Torque responses in human quadriceps to burst-modulated alternating current at 3 carrier frequencies.

Study Design Independent group design, 1 group per carrier frequency, with subjects stratified by gender and systematically assigned to groups. Objective To determine the effect of the frequency of burst-modulated alternating current (AC) on the electrically induced torque (EIT) response of the quadriceps femoris muscle. Background Many studies have examined the influence of current amplitude and burst modulation on the EIT response. However, research is limited on the effects of carrier frequency on the EIT response of the quadriceps femoris. Methods and Measures Twenty-three healthy subjects (mean age ± SD, 22.7 ± 1.7 years) volunteered for the study and were systematically assigned to 1 of 3 groups: group 1 (2500-Hz AC), group 2 (3750-Hz AC), and group 3 (5000-Hz AC). For normalization purposes, maximal voluntary isometric contraction (MVIC) force was assessed with a load cell prior to the application of 5 minutes of neuromuscular electrical stimulation (NMES). The EIT and current amplitude were record...