The effect of short-term heat acclimation with a permissive dehydration stimulus in female team sports players

Gritt, Jarrod S.

Abstract

Introduction: Repeated heat exposure can facilitate physiological adaptation to heat during intermittent exercise; however, there is limited information available regarding female cohorts. This has implications on the health and safety guidelines for females during heat exposure. Studies using short-term heat acclimation (STHA) with permissive dehydration have reported improved physiological response and performance during heat exposure but have tended to use male participants. Therefore, the aim of this study was to investigate the efficacy of STHA over 5-days using the controlled hyperthermia technique (with permissive dehydration), on an intermittent heat stress test (HST), using a female cohort and controlling for menstrual cycle.

Methods: Eight healthy, active, moderately trained females (mean [SD]; age 22.6 [3.0] y; height 166.2 [6.0] cm; body mass 62.3 [9.0] kg; VO2 max 43.2 [8.2] mL.kg-1.min-1). The HST (31.0˚C, 50% RH) consisted of 9x5min (45 mins) of intermittent exercise (individualised standing, walking, jogging, low-, medium-, and high-intensity running on a motorised treadmill) finishing with a 6s maximal sprint on a cycle ergometer. The exercise intensities were adapted from the match-play dynamics of female collegiate football players. Participants completed two HSTs (HST1 and HST2), separated by one week, with no STHA, as a control (C) trial. This was followed by 90 mins dehydration (no fluid), heat acclimation for 5 consecutive days (39.5˚C, 60% RH), using the controlled hyperthermia technique (rectal temperature [Tre] 38.5˚C). Participants completed a final HST (HST3), within one week of the STHA. The HST2 and HST3 trials were in the same week of each participant’s menstrual phase determined by self-reported menstrual cycle and plasma 17β-estradiol.

Results: Post (HST3) vs. Pre- (HST2) STHA, showed a reduced rectal temperature (Tre) at 45-min by 0.20˚C (95%CI: -0.31 to -0.05˚C; p = 0.01; d = 1.13); mean skin temperature ( sk T ) (-0.47; -0.82 to -0.12°C; P = 0.02; d = 1.06) and mean body temperature ( b T ) (-0.21; -0.31 to -0.11°C; P = 0.001; d = 1.28). There was limited change (P > 0.05) for these measures in the HST1 vs. HST2 C trial. Resting cardiac frequency decreased by 11 b.min-1 (-16 to -5 b.min-1; P = 0.004; d = 0.81) and by 3 b.min-1 at 45-min (-8 to 0 b.min-1; P = 0.07; d = 0.65). There was an increase in percentage plasma volume (%PV) change post-STHA by 8.65% (-1.21 to 18.51%; P = 0.007; d = 1.26) but limited change in C (P > 0.05). There was an increase in mean average power (MAvP) across all 9 sprints by 41W (3 to 80W; P = 0.04; d = 0.18) but limited change in C (P > 0.05).

Discussion and conclusion: Short-term heat acclimation (5 days), with permissive dehydration, using the controlled-hyperthermia technique leads to
physiological adaptation during intermittent exercise in the heat, in moderately trained females when controlling for menstrual cycle.

Citation

Gritt, J. S. The effect of short-term heat acclimation with a permissive dehydration stimulus in female team sports players. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4221873

• Thesis Type: Thesis
• Deposit Date: Oct 15, 2019
• Publicly Available Date: Feb 23, 2023
• Keywords: Sports science
• Public URL: https://hull-repository.worktribe.com/output/4221873
• Additional Information: Department of Sport, Health and Exercise Science, The University of Hull
• Award Date: Jul 1, 2017