title: The optimal exercise intensity for the unbiased comparison of thermoregulatory responses between groups unmatched for body size during uncompensable heat stress.
abstract: We sought to identify the appropriate exercise intensity for unbiased comparisons of changes in rectal temperature (ΔTre) and local sweat rates (LSR) between groups unmatched for body size during uncompensable heat stress. Sixteen males vastly different in body morphology were separated into two equal groups [small (SM): 65.8 ± 6.2 kg, 1.8 ± 0.1 m2; large (LG): 100.0 ± 13.1 kg, 2.3 ± 0.1 m2], but matched for sudomotor thermosensitivity (SM: 1.3 ± 0.6; LG: 1.1 ± 0.4 mg·cm-2·min-1·°C-1). The maximum potential for evaporation (Emax) for each participant was assessed using an incremental humidity protocol. On separate occasions, participants then completed 60 min of cycling in a 35°C and 70% RH environment at (1) 50% of VO2max, (2) a heat production (Hprod) of 520 W, (3) Hprodrelative to mass (6 W·kg-1), and (4) Hprodrelative to mass above Emax(3 W·kg-1>Emax). Emaxwas similar between LG (347 ± 39 W, 154 ± 15 W·m-2) and SM (313 ± 63 W, 176 ± 34 W·m-2,P>0.12). ΔTrewas greater in SM compared to LG at 520 W (SM: 1.5 ± 0.5; LG 0.8 ± 0.3°C,P<0.001) and at 50% of VO2max(SM: 1.4 ± 0.5; LG 0.9 ± 0.3°C,P<0.001). However, ΔTrewas similar between groups when Hprodwas either 6 W·kg-1(SM: 0.9 ± 0.3; LG 0.9 ± 0.2°C,P=0.98) and 3 W·kg-1>Emax(SM: 1.4 ± 0.5; LG 1.3 ± 0.4°C,P=0.99). LSR was similar between LG and SM irrespective of condition, suggesting maximum LSR was attained (SM: 1.10 ± 0.23; LG: 1.07 ± 0.35 mg·cm-2·min-1,P=0.50). In conclusion, systematic differences in ΔTreand LSR between groups unmatched for body size during uncompensable heat stress can be avoided by a fixed Hprodin W·kg-1or W·kg-1>Emax.
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.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Ravanelli
authors.affiliation: School of Human Kinetics, University of Ottawa, Ottawa, Canada.|Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, Dallas, Texas.|The University of Texas Southwestern Medical Center, Texas Health Presbyterian Hospital, Dallas, Texas.
authors.forename: Matthew
authors.initials: M
authors.lastname: Cramer
authors.affiliation: School of Human Kinetics, University of Ottawa, Ottawa, Canada.
authors.forename: Pascal
authors.initials: P
authors.lastname: Imbeault
authors.affiliation: Thermal Ergonomics Laboratory, Faculty of Health Sciences, University of Sydney, Sydney, New South Wales, Australia ollie.jay@sydney.edu.au.|Charles Perkins Centre, University of Sydney, Sydney, New South Wales, Australia.
authors.forename: Ollie
authors.initials: O
authors.lastname: Jay
mesh_terms: D000328:Adult; D049628:Body Size / Q000502:physiology*; D001831:Body Temperature / Q000502:physiology*; D001833:Body Temperature Regulation / Q000502:physiology*; D015444:Exercise / Q000502:physiology*; D005260:Female; D018882:Heat Stress Disorders / Q000503:physiopathology*; D006358:Hot Temperature; D006801:Humans; D008297:Male; D013546:Sweating / Q000502:physiology*; D055815:Young Adult
keywords: Body morphology; core temperature; evaporation; hyperthermia; sweating