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Effectiveness of short-term heat acclimation on intermittent performance in cold and hot environments

Nation, Fiona

Authors

Fiona Nation



Contributors

A.T. Garrett
Supervisor

Abstract

Introduction: It is well-established that repetition of heat stress exposure has been shown to facilitate adaptations to the heat but these protocols have tended to be of a fixed work intensity, continuous exercise, long-term in duration (>7 days) and use hydration. Secondly, there is limited information on the potential use of heat acclimation as a training method for human performance in cool/thermoneutral conditions (Corbett, Neal, Lunt, & Tipton, 2014). Therefore, the aims of this study were to investigate the effectiveness of short-term heat acclimation (STHA) for 5 days, using the controlled-hyperthermia technique with dehydration, on intermittent exercise in cool and hot environments. Methods: Ten, healthy, active, moderately-trained males (Mean (SD); Age 25.6 (8.9) yrs; Height 180.7 (5.6) cm; Body Mass 83.2 (10.8) kg; 45.3 (6.5) mL.kg-1.min-1 and resting cardiac output 6.3 (1.8) L.min-1), participated in a STHA programme. This consisted of 90 minutes dehydration heat acclimation (no fluid intake) for 5 consecutive days (39.5°C; 60% RH), using the controlled hyperthermia technique (~rectal temperature [Tre] 38.5°C) (Garrett et al., 2014). The pre and post testing Exercise Stress Test (EST) consisted of 45 minutes of intermittent exercise (nine phases of 5 minutes). Including resting, walking, moderate and high intensity running) on a motorised, h/p Cosmos treadmill; and nine 6 second (s) maximal sprints on a Watt Bike, as a repeated, maximal sprint performance test. The EST was followed by a running, incremental test to exhaustion. This EST intermittent protocol was adapted from exercise intensities of professional football players (Drust, Reilly, & Cable, 2000). The EST was repeated in controlled conditions (Con; 11°C 45% RH); pre and post STHA in cool (C; 11°C 45% RH) and hot environments (H; 35°C 45% RH). Data analysis was by paired t-test. Reported as the mean differences with 95% confidence intervals (95%CI) and Cohen’s d effect size for magnitude of change (ES; Where 0.2-0.6 small; 0.6-1.2 moderate; 1.2-2.0 large; 2.0-4.0 very large). Results: Post STHA, in the H trial at 45-min there was a decrease in Tre by -0.2°C (95%CI: -0.40 to 0.00°C; p=0.03; ES= -0.56), cardiac frequency (-3: -5 to -1 b.min-1; p=0.01; ES= -0.20) and RPE (-2: -3 to -1 units; p=0.01; ES=-0.56). Mean average power (MavP) increased in sprints 7 (111: 25 to 197 W; p=0.01; ES=0.93) and 9 (240: 9 and 489 W; p=0.04; ES=0.77). The increase in Sprint 8 (87: -8 to 182 W; p=0.06; ES=0.52) and time to exhaustion (208: -24 to 439 s; p=0.06; ES=0.63) were close to significance. In the C trial, increased MavP for sprint 9 (67: 2 to 131 W; p=0.04; ES=0.47) and time to exhaustion (43: 1 to 85 s; p=0.04; ES=0.32) were reported. There was limited change in the Con conditions across all nine sprints (p>0.05) and for time to exhaustion (-31: -72 to 11 s; p=0.12; ES=- 0.18). Discussion: Short-term heat acclimation (5 days) with dehydration, using the controlled-hyperthermia technique, is effective for physiological adaptations during intermittent exercise in a hot environment. Furthermore, it has resulted in an increase in intermittent and endurance exercise performance in hot and cool conditions. Conclusion: Short-term heat acclimation is effective for intermittent exercise in the heat. It may be a useful training method for human performance in cool conditions.

Citation

Nation, F. (2015). Effectiveness of short-term heat acclimation on intermittent performance in cold and hot environments. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4218607

Thesis Type Thesis
Deposit Date Oct 31, 2016
Publicly Available Date Mar 29, 2024
Keywords Sports sciences
Public URL https://hull-repository.worktribe.com/output/4218607
Additional Information Department of Sport, Health and Exercise Science, The University of Hull
Award Date Oct 1, 2015

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Copyright Statement
© 2015 Nation, Fiona. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright holder.




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