Effects Of Dehydration And Menstrual Cycle Phase On Sweat Rate In A Hot Dry Enviornment

Abstract

PURPOSE: The study was designed to examine the effects of dehydration and menstrual cycle phase on sweat rate in moderately trained women during an acute bout of aerobic exercise in a hot dry environment. METHODS: Nine moderately trained women [age 22.78 ± 2.38 yrs., (V [Combining Dot Above]O2peak) 44.11 ± 5.56 ml-1 kg-1 min-1, BF 21.08 ± 5.56] who had refrained from oral contraceptives over the past 12 months and from the morning after pill during baseline and experimental procedures performed 45 min of cycle exercise at 55-65% of V [Combining Dot Above]O2peak in a dehydrated state (USG >1.02) while having sweat rate, onset of sweat, Tr, Tsk, Tb, HR, thermal sensation and RPE measured every 5 min of exercise. All experimental sessions took place between 6:00 am and 12:00 pm. Sweat loss was estimated from pre and post exercise body weight difference. RESULTS: Sweat rate, the onset of sweat, thermal sensation and RPE were not affected by menstrual phase, however, as expected, there was a trend toward a higher sweat rate and an earlier onset of sweat in the luteal phase compared to the follicular phase in the dehydrated state. The mean sweat rate in the luteal phase was ML = 12.54 ± 4.18 ml/min and the mean sweat rate in the follicular phase was MF = 10.57 ± 2.25 min. The mean onset sweat rate time in the luteal phase was ML = 11:24 ± 1:50 min and the mean sweat rate in the follicular phase was MF = 12:34 ± 2.54 min. Mean Tc, Tsk, and Tb were higher during the luteal phase than the follicular phase at all time points (p < .05). CONCLUSION: The elevation in core temperature observed in the current study may be associated with the increase in circulating progesterone during the luteal phase of the menstrual cycle. The increase in progesterone may be potential mechanism explaining the increase in blood flow, thus, the onset of skin vasodilatation in the luteal phase, which ultimately causes skin and body temperature to rise. In conclusion, with the findings of the current study, researchers suggest that during exercise in the dehydrated state, sweat rate is reduced thereby enhancing thermoregulatory and cardiovascular demands during exercise in a hot dry environment. Future researchers may examine the effects of the menstrual cycle on exercise in a hot environment when in fact fluid replacement is controlled and hydration is maintained.