Glucose kinetics and exercise performance during phases of the menstrual cycle: effect of glucose ingestion

To study the effect of menstrual cycle phase and carbohydrate ingestion on glucose kinetics and exercise performance, eight healthy, moderately traine d, eumenorrheic women cycled at 70% of peak O-2 consumption for 2 h and the n performed a 4 kJ/kg body wt time trial. A control (C) and a glucose inges tion (G) trial were completed during the follicular (F) and luteal (L) phas es of the menstrual cycle. Plasma substrate concentrations were similar bef ore the commencement of exercise. Glucose rates of appearance and disappear ance were higher (P < 0.05) during the 2nd h of exercise in FC than in LC. The percent contribution of carbohydrate to total energy expenditure was gr eater in FC than in LC, and subjects performed better (13%, P < 0.05) in FC . Performance improved (19% and 26% in FG and LG compared with FC and LC, r espectively, P < 0.05) with the ingestion of glucose throughout exercise. T hese data demonstrate that substrate metabolism and exercise performance ar e influenced by the menstrual cycle phase, but ingestion of glucose minimiz es these effects.