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Effect of hypohydration on thermoregulatory responses in men with low and high body fat exercising in the heat.
J Appl Physiol (1985). 2017 01 01; 122(1):142-152.JA

Abstract

It is unclear whether men with low body fat (LO-BF) have impaired thermoregulation during exercise heat stress compared with those with high body fat (HI-BF) when euhydration (EU) is maintained. Furthermore, in LO-BF individuals, hypohydration (HY) impairs thermoregulatory responses during exercise heat stress, but it is unknown whether this occurs in HI-BF counterparts. The purpose of this study was to test the hypotheses that men with HI-BF have impaired thermoregulatory responses to exercise heat stress and that HY further exacerbates these impairments vs. LO-BF. Men with LO-BF [n = 11, body mass (BM) 73.9 ± 8.5 kg, BF% 13.6 ± 3.8] and HI-BF (n = 9, BM 89.6 ± 6.9 kg, BF% 30.2 ± 4.1), in a randomized crossover design, performed 60 min of upright cycling in a hot environment (40.3 ± 0.4°C, relative humidity 32.5 ± 1.9%) at a metabolic heat production rate of 6 W/kg BM and finished exercise either euhydrated (EU; 0.3 ± 1.2 vs. 0.3 ± 0.9% BM loss) or HY (-2.5 ± 1.1 vs. -1.7 ± 1.5% BM loss). Changes in rectal temperature (ΔTrec), local sweat rate (ΔLSR), and cutaneous vascular conductance (ΔCVC; %max) were measured throughout. When EU, LO-BF and HI-BF had similar CVC and LSR responses (P > 0.05); however, LO-BF had a lower ΔTrec vs. HI-BF (0.92 ± 0.35 vs. 1.31 ± 0.32°C, P = 0.021). Compared with EU, HY increased end-exercise ΔTrec in LO-BF (0.47 ± 0.37°C, P < 0.01) but not in HI-BF (-0.06 ± 0.29°C, P > 0.05). HY, compared with EU, did not affect ΔLSR and ΔCVC in either group (P > 0.05). We conclude that, when euhydrated, men with HI-BF have a greater increase in Trec vs. LO-BF but similar CVC and LSR. HY exacerbates increases in Trec in LO-BF but not HI-BF.

NEW & NOTEWORTHY

This is the first known investigation to compare thermoregulatory responses to exercise heat stress between men with high and low body fat (BF) in a physiologically uncompensable environment while simultaneously examining the confounding influence of hydration status. Both groups demonstrated similar sweating and cutaneous vasodilatory responses when euhydrated, despite vast differences in rectal temperature. Furthermore, in contrast to low BF, individuals with high BF demonstrated similar increases in core body temperature when either euhydrated or hypohydrated.

Authors+Show Affiliations

Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.Department of Rehabilitation, Human Resources, and Communication Disorders, University of Arkansas, Fayetteville, Arkansas.Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and msganio@uark.edu.

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

27789773

Citation

Tucker, Matthew A., et al. "Effect of Hypohydration On Thermoregulatory Responses in Men With Low and High Body Fat Exercising in the Heat." Journal of Applied Physiology (Bethesda, Md. : 1985), vol. 122, no. 1, 2017, pp. 142-152.
Tucker MA, Caldwell AR, Butts CL, et al. Effect of hypohydration on thermoregulatory responses in men with low and high body fat exercising in the heat. J Appl Physiol (1985). 2017;122(1):142-152.
Tucker, M. A., Caldwell, A. R., Butts, C. L., Robinson, F. B., Reynebeau, H. C., Kavouras, S. A., McDermott, B. P., Washington, T. A., Turner, R. C., & Ganio, M. S. (2017). Effect of hypohydration on thermoregulatory responses in men with low and high body fat exercising in the heat. Journal of Applied Physiology (Bethesda, Md. : 1985), 122(1), 142-152. https://doi.org/10.1152/japplphysiol.00768.2016
Tucker MA, et al. Effect of Hypohydration On Thermoregulatory Responses in Men With Low and High Body Fat Exercising in the Heat. J Appl Physiol (1985). 2017 01 1;122(1):142-152. PubMed PMID: 27789773.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Effect of hypohydration on thermoregulatory responses in men with low and high body fat exercising in the heat. AU - Tucker,Matthew A, AU - Caldwell,Aaron R, AU - Butts,Cory L, AU - Robinson,Forrest B, AU - Reynebeau,Haley C, AU - Kavouras,Stavros A, AU - McDermott,Brendon P, AU - Washington,Tyrone A, AU - Turner,Ronna C, AU - Ganio,Matthew S, Y1 - 2016/10/27/ PY - 2016/08/31/received PY - 2016/10/26/revised PY - 2016/10/26/accepted PY - 2016/11/1/pubmed PY - 2017/12/20/medline PY - 2016/11/1/entrez KW - cutaneous vasodilation KW - exercise heat stress KW - obesity KW - sweating KW - temperature regulation SP - 142 EP - 152 JF - Journal of applied physiology (Bethesda, Md. : 1985) JO - J Appl Physiol (1985) VL - 122 IS - 1 N2 - : It is unclear whether men with low body fat (LO-BF) have impaired thermoregulation during exercise heat stress compared with those with high body fat (HI-BF) when euhydration (EU) is maintained. Furthermore, in LO-BF individuals, hypohydration (HY) impairs thermoregulatory responses during exercise heat stress, but it is unknown whether this occurs in HI-BF counterparts. The purpose of this study was to test the hypotheses that men with HI-BF have impaired thermoregulatory responses to exercise heat stress and that HY further exacerbates these impairments vs. LO-BF. Men with LO-BF [n = 11, body mass (BM) 73.9 ± 8.5 kg, BF% 13.6 ± 3.8] and HI-BF (n = 9, BM 89.6 ± 6.9 kg, BF% 30.2 ± 4.1), in a randomized crossover design, performed 60 min of upright cycling in a hot environment (40.3 ± 0.4°C, relative humidity 32.5 ± 1.9%) at a metabolic heat production rate of 6 W/kg BM and finished exercise either euhydrated (EU; 0.3 ± 1.2 vs. 0.3 ± 0.9% BM loss) or HY (-2.5 ± 1.1 vs. -1.7 ± 1.5% BM loss). Changes in rectal temperature (ΔTrec), local sweat rate (ΔLSR), and cutaneous vascular conductance (ΔCVC; %max) were measured throughout. When EU, LO-BF and HI-BF had similar CVC and LSR responses (P > 0.05); however, LO-BF had a lower ΔTrec vs. HI-BF (0.92 ± 0.35 vs. 1.31 ± 0.32°C, P = 0.021). Compared with EU, HY increased end-exercise ΔTrec in LO-BF (0.47 ± 0.37°C, P < 0.01) but not in HI-BF (-0.06 ± 0.29°C, P > 0.05). HY, compared with EU, did not affect ΔLSR and ΔCVC in either group (P > 0.05). We conclude that, when euhydrated, men with HI-BF have a greater increase in Trec vs. LO-BF but similar CVC and LSR. HY exacerbates increases in Trec in LO-BF but not HI-BF. NEW & NOTEWORTHY: This is the first known investigation to compare thermoregulatory responses to exercise heat stress between men with high and low body fat (BF) in a physiologically uncompensable environment while simultaneously examining the confounding influence of hydration status. Both groups demonstrated similar sweating and cutaneous vasodilatory responses when euhydrated, despite vast differences in rectal temperature. Furthermore, in contrast to low BF, individuals with high BF demonstrated similar increases in core body temperature when either euhydrated or hypohydrated. SN - 1522-1601 UR - https://www.unboundmedicine.com/medline/citation/27789773/Effect_of_hypohydration_on_thermoregulatory_responses_in_men_with_low_and_high_body_fat_exercising_in_the_heat_ L2 - https://journals.physiology.org/doi/10.1152/japplphysiol.00768.2016?url_ver=Z39.88-2003&amp;rfr_id=ori:rid:crossref.org&amp;rfr_dat=cr_pub=pubmed DB - PRIME DP - Unbound Medicine ER -