SUBSTRATE RESPONSES TO SUBMAXIMAL EXERCISE IN THE MIDFOLLICULAR AND MIDLUTEAL PHASES OF THE MENSTRUAL-CYCLE

This study examined substrate metabolism responses of eumenorrheic wom en to different intensities of submaximal exercise at the midfollicula r (MF) and the midluteal (ML) phases of the menstrual cycle. Nine wome n performed a 30-min treadmill run in which the exercise intensity was made more difficult every 10 min (35%, 60%, and 75%). Carbohydrate (C HO) utilization and oxidation rates for the 35% and 60% intensities du ring the ML session were significantly lower than during the comparabl e intensities in the MF. Conversely, lipid utilization and oxidation w ere significantly greater during the 35% and 60% ML session than in th e MF session. At 75%, however, the ML and MF CHO-lipid utilization and oxidation rates were not significantly different from one another. Th us, the phase of the menstrual cycle in eumenorrheic women does influe nce metabolic substrate usage during low- to moderate-intensity submax imal exercise, probably due to changes in the endogenous levels of the female sex hormones.