Date of Graduation

5-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Health, Sport and Exercise Science (PhD)

Degree Level

Graduate

Department

Health, Human Performance and Recreation

Advisor/Mentor

McDermott, Brendon P.

Committee Member

Charkoudian, Nisha

Second Committee Member

Ganio, Matthew S.

Third Committee Member

Greene, Nicholas P.

Keywords

Female Physiology; Fluid Regulation; Hormonal Fluctuations; Hydration; Menstrual Cycle; Thermoregulation

Abstract

Purpose: The purpose of this investigation was to evaluate the effects of combined (estradiol and progestin) monophasic oral contraceptive pill (OCP) use on thermoregulation. Further, we sought to evaluate OCP use on acute rehydration post-exercise in the heat using recommended rehydration guidelines. Methods: Twelve healthy, aerobically trained (VO2peak = 47.8 ± 4.7 mL/kg/min), long term female oral contraceptive users completed a familiarization trial and two experimental days separated by ≥ 7 days. The two experimental trials were identical except for the hormone dosing phase. One trial was completed during the third week of active pill dosing (ACT) and one during the placebo week (PLA) of their normally prescribed OCPs. Participants completed 90 minutes of cycling in 30ºC and 55% relative humidity and a rehydration protocol. Exercise intensity was set at 55% of the wattage attained during the final stage of the VO2peak test. Trec, heart rate, blood pressure and perceptual measurements were recorded every 15-minutes. Body mass change was measured continuously and recorded every 15-minutes and subsequently used to provide water (warmed to 38°C) to replace sweat losses. Water was given to the participant to match 50% of sweat loss at each time point. Metabolic data (VO2) wattage and cadence was collected at 30-minutes, 60-minutes, 75-minutes and at the cessation of exercise (Hashimoto et al., 2016) to ensure work intensity was kept constant. 125% of fluid lost was replaced via a recovery beverage and water post-exercise. Results: Tre demonstrated a significant main effect difference for ACT to be greater than PLA compared to PLA (F1.55,15.53 = 74.019, P < 0.001). There was also a significant main effect for Tre to increase over time, regardless of trial (F1,10 = 24.064, P < 0.001). There was not an interaction of time x trial (F1.96,19.62 = 1.822, P = 0.189) for Tre. There was no difference in overall change in temperature (baseline to maximum temperature) between trials (ACT: 1.3 ± 0.5ºC, PLA: 1.4 ± 0.4ºC, t10 = -0.588, P = 0.570). Post-exercise, there was no difference between trials in the amount of fluid consumed (ACT: 1007 ± 256 mL; PLA: 921 ± 448 mL, t10 = 0.874, P = 0.403). There was no difference in spot sample USG assessed 3-h post-trial between trials (t7 = -0.743, P = 0.487). Likewise, 3-h spot sample urine osmolality was not different between trials (t7 = - 1.177, P = 0.287). Urgency to void at 3-h post-trial was not different between groups (t7 = - 1.000, P = 0.351). Perception of thirst was not different 3-h post-trial (t7 = - 0.3859, P = 0.711). Conclusion: We demonstrated a significant difference in core temperature elevation during the ACT trial. However, in following recommended hydration guidelines, OCP phase has no effect on fluid retention post-exercise in the heat.

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