In the last two decades, functional electrical stimulation (FES) has been investigated as a means for replacing lost function of limbs. resulting from paralysis. Improvement in the gait of hemiplegic patients when gradually varying stimulation sequences were employed to control footdrop during the swing-phase of gait, led to the work presented in this thesis.

The material described below is original to the field of FES.

Two potential controllers of stimulus intensity and hence ankle joint position on the affected side have been explored. These are:​ the electromyographic (EMG) activity of the corresponding dorsiflexor and plantarflexor muscles on the contralateral side;​ and ankle-joint angle variations obtained from the contralateral side. The variance ratio, a statistical descriptor for repeatability, has been invoked to quantify the efficacy of EMG and joint position control. Practical time-constants of averaging have been determined for the processing of control and evoked EMG signals to be used in an FES-based orthosis incorporating feedback. Experiments have indicated that EMG, when used to modulate stimulus strength to effect control of ankle-joint position, is as efficacious as joint-angle-variation control. These experiments revealed that joint-position information is contained in the EMG records obtained from the prime movers during specific movements of the ankle joint.

This thesis describes an initial attempt to control the affected ankle-joint position of hemiplegics during locomotion. Corresponding signals available from the contralateral side were used to modulate stimulus intensity on the affected side. A computer-controlled interactive program has been used to impose a delay proportional to the period of stepping between recording of the control signals and activation of the stimulators. Preliminary results obtained from a normal and a hemiplegic subject are presented, and their relevance to future thrusts in the field of FES are discussed.