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Menstrual cycle and oral contraceptive use do not modify postexercise heat loss responses

¹Laboratory of Human Bioenergetics and Environmental Physiology, School of Human Kinetics, and ⁴Health Services, University of Ottawa, Ottawa, Ontario, Canada; ³Dalhousie Medical School, Dalhousie University, Faculty of Medicine, Halifax, Nova Scotia; and ²University of Calgary, Faculties of Medicine and Kinesiology, Departments of Medicine and Cardiac Sciences, Calgary, Alberta, Canada

Submitted 18 February 2008 ; accepted in final form 7 August 2008

It is unknown whether menstrual cycle or oral contraceptive (OC) use influences nonthermal control of postexercise heat loss responses. We evaluated the effect of menstrual cycle and OC use on the activation of heat loss responses during a passive heating protocol performed pre- and postexercise. Women without OC (n = 8) underwent pre- and postexercise passive heating during the early follicular phase (FP) and midluteal phase (LP). Women with OC (n = 8) underwent testing during the active pill consumption (high exogenous hormone phase, HH) and placebo (low exogenous hormone phase, LH) weeks. After a 60-min habituation at 26°C, subjects donned a liquid conditioned suit. Mean skin temperature was clamped at 32.5°C for 15 min and then gradually increased, and the absolute esophageal temperature at which the onset of forearm vasodilation (Th_VD) and upper back sweating (Th_SW) were noted. Subjects then cycled for 30 min at 75% O_{2 peak} followed by a 15-min seated recovery. A second passive heating was then performed to establish postexercise values for Th_VD and Th_SW. Between 2 and 15 min postexercise, mean arterial pressure (MAP) remained significantly below baseline (P < 0.05) by 10 ± 1 and 11 ± 1 mmHg for the FP/LH and LP/HH, respectively. MAP was not different between cycle phases. During LP/HH, Th_VD was 0.16 ± 0.24°C greater than FP/LH preexercise (P = 0.020) and 0.15 ± 0.23°C greater than FP/LH postexercise (P = 0.017). During LP/HH, Th_SW was 0.17 ± 0.23°C greater than FP/LH preexercise (P = 0.016) and 0.18 ± 0.16°C greater than FP/LH postexercise (P = 0.001). Postexercise thresholds were significantly greater (P 0.001) than preexercise during both FP/LH (Th_VD, 0.22 ± 0.03°C; Th_SW, 0.13 ± 0.03°C) and LP/HH (Th_VD, 0.21 ± 0.03°C; Th_SW, 0.14 ± 0.03°C); however, the effect of exercise was similar between LP/HH and FP/LH. No effect of OC use was observed. We conclude that neither menstrual cycle nor OC use modifies the magnitude of the postexercise elevation in Th_VD and Th_SW.

thermoregulation; body temperature; estrogen; progesterone; postexercise hypotension