title: A comparison of thermoregulatory responses to exercise between mass-matched groups with large differences in body fat.
abstract: We sought to determine 1) the influence of adiposity on thermoregulatory responses independently of the confounding biophysical factors of body mass and metabolic heat production (Hprod); and 2) whether differences in adiposity should be accounted for by prescribing an exercise intensity eliciting a fixed Hprod per kilogram of lean body mass (LBM). Nine low (LO-BF) and nine high (HI-BF) body fat males matched in pairs for total body mass (TBM; LO-BF: 88.7 ± 8.4 kg, HI-BF: 90.1 ± 7.9 kg; P = 0.72), but with distinctly different percentage body fat (%BF; LO-BF: 10.8 ± 3.6%; HI-BF: 32.0 ± 5.6%; P < 0.001), cycled for 60 min at 28.1 ± 0.2 °C, 26 ± 8% relative humidity (RH), at a target Hprod of 1) 550 W (FHP trial) and 2) 7.5 W/kg LBM (LBM trial). Changes in rectal temperature (ΔTre) and local sweat rate (LSR) were measured continuously while whole body sweat loss (WBSL) and net heat loss (Hloss) were estimated over 60 min. In the FHP trial, ΔTre (LO-BF: 0.66 ± 0.21 °C, HI-BF: 0.87 ± 0.18 °C; P = 0.02) was greater in HI-BF, whereas mean LSR (LO-BF 0.52 ± 0.19, HI-BF 0.43 ± 0.15 mg·cm(-2)·min(-1); P = 0.19), WBSL (LO-BF 586 ± 82 ml, HI-BF 559 ± 75 ml; P = 0.47) and Hloss (LO-BF 1,867 ± 208 kJ, HI-BF 1,826 ± 224 kJ; P = 0.69) were all similar. In the LBM trial, ΔTre (LO-BF 0.82 ± 0.18 °C, HI-BF 0.54 ± 0.19 °C; P < 0.001), mean LSR (LO-BF 0.59 ± 0.20, HI-BF 0.38 ± 0.12 mg·cm(-2)·min(-1); P = 0.04), WBSL (LO-BF 580 ± 106 ml, HI-BF 381 ± 68 ml; P < 0.001), and Hloss (LO-BF 1,884 ± 277 kJ, HI-BF 1,341 ± 184 kJ; P < 0.001) were all greater at end-exercise in LO-BF. In conclusion, high %BF individuals demonstrate a greater ΔTre independently of differences in mass and Hprod, possibly due to a lower mean specific heat capacity or impaired sudomotor control. However, thermoregulatory responses of groups with different adiposity levels should not be compared using a fixed Hprod in watts per kilogram lean body mass.
authors.affiliation: School of Human Kinetics, University of Ottawa, Ottawa, Canada;
authors.forename: Sheila
authors.initials: S
authors.lastname: Dervis
authors.affiliation: School of Human Kinetics, University of Ottawa, Ottawa, Canada;
authors.forename: Geoff B
authors.initials: GB
authors.lastname: Coombs
authors.affiliation: Thermal Ergonomics Laboratory, Faculty of Health Sciences, University of Sydney, Sydney, New South Wales, Australia; and.
authors.forename: Georgia K
authors.initials: GK
authors.lastname: Chaseling
authors.affiliation: Thermal Ergonomics Laboratory, Faculty of Health Sciences, University of Sydney, Sydney, New South Wales, Australia; and.
authors.forename: Davide
authors.initials: D
authors.lastname: Filingeri
authors.affiliation: School of Human Kinetics, University of Ottawa, Ottawa, Canada;
authors.forename: Jovana
authors.initials: J
authors.lastname: Smoljanic
authors.affiliation: School of Human Kinetics, University of Ottawa, Ottawa, Canada; Thermal Ergonomics Laboratory, Faculty of Health Sciences, University of Sydney, Sydney, New South Wales, Australia; and Charles Perkins Centre, University of Sydney, New South Wales, Australia ollie.jay@sydney.edu.au.
authors.forename: Ollie
authors.initials: O
authors.lastname: Jay
mesh_terms: D000273:Adipose Tissue / Q000502:physiology*; D050154:Adiposity / Q000502:physiology; D000328:Adult; D015992:Body Mass Index; D001831:Body Temperature / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D006358:Hot Temperature; D006801:Humans; D008297:Male; D013546:Sweating / Q000502:physiology; D022722:Thermogenesis / Q000502:physiology; D055815:Young Adult
keywords: adiposity; biophysics; heat balance; sweating; temperature regulation