Differences in electrical stimulation thresholds between men and women.

Abstract

Surface electrical stimulation (ES) of skeletal muscle is used in a variety of clinical settings in healthy and unhealthy subjects of both sexes. Although women generally present larger amounts of subcutaneous adipose tissue than men, which could limit current flow to the stimulated muscle, sex-related differences in ES current levels have not been clearly demonstrated to date. We report data from healthy men and women. Sensory (current perception), motor (minimal knee extension torque production), and supramotor thresholds (10% of the maximal voluntary knee extension torque) and perceived pain during surface ES of the quadriceps femoris muscle were investigated in 40 healthy volunteers (20 men, 20 women). Sensory threshold was lower in women than in men (-43%; p < 0.001). Similarly, female muscles required lower current amplitudes to attain the supramotor threshold (-17%; p < 0.01). The Visual Analogue Scale pain score was significantly greater in women than in men at motor threshold (+112%; p < 0.01) but not at supramotor threshold (+36%; p > 0.05). Collectively, our data demonstrate higher sensory and supramotor excitability to surface ES in female subjects and provide further evidence for a neurophysiological explanation for more pronounced pain perception in women. These observations may help clinicians to better understand the sex-specific response to ES and to design more rational stimulation treatments with the ultimate goal of optimizing patient care and safety.