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

O₂ uptake \((\dot{V}O_{2})\) 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 \(\dot{V}O_{2}\) response to moderate-intensity exercise. Seven healthy women (age 21 ± 2 years; mean ± SD) performed six transitions from 20 W to moderate-intensity exercise (∼ 90 % \(\hat{\theta}_{{{\rm L}}}\)) during the F and L phase. \(\dot{V}O_{2}\) was measured breath-by-breath and deoxyhemoglobin/myoglobin (Δ HHb) was determined by near infrared spectroscopy. Progesterone and estrogen were significantly (P < 0.05) elevated during the L compared to F phase. \(\dot{V}O_{2}\) kinetics \((\tau \dot{V}O_{2})\) 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 Δ HHb response (F, TD 11 ± 2 s, τ 11 ± 3 s; L, TD 12 ± 2 s, τ 12 ± 11 s; τHHb 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, \(\dot{V}O_{2}\) 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 Δ HHb in combination with unchanged \(\dot{V}O_{2}\) suggests that there were no differences in the adaptation of local muscle O₂ delivery.