic reaction of the calf muscles during dorsiflexion than the conventional trapezoidal approach, enabling a greater dorsiflexion range as a result.