[Effects of frequency on muscular force induced by electric stimulation]

The aim of this work is to determine the effect of low frequency current (L) versus medium frequency current (M) in order to generate a different force level on soleus and gastrocnemius muscles. The experiment was conducted on 10 healthy, male volunteer subjects aged from 19 to 21 who provided informed consent to participate in the experiment. None of the subjects had experienced electrostimulation (ES) procedures before. The subjects were seated with vertical legs and horizontal thighs. Isometric force of the gastrocnemius and soleus muscles was measured using a strain gage dynamometer (100 daN). The transducer was adjusted on the knee, along the vertical axis of the leg. For the conditions of ES, a bi-phasic, symmetrical square wave signal was applied at each of five low frequencies: 20, 40, 60, 80 and 100 Hz and at each of six medium frequencies (2222 Hz) modulated or not, to yield 20, 40, 60, 80, 100 bursts of pulses. Maximum voluntary contraction (MVC) was also recorded. The phase duration was constant throughout 180 microseconds. The current level was set individually for each subject at the maximum that could be tolerated and applied during 10 s. Each contractile condition was randomly chosen. The forces produced by the different regimen of ES used are significantly different (P < 0.001). For each type of stimulation we got tetanic contractions. After an initial ramp, a nearly flat curve corresponding to tetanus was reached. For a 60 hz low frequency current, the force production reached 76% of MVC for a mean intensity of 58 mA, corresponding to a charge of 1253 microC.(ABSTRACT TRUNCATED AT 250 WORDS)