A within‐subject comparison of changes in core temperature with hypoxia‐induced manipulations of relative exercise intensity
Bibliographic record
Abstract
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.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".