A brief interphase interval interposed within biphasic pulses enhances the contraction force of the quadriceps femoris muscle

There is still unsettled controversy regarding the optimal neuromuscular electrical stimulation (NMES) parameters that will induce the strongest contractions with minimal discomfort. The purpose of this study was to determine whether the introduction of an interphase interval (IPI) interposed within the two phases of biphasic pulses will affect sensory and motor thresholds, the force of the electrically induced contractions (EIC), and the degree of discomfort associated with these contractions. Within subjects, repeated measures design was employed with 29 healthy young volunteers. Sensory and motor thresholds and the force of the EIC were determined with biphasic pulses. Five different settings were tested in random order with IPIs ranging between 0 and 250 mu sec. Introducing IPIs during stimulation with biphasic pulses enhanced force production, with the increase related to the duration of the IPI. The sensory and motor thresholds, as well as the degree of discomfort associated with the induced contractions, were not affected by the IPIs. Biphasic pulses that incorporate IPIs may increase the effectiveness of NMES in terms of force production.