The effects of menstrual cycle on electromyography and mechanomyography during isotonic muscle actions and fatigue
The purpose of this investigation was to determine whether there are changes in electromyography (EMG) and mechanomyography (MMG) between woman using oral contraceptives (OC) and non-oral contraceptive (NOC) subjects during concentric (CON) and eccentric (ECC) muscle actions and during fatigue over one menstrual cycle phase. Eighteen healthy, physically active women (Mean ± SEM, 24 ± 1 yrs, 1.64 ± 0.69 m, 60.5 ± 1.6 kg) were recruited and tested six times throughout one complete menstrual cycle. The NOC group ( n = 9) was not taking any form of hormonal treatment and all had normal menstrual cycles lasting between 26 and 32 days. The second group (n = 9) had been taking OC for at least 6 months. Each participant performed one maximal isotonic strength (1-RM) test of the leg extensors. For each of the six testing sessions, each participant performed randomly assigned 3-s submaximal isotonic muscle actions at 20, 40, 60 and 80% of 1-RM and a fatigue protocol at 50% of 1-RM. Bipolar surface EMG electrodes were placed mid-thigh over the rectus femoris with a piezoelectric MMG recording device placed between the two electrodes. Four separate three-way (group by day by percent of 1-RM) mixed factorial repeated measures ANOVAs were used to determine differences in normalized isotonic CON EMG, ECC EMG, CON MMG, and ECC MMG across the menstrual cycle for both the NOC and OC groups. Four two-way (group by day) mixed factorial repeated measures ANOVAs were used to determine differences in normalized slope values obtained during the fatigue protocol for CON EMG, ECC EMG, CON MMG and ECC MMG. There were no significant three-way interactions involving group for isotonic CON EMG, ECC EMG, CON MMG or ECC MMG across the menstrual cycle. Furthermore, there were no significant two-way interactions involving group for CON EMG, ECC EMG, CON MMG or ECC MMG across the menstrual cycle. Therefore, there are no differences in electrical or mechanical activity of the rectus femoris between NOC and OC subjects.