Menstrual cycle effects on cardiovascular drift and maximal oxygen uptake during exercise heat stress.

ABSTRACT

AIM: Compared to other modulators of physiological strain associated with exercise heat stress, hyperthermia results in the greatest magnitude of cardiovascular (CV) drift and associated decrements in maximal oxygen uptake ([Formula see text]). PURPOSE: To determine if elevated core temperature in the luteal phase (LP) of the menstrual cycle results in greater CV drift and reductions in [Formula see text] versus the follicular phase (FP). METHODS: Seven women performed 15- and 45-min cycling bouts on separate occasions (60% [Formula see text], 35 °C) followed by a [Formula see text] test during the FP and LP. CV drift was measured between 15 and 45 min during the 45-min bout, and the 15-min bout was for measuring [Formula see text] over the same time interval that CV drift occurred. RESULTS: Core temperature during LP was ~ 0.3 °C higher than FP (P < 0.05), but changes from rest during exercise were similar between phases (all P > 0.05). Heart rate increased significantly over time but was not different between phases (P = 0.78). Stroke volume decreased more over time during LP compared to FP (P = 0.02), but the values were similar at the end of exercise between phases (both time points P > 0.05). [Formula see text] decrements for FP (13%) and LP (16%) were also comparable (P = 0.97). CONCLUSIONS: The LP-FP difference in core temperature in this study was not sufficient to amplify CV strain and decrements in [Formula see text]. Greater differences in core temperature may be required to independently modulate CV drift and accompanying decrements in [Formula see text] during prolonged exercise heat stress.