O2 uptake and muscle deoxygenation kinetics during the transition to moderate-intensity exercise in different phases of the menstrual cycle in young adult females.

O(2) uptake (VO2) kinetics were examined during the follicular (F) and luteal (L) phases of the menstrual cycle to determine if there was an effect of altered sex hormones on the (VO2) response to moderate-intensity exercise. Seven healthy women (age 21 +/- 2 years; mean +/- SD) performed six transitions from 20 W to moderate-intensity exercise (approximately 90% theta L) during the F and L phase. VO2 was measured breath-by-breath and deoxyhemoglobin/myoglobin (Delta HHb) was determined by near infrared spectroscopy. Progesterone and estrogen were significantly (P < 0.05) elevated during the L compared to F phase. VO2 kinetics (tau VO2) were not different in the two phases of the menstrual cycle (F, 22 +/- 5 s; L, 22 +/- 6 s; 95% confidence intervals +/-4 s) nor was the time course of the Delta HHb response (F, TD 11 +/- 2 s, tau 11 +/- 3 s; L, TD 12 +/- 2 s, tau 12 +/- 11 s; tau HHb 95% confidence intervals +/-3 s). Respiratory exchange ratio (RER) was not different between phases for baseline or steady-state exercise and the blood lactate response to exercise was not different. In conclusion, VO2 kinetics at the onset of moderate-intensity exercise are not affected by the phase of the menstrual cycle in young females suggesting either no change in, or no effect of metabolic activation on the on-transient kinetics of moderate-intensity exercise. Additionally, the similar adaptation of Delta HHb in combination with unchanged VO2 suggests that there were no differences in the adaptation of local muscle O(2) delivery.