Effects of high frequency electrical muscle stimulation on dynamic strength of the quadricep muscle group

This study evaluated the effects of high frequency (2500 Hz) electrical muscle stimulation (EMS) on the dynamic strength of the quadricep muscle group. Twelve college-aged male volunteers, who were regularly involved in vigorous physical activity, took part in the study. The weaker leg of all subjects was pre-tested and posttested isokinetically at movement speeds of 30 and 50 degrees/second, using a Cybex II. Each subject was randomly placed in one of three groups. Group A (N=4) received EMS treatments isometrically at 65 degrees of knee flexion. Group B (N=4) received EMS treatments isometrically at both 35 and 65 degrees of knee flexion. Group C (N=4) was the control and received no stimulation. Stimulation to the weaker legs of the experimental groups consisted of 10 maximal involuntary contractions with a duration of 15 seconds per contraction interrupted by a 50-second rest interval. Each treatment session lasted approximately 15 minutes and was administered five days per week for four weeks.

A Two-Factor (stimulation, speed of movement) Analysis of Covariance, using the pre-test measurement as covariate, showed a significant difference between Groups A, B, and C (DF=2, F=12.656, P<0.001). No difference was seen for speed of movement (F=0.302), and no interaction across speed of movement and stimulation was observed (F=1.284, P>0.302). A Duncan Post-Hoc Test showed a significant difference between Groups B and C (P<0.05) but no difference between Groups A and C or Groups A and B (P>0.05). However, at P<0.10 there were significant differences among all groups.

Results of this study indicate that use of high frequency (2500 Hz) electrical muscle stimulation does increase the dynamic strength of the quadricep muscle group. Furthermore, increases in dynamic strength were greater when the subjects were stimulated at two angles of knee flexion.