Optimizing neuromuscular electrical stimulation for hand opening.

To investigate the effect of introducing an interphase interval to a biphasic pulse on force production and muscle fatigue, during stimulation of the wrist and finger extensors and to determine whether the IPI effect on force is dependent on electrode position. Electrically-induced contraction forces of the wrist and finger extensors were measured in 15 healthy subjects undergoing stimulation. These forces were assessed with interphase interval settings at 0, 100, and 200μs, with both electrodes located just distal to common extensor origin (proximal placement) or with the distal electrode placed over the extensor and abductor policies longus muscles (distal placement). The degree of discomfort related to stimulation sensation was evaluated using a numeric rating scale. Muscle fatigue was measured during proximal placement. Under both electrode locations, introduction of 100 or 200 μs interphase interval enhanced force production; yet, only the 100μs interphase interval increased force without increasing discomfort. Additionally, stimulation sensation was more comfortable with proximal placement. Introducing interphase interval significantly increased the muscle force output during a repetitive stimulation fatigue protocol. When using neuromuscular electrical stimulation to activate the wrist and finger extensors, clinicians should consider locating both stimulating electrodes proximally over the extensor surface of the forearm and apply a 100 µs interphase interval to a biphasic pulse. Future research that should establish these findings in individuals with various pathologies, especially in patients with residual hand spasticity.