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 (similar to 90 % (theta) over cap (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. tau 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 D HHb response ( F, TD 11 +/- 2 s, s 11 +/- 3 s; L, TD 12 +/- 2 s, s 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 D HHb in combination with unchanged tau VO2 suggests that there were no differences in the adaptation of local muscle O-2 delivery.