Whole‐body Heat Exchange in Young and Middle‐Aged Men during Constant‐ and Variable‐Intensity Work of Equivalent Metabolic Demand in Dry Heat
Bibliographic record
Abstract
Current occupational heat stress guidelines incorporate time‐weighted averaging to quantify a workers’ metabolic rate during tasks of varied intensity. Since such guidelines originate from data obtained during work at a constant (fixed) intensity, their validity relies on the assumption that constant‐ and variable‐intensity work eliciting the same time‐weighted average metabolic rate will evoke similar heat strain. We recently confirmed the veracity of this assumption in young men. However, it remains uncertain whether this holds for the rising number of middle‐aged workers, who display age‐related impairments in whole‐body total heat loss (evaporative+dry heat loss) during constant, moderate work that worsen at higher work intensities. It is possible that variable‐intensity work involving brief periods at higher intensities may exacerbate age‐related impairments in heat loss in these individuals, thereby worsening body heat storage relative to constant‐intensity work. To evaluate this hypothesis, 7 middle‐aged (mean (SD): 60 (4) years) and 8 young (25 (4) years) men completed four trials involving 90‐min of work (cycling) at an average metabolic heat production of 200 W/m 2 in dry‐heat (40°C, 20% relative humidity). Trials were administered in a random order (each separated by >48 hours) and differed only in the pattern of work performed, with one involving constant external work (40 W/m 2 ) and the others involving 10‐min cycles of varying external work: (i) 5 min at 15 W/m 2 then 5‐min at 60 W/m 2 ; (ii) 6 min at 15 W/m 2 then 4 min at 70 W/m 2 ; and (iii) 7 min at 15 W/m 2 then 3 min at 80 W/m 2 . Metabolic heat production and whole‐body total heat loss were measured via indirect and direct calorimetry (respectively), and used to derive body heat storage (summation of heat production and total heat loss). Data were averaged over each 90‐min period and compared between groups and across conditions using a mixed‐model ANOVA. Heat production was similar between groups and across conditions (group: p =.80; condition: p =.53; interaction: p =.84), averaging 205 (9) W/m 2 and 206 (7) W/m 2 in middle‐aged and young men, respectively. However, contrary to our hypothesis, total heat loss did not differ significantly between groups or across conditions (group: p =.23; condition: p =.87; interaction: p =.97), averaging 180 (8) W/m 2 and 185 (12) W/m 2 in middle‐aged and young men, respectively. As such, body heat storage was also similar between groups and across conditions (group: p =.22; condition: p =.35; interaction: p =.75), averaging 25 (9) W/m 2 and 21 (9) W/m 2 in middle‐aged and young men, respectively. In conclusion, whole‐body total heat loss and body heat storage were not significantly influenced by the partitioning of work intensity in either middle‐aged or young men, indicating that time‐weighted averaging appears to be an appropriate means of quantifying metabolic demand to assess occupational heat stress. Support or Funding Information The Government of Ontario, Canada.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".