Journal
JOURNAL OF APPLIED PHYSIOLOGY
Volume 120, Issue 6, Pages 615-623Publisher
AMER PHYSIOLOGICAL SOC
DOI: 10.1152/japplphysiol.00906.2015
Keywords
adiposity; biophysics; heat balance; sweating; temperature regulation
Categories
Funding
- Natural Sciences and Engineering Research Council (NSERC) of Canada [86143-2010]
- Canadian Foundation for Innovation (CFI) Infrastructure Grant
- University of Ottawa Master's Scholarship
- Government of Australia Endeavour Postdoctoral Fellowship
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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 (H-prod); and 2) whether differences in adiposity should be accounted for by prescribing an exercise intensity eliciting a fixed H-prod 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 degrees C, 26 +/- 8% relative humidity (RH), at a target H-prod of 1) 550 W (FHP trial) and 2) 7.5 W/kg LBM (LBM trial). Changes in rectal temperature (Delta T-re) and local sweat rate (LSR) were measured continuously while whole body sweat loss (WBSL) and net heat loss (H-loss) were estimated over 60 min. In the FHP trial, Delta T-re (LO-BF: 0.66 +/- 0.21 degrees C, HI-BF: 0.87 +/- 0.18 degrees 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 H-loss (LO-BF 1,867 +/- 208 kJ, HI-BF 1,826 +/- 224 kJ; P = 0.69) were all similar. In the LBM trial, Delta T-re (LO-BF 0.82 +/- 0.18 degrees C, HI-BF 0.54 +/- 0.19 degrees 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 H-loss (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 Delta T-re 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.
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