Influence of Menstrual Cycle Phase on Cardiovascular Drift and Maximal Oxygen Uptake During Heat Stress

983 Board #217 May 29 2:00 PM - 3:30 PM

Cardiovascular drift (CV drift) is related to reduced maximal oxygen uptake (V̇O_2max) during heat stress. Whether this relationship is modified by elevated core temperature during the luteal phase (LP) of the menstrual cycle remains unknown.

PURPOSE: To test the hypothesis that the magnitude of CV drift and accompanying decrement in V̇O_2max is greater during the LP of the menstrual cycle vs. the follicular phase (FP).

METHODS: Seven women (mean±SD; age=24±5 y) completed a graded exercise test in ~22 °C to determine V̇O_2max, followed by one 15-min and one 45-min trial at 60% V̇O_2max in 35 °C—each immediately followed by measurement of V̇O_2max—in the FP and LP. CV drift was measured between 15 and 45 min during the 45-min trials. The purpose of the separate 15- and 45-min trials was to measure CV drift and V̇O_2max over the same time interval.

RESULTS: Rectal temperature (T_re) at rest and during exercise was higher in the LP (p<0.05). Heart rate increased 9% between 15 and 45 min in both phases (p=0.71), while stroke volume decreased more in the LP (-18%) compared to the FP (-11%; p<0.001). V̇O_2max decreased significantly over time (p=0.002), but menstrual cycle phases were not different (16% and 13% for LP and FP, respectively, p=0.28).

CONCLUSION: Greater thermal strain in the LP compared to the FP did not modulate the relationship between CV drift and V̇O_2max during exercise in the heat.