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Effect of Permissive Dehydration on Induction and Decay of Heat Acclimation, and Temperate Exercise Performance.
Front Physiol 2016; 7:564FP

Abstract

Purpose:

It has been suggested that dehydration is an independent stimulus for heat acclimation (HA), possibly through influencing fluid-regulation mechanisms and increasing plasma volume (PV) expansion. There is also some evidence that HA may be ergogenic in temperate conditions and that this may be linked to PV expansion. We investigated: (i) the influence of dehydration on the time-course of acquisition and decay of HA; (ii) whether dehydration augmented any ergogenic benefits in temperate conditions, particularly those related to PV expansion. Methods: Eight males [VO2max: 56.9(7.2) mL·kg-1·min-1] undertook two HA programmes (balanced cross-over design), once drinking to maintain euhydration (HAEu) and once with restricted fluid-intake (HADe). Days 1, 6, 11, and 18 were 60 min exercise-heat stress tests [HST (40°C; 50% RH)], days 2-5 and 7-10 were 90 min, isothermal-strain (Tre ~ 38.5°C), exercise-heat sessions. Performance parameters [VO2max, lactate threshold, efficiency, peak power output (PPO)] were determined pre and post HA by graded exercise test (22°C; 55%RH). Results: During isothermal-strain sessions hypohydration was achieved in HADe and euhydration maintained in HAEu [average body mass loss -2.71(0.82)% vs. -0.56(0.73)%, P < 0.001], but aldosterone concentration, power output, and cardiovascular strain were unaffected by dehydration. HA was evident on day 6 {reduced end-exercise Tre [-0.30(0.27)°C] and exercise heart rate [-12(15) beats.min-1], increased PV [+7.2(6.4)%] and sweat-loss [+0.25(0.22) L.h-1], P < 0.05} with some further adaptations on day 11 {further reduced end-exercise Tre [-0.25(0.19)°C] and exercise heart rate [-3(9) beats.min-1], P < 0.05}. These adaptations were not notably affected by dehydration and were generally maintained 7-days post HA. Performance parameters were unchanged, apart from increased PPO (+16(20) W, irrespective of condition). Conclusions: When thermal-strain is matched, permissive dehydration which induces a mild, transient, hypohydration does not affect the acquisition and decay of HA, or endurance performance parameters. Irrespective of hydration, trained individuals require >5 days to optimize HA.

Authors+Show Affiliations

Extreme Environments Laboratory, Department of Sport and Exercise Sciences, University of Portsmouth Portsmouth, UK.Extreme Environments Laboratory, Department of Sport and Exercise Sciences, University of Portsmouth Portsmouth, UK.Extreme Environments Laboratory, Department of Sport and Exercise Sciences, University of Portsmouth Portsmouth, UK.Young Laboratory, School of Pharmacy and Biomedical Sciences, University of Portsmouth Portsmouth, UK.Extreme Environments Laboratory, Department of Sport and Exercise Sciences, University of Portsmouth Portsmouth, UK.

Pub Type(s)

Journal Article

Language

eng

PubMed ID

27932993

Citation

Neal, Rebecca A., et al. "Effect of Permissive Dehydration On Induction and Decay of Heat Acclimation, and Temperate Exercise Performance." Frontiers in Physiology, vol. 7, 2016, p. 564.
Neal RA, Massey HC, Tipton MJ, et al. Effect of Permissive Dehydration on Induction and Decay of Heat Acclimation, and Temperate Exercise Performance. Front Physiol. 2016;7:564.
Neal, R. A., Massey, H. C., Tipton, M. J., Young, J. S., & Corbett, J. (2016). Effect of Permissive Dehydration on Induction and Decay of Heat Acclimation, and Temperate Exercise Performance. Frontiers in Physiology, 7, p. 564.
Neal RA, et al. Effect of Permissive Dehydration On Induction and Decay of Heat Acclimation, and Temperate Exercise Performance. Front Physiol. 2016;7:564. PubMed PMID: 27932993.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Effect of Permissive Dehydration on Induction and Decay of Heat Acclimation, and Temperate Exercise Performance. AU - Neal,Rebecca A, AU - Massey,Heather C, AU - Tipton,Michael J, AU - Young,John S, AU - Corbett,Jo, Y1 - 2016/11/23/ PY - 2016/09/22/received PY - 2016/11/07/accepted PY - 2016/12/10/entrez PY - 2016/12/10/pubmed PY - 2016/12/10/medline KW - acclimatization KW - fluid KW - hydration KW - hypohydration KW - thermoregulation SP - 564 EP - 564 JF - Frontiers in physiology JO - Front Physiol VL - 7 N2 - Purpose: It has been suggested that dehydration is an independent stimulus for heat acclimation (HA), possibly through influencing fluid-regulation mechanisms and increasing plasma volume (PV) expansion. There is also some evidence that HA may be ergogenic in temperate conditions and that this may be linked to PV expansion. We investigated: (i) the influence of dehydration on the time-course of acquisition and decay of HA; (ii) whether dehydration augmented any ergogenic benefits in temperate conditions, particularly those related to PV expansion. Methods: Eight males [VO2max: 56.9(7.2) mL·kg-1·min-1] undertook two HA programmes (balanced cross-over design), once drinking to maintain euhydration (HAEu) and once with restricted fluid-intake (HADe). Days 1, 6, 11, and 18 were 60 min exercise-heat stress tests [HST (40°C; 50% RH)], days 2-5 and 7-10 were 90 min, isothermal-strain (Tre ~ 38.5°C), exercise-heat sessions. Performance parameters [VO2max, lactate threshold, efficiency, peak power output (PPO)] were determined pre and post HA by graded exercise test (22°C; 55%RH). Results: During isothermal-strain sessions hypohydration was achieved in HADe and euhydration maintained in HAEu [average body mass loss -2.71(0.82)% vs. -0.56(0.73)%, P < 0.001], but aldosterone concentration, power output, and cardiovascular strain were unaffected by dehydration. HA was evident on day 6 {reduced end-exercise Tre [-0.30(0.27)°C] and exercise heart rate [-12(15) beats.min-1], increased PV [+7.2(6.4)%] and sweat-loss [+0.25(0.22) L.h-1], P < 0.05} with some further adaptations on day 11 {further reduced end-exercise Tre [-0.25(0.19)°C] and exercise heart rate [-3(9) beats.min-1], P < 0.05}. These adaptations were not notably affected by dehydration and were generally maintained 7-days post HA. Performance parameters were unchanged, apart from increased PPO (+16(20) W, irrespective of condition). Conclusions: When thermal-strain is matched, permissive dehydration which induces a mild, transient, hypohydration does not affect the acquisition and decay of HA, or endurance performance parameters. Irrespective of hydration, trained individuals require >5 days to optimize HA. SN - 1664-042X UR - https://www.unboundmedicine.com/medline/citation/27932993/Effect_of_Permissive_Dehydration_on_Induction_and_Decay_of_Heat_Acclimation_and_Temperate_Exercise_Performance_ L2 - https://dx.doi.org/10.3389/fphys.2016.00564 DB - PRIME DP - Unbound Medicine ER -