The Independent Influence of Large Differences in Adiposity on Thermoregulatory Responses during Exercise

Abstract

Currently no previous study has isolated the independent influence of body fat (BF) on thermoregulatory responses from the confounding biophysical factors of body mass and metabolic heat production (Hprod). Therefore, seven lean (L, BF:10.7 ± 4.1%) and seven non-lean (NL, BF:32.2 ± 6.4%) males matched for total body mass (TBM, L: 87.8 ± 8.5 kg, NL: 89.4 ± 7.8 kg; P= 0.73), cycled for 60 min in a 28.2 ±0.2˚C and 27 ± 10% RH room at i) a Hprod of 546 W; and ii) a Hprod of 7.5 W·kg lean body mass (LBM). Rectal (Tre) and esophageal (Tes) temperatures, and local sweat rate (LSR) were measured continuously; while whole body sweat loss (WBSL) was measured from 0-60 mins. At 546 W, changes in Tre (L: 0.74 ± 0.16ºC, NL: 0.83 ± 0.14ºC), mean local sweat rate (MLSR) based on an average of upper-back and forearm local sweat rates (L: 0.65 ± 0.25, NL: 0.59±0.12 mgcm-2min-1) and WBSL (L: 568 ± 28 mL, NL: 567 ± 29 mL) were similar (P>0.58). At 7.5 W·kg LBM, the L group had greater changes in Tre (L: 0.87 ± 0.16ºC, NL: 0.55 ± 0.11ºC), MLSR (L: 0.83 ±0 .38, NL: 0.41 ± 0.13 mgcm-2min-1) and WBSL (L: 638 ± 19 mL, NL: 399 ± 17 mL) (P<0.05). In conclusion, i) body fat does not independently alter thermoregulatory responses during exercise; ii) core temperature comparisons between groups differing in BF should be performed using a Hprod normalized for TBM, not LBM.