Contractile characteristics on electrical stimulation of muscle with multiple motor points. An in vivo study in rabbits.

The purpose of this study was to investigate the significance of motor points in muscle and to determine their role in functional electrical stimulation. The long head of the triceps in adult female rabbits was used as the muscle model to study the contractile response to electrical stimulation of 1 motor point as opposed to simultaneous stimulation of multiple motor points in the muscle belly. The contractile response was studied with gradually increasing voltage amplitude and with or without added loads. Simultaneous stimulation of multiple motor points gave a consistently greater range of elbow extension when compared with stimulation of individual motor points. At low-voltage values, simultaneous stimulation of multiple motor points gave excursions obtainable only with high voltages on a single motor point. This pattern was observed with and without loads. These findings indicate that for optimal control of muscle contraction in functional electrical stimulation, electrodes may need to be inserted into multiple motor points for a given muscle. Stimulation for maximal muscle function then may be possible in the optimal low-voltage range without relying on spillover effect of high voltages. Nerve, muscle, and electrode damage also may be avoided.