Control of thumb movements: EMG analysis of the thumb and its application to functional electrical stimulation for a paralyzed hand.

This paper describes the control of thumb movements by functional electrical stimulation (FES). In order to determine stimulation data of thumb muscles, activities of nine thumb muscles and the palmaris longus were analyzed in normal subjects by averaging their EMGs. In this analysis, it was found that well coordinated contractions of these thumb muscles were required for finer movements and precise positioning of the thumb. Based upon this analysis, several standard stimulation data for the thumb muscles were programmed and stored into a computer-controlled FES system. Input of the threshold and maximum stimulating voltages for individual thumb muscles of normal subjects to the system enabled automatic creation of stimulation data for each subject. The thumb movements of the normal subjects induced by these data were very smooth and their trajectories were reproducible. In addition, precise thumb positioning and joint stability were easily obtained. These standard stimulation data for the thumb muscles were also applied to FES control of a C4 quadriplegic. The controllability of the thumb movements was improved and the reliability of hand tasks achieved by FES was increased.