Investigation of the Relationship Between Stimulus Parameters and a Human Muscle Contraction Force During Stimulation of the Gastrocnemius Muscle

The article presents the results of investigations on the influence of biphasic stimulus parameters such as duration and stimulus interphase interval (IPI) on a gastrocnemius muscle contraction force. Seven healthy volunteers participated in this experiment, and 24 different stimuli patterns were tested. Special attention was paid to the comfort level of a sensory perception while the electrostimulation was applied. During the test, an optimal stimulus pattern evoking contraction at the level over 15% maximum voluntary contraction force and preserving a good comfort perception reported by all of the participants was investigated. It was found that bursts of pulses with width 175 mu s and the IPI from 50 to 1000 mu s satisfied these criteria. Moreover, it was observed that the increase of the IPI duration generated a significantly stronger contraction force in comparison with the stimulation with the standard biphasic pulses (IPI = 0 mu s) having the same amplitude, frequency, and pulse duration. This shows that the modulation of the IPI might be a potentially useful support for the standard force-control methods and may find an application in neuromuscular electrical stimulation systems.