Efficacy of two forms of electrical stimulation in increasing quadriceps strength: a randomized controlled trial

Objective: To investigate whether electrical stimulation is effective in improving quadriceps strength in healthy subjects and to compare interferential and low-frequency current in terms of the effects on quadriceps strength and perceived discomfort. Design: Randomized, controlled study. Setting: Physical Medicine and Rehabilitation Department in a university hospital. Subjects: Thirty medical faculty students, divided into three groups, participated in the study. Interventions: Group A received electrical stimulation with bipolar interferential current while group B received electrical stimulation with low-frequency current (symmetrical biphasic). Group C served as the control group. Electrical stimulation was given for 15 minutes, five days a week for three weeks, at a maximally tolerated intensity with the knee fully extended in the sitting position. Main outcome measures: Before and after the study, quadriceps strength was measured with a Cybex dynamometer isokinetically at the angular velocities of 60degrees/s and 120degrees/s. The perceived discomfort experienced with each type of electrical stimulation was quantified by the use of a visual analogue scale (VAS). Results: Statistically significant increase in isokinetic strength was observed after training in group A and group B. Increase in strength did not differ between the stimulation groups. No significant change in strength occurred in group C. Perceived discomfort by the stimulation groups was not significantly different. Conclusion: Both interferential and low-frequency currents can be used in strength training with the parameters used in this study.