A pilot study on the effect of oral contraceptives on electromyography and mechanomyography during isometric muscle actions.

The purpose of this pilot study was to determine the influence of oral contraceptives (OC) on electromyography (EMG) and mechanomyography (MMG) during isometric (ISO) muscle actions of the rectus femoris. Two groups of women (Mean +/- SEM, 24 +/- 1 yrs, 1.68 +/- 0.02 m, 70.97 +/- 4.81 kg) were recruited and tested five times throughout one complete menstrual cycle. The first group (n=7) were not taking hormonal treatment (NOC) and the OC group (n=6) had been taking exogenous hormones for at least six months prior. Each participant performed maximal ISO muscle actions (MVC) of the leg extensors on a Cybex II isokinetic dynamometer followed by randomly assigned sub-maximal ISO muscle actions. Bipolar surface EMG electrodes were placed over the rectus femoris with a piezoelectric MMG recording device placed between the two electrodes. Three separate three way (group x day x %MVC) mixed factorial repeated measures ANOVAs were used to determine differences in torque, EMG and MMG between NOC and OC subjects. There were no significant three-way interactions involving group for normalized torque, EMG or MMG. These results indicated that OC does not have an effect on torque, EMG or MMG during ISO muscle actions of the rectus femoris.