NEW YORK (Reuters Health) – Women have significantly lower electrical sensory and supramotor thresholds than men, according to recent findings published in the April issue of the Annals of Neurology.

“Surface electrical stimulation of skeletal muscle has several clinical applications, including restoration/improvement of muscle function (e.g., in neurorehabilitation) and pain management,” Dr. Nicola A. Maffiuletti, of Schulthess Clinic, Zurich, Switzerland, and colleagues note. “Men are generally considered to be more electrically excitable than women, because the former have proportionately more muscle mass and less adipose mass,” they note. “However, to our knowledge, few or no data exist regarding sex differences in electrical stimulation current levels.”

To investigate, the researchers examined sex-related differences in electrical sensory (current perception), motor (minimal knee extension torque production), and supramotor (10% of the maximal voluntary knee extension torque) thresholds. They also assessed perceived pain during surface electrical stimulation of the quadriceps femoris muscle.

Included in the study were 40 healthy volunteers (20 men and 20 women) free of known orthopedic, neuromuscular, or cardiovascular problems.

The authors report that sensory threshold was lower in women than in men (-43%, p < 0.001), as was supramotor threshold (-17%, p < 0.01). No significant differences between the sexes were observed for motor threshold.

The team found that the lowest sensory thresholds were found in subjects with the largest skinfold thickness and vice versa. The Visual Analogue Scale pain score at motor threshold was significantly greater in women than in men (+112%, p < 0.01).

“Our findings may help clinicians and practitioners better understand the sex-specific response to percutaneous electrical stimulation (e.g., women require lower current doses and present greater pain) and to design more rational stimulation strategies,” Dr. Maffiuletti said in an email interview with Reuters Health. “In agreement with recent skin biopsy and cadaveric studies, our findings favor a neurophysiological rather than a psychological or sociological explanation for more pronounced pain perception in female individuals.”

They are currently examining obese, orthopedic and neuromuscular patients to verify if these findings can be generalized to unhealthy populations, the author said.

Ann Neurol 2008;63:507-512.

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