title: Effect of hypohydration on thermoregulatory responses in men with low and high body fat exercising in the heat.
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 ΔTrecvs. HI-BF (0.92 ± 0.35 vs. 1.31 ± 0.32°C, P = 0.021). Compared with EU, HY increased end-exercise ΔTrecin 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 Trecvs. LO-BF but similar CVC and LSR. HY exacerbates increases in Trecin LO-BF but not HI-BF.
  
  
  
  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: Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.
authors: Matthew A
authors: MA
authors: Tucker
authors: Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.
authors: Aaron R
authors: 0000-0002-4541-6283
authors: AR
authors: Caldwell
authors: Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.
authors: Cory L
authors: CL
authors: Butts
authors: Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.
authors: Forrest B
authors: FB
authors: Robinson
authors: Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.
authors: Haley C
authors: HC
authors: Reynebeau
authors: Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.
authors: Stavros A
authors: 0000-0001-7485-8112
authors: SA
authors: Kavouras
authors: Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.
authors: Brendon P
authors: BP
authors: McDermott
authors: Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and.
authors: Tyrone A
authors: TA
authors: Washington
authors: Department of Rehabilitation, Human Resources, and Communication Disorders, University of Arkansas, Fayetteville, Arkansas.
authors: Ronna C
authors: RC
authors: Turner
authors: Department of Health, Human Performance, and Recreation, University of Arkansas, Fayetteville, Arkansas; and msganio@uark.edu.
authors: Matthew S
authors: MS
authors: Ganio
mesh_terms: D000273:Adipose Tissue / Q000502:physiology*; D000328:Adult; D001831:Body Temperature / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology*; D003681:Dehydration / Q000503:physiopathology*; D015444:Exercise / Q000502:physiology*; D018882:Heat Stress Disorders / Q000503:physiopathology; D006358:Hot Temperature; D006801:Humans; D008297:Male; D013546:Sweating / Q000502:physiology; D022722:Thermogenesis / Q000502:physiology; D055815:Young Adult
keywords: cutaneous vasodilation; exercise heat stress; obesity; sweating; temperature regulation