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A within‐subject comparison of changes in core temperature with hypoxia‐induced manipulations of relative exercise intensity
Author(s) -
Coombs Geoff,
Ravanelli Nicholas,
Cramer Matthew,
Imbeault Pascal,
Jay Ollie
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1243.17
Subject(s) - exercise intensity , core temperature , chemistry , rectal temperature , zoology , vo2 max , exercise physiology , core (optical fiber) , medicine , heart rate , physics , biology , blood pressure , optics
Traditionally, relative exercise intensity (i.e., %VO 2max ) has been thought to determine changes in core temperature during exercise in compensable environments; however, recent evidence from our laboratory has suggested otherwise. Using independent group designs, we have demonstrated that to make unbiased comparisons of changes in core temperature, exercise intensities should be set to elicit a fixed metabolic heat production (H prod ) per unit of total body mass (W/kg), irrespective of large differences in %VO 2max (Jay et al. Am J Physiol. 2011) or absolute H prod (Cramer & Jay, J Appl Physiol. 2014). Using a within‐subject design, the present study assessed whether changes in core temperature during exercise at a given H prod in W/kg are altered by differences in %VO 2max , secondary to acute hypoxia exposure (~13% O 2 ) compared to normoxia (21% O 2 ). It was also assessed whether the change in core temperature during exercise at a fixed %VO 2max in hypoxic (HYP) conditions will be similar to normoxia (NORM) despite a 31±8% reduction in hypoxic VO 2max and therefore a much lower H prod . Four participants (1.78±0.04 m, 69.9±5.3 kg, 27±5 y) cycled for 45 min at 34°C, 45% RH in a climate‐controlled chamber. Measurements of esophageal temperature (T es ) and rectal temperature (T re ) were recorded every 5 s, and indirect calorimetry was recorded breath‐by‐breath. Preliminary data indicate that 45‐min ΔT es during exercise at a fixed H prod (NORM: 6.3±0.4 W/kg; HYP: 6.9±0.4 W/kg; P=0.13) were similar between conditions (NORM: 0.52±0.22°C; HYP: 0.47±0.27°C; P=0.61), while ΔT re were also similar (NORM: 0.71±0.26°C; HYP: 0.74±0.27°C; P=0.41), despite large differences in relative exercise intensity (NORM: 40±8%VO 2max ; HYP: 62±8% VO 2max ; P=0.02). However, when a subsequent bout of hypoxic exercise was normalized for %VO 2max (NORM: 40±8%VO 2max ; HYP: 46±4% VO 2max ; P=0.07), ΔT es in the hypoxic condition were lower compared to the normoxic condition (NORM: 0.52±0.22°C; HYP: 0.34±0.25°C; P<0.01) and ΔT re was lower as well (NORM: 0.71±0.26°C; HYP: 0.52±0.30°C; P=0.04) due to a lower H prod (NORM: 6.3±0.4 W/kg; HYP: 5.3±0.6 W/kg; P=0.02). In conclusion, our within‐subject comparison provides further evidence that changes in core temperature are determined by exercise at a fixed H prod in W/kg, despite large differences in relative exercise intensity, and that exercise at a fixed %VO 2max , but different H prod in W/kg, results in different changes in core temperature. Support or Funding Information This project was supported by a Discovery grant from the Natural Sciences and Engineering Research Council (NSERC) of Canada, and also in part by a research grant from the Gatorade Sports Science Institute.