A PILOT STUDY ON THE EFFECT OF MENSTRUAL CYCLE ON TORQUE, ELECTROMYOGRAPHY, AND MECHANOMYOGRAPHY

Abstract

The purpose of this pilot investigation was to determine the effect of the menstrual cycle on torque production and amplitudes of electromyography (EMG) and mechanomyography (MMG) during isometric muscle actions of the rectus femoris. Two groups of healthy, active women (24.4 ± 4.6 yrs, 71.45 ± 19.31 kg, 1.67 ± .07 m) were recruited and tested five times through one complete menstrual cycle. The first group (n = 6) were not taking any form of hormonal treatment (NOC) and all had normal menstrual cycles lasting between 26 and 32 days. The second group (n = 5) had been taking oral contraceptive (OC) for at least 6 months. Each participant performed maximal isometric muscle actions (MVC) of the leg extensors on a Cybex II isokinetic dynamometer at 45o of leg flexion followed by randomly assigned sub-maximal isometric muscle actions at 25, 50 and 75% of MVC. The OC group tested on days 1, 5, 10, 15, and 20 of their menstrual cycle. The NOC group tested on days 1, 5, 10, ovulation, and 5 days post ovulation. Ovulation was predicted using basal body temperature and ovulation kits. Bipolar surface EMG electrodes were placed mid-thigh over the rectus femoris with a piezoelectric MMG recording device placed between the two electrodes. Three separate three-way (group × day × % MVC) mixed factorial repeated measures ANOVAs were used to determine differences in EMG amplitude (μV), MMG amplitude (mV), and torque (Nm) across the menstrual cycle for both the NOC and OC groups. There were no significant three-way or two-way interactions involving “group” for EMG amplitude, MMG amplitude, or torque. Therefore, the subjects exhibited the same pattern of responses across the menstrual cycle and at the various levels of MVC.