Training in the heat beat the same kind of training in thermoneutral conditions for aerobic performance in the heat (Hedges' g 0.56) and for heat adaptation
Larger falls in resting and exercise core temperature (g 0.51 and 0.55) and exercise heart rate (g 0.69), a larger rise in sweat rate (g 0.56), skin temperature not significantly different (g 0.47) — in a multilevel meta-analysis of 23 studies; the extra benefit was larger in Tier 3 athletes and longer interventions, and thermoneutral training alone also lowered exercise core temperature and heart rate
Chen and colleagues asked whether exercising in hot conditions adds anything to heat resilience beyond the same exercise in thermoneutral conditions, since some evidence suggests that thermoneutral training brings comparable adaptations.
They searched five databases to November 2025, included 23 studies, and used multilevel meta-analysis to estimate differences between hot and thermoneutral training groups and changes from baseline within each.
Compared with thermoneutral training, heat training produced larger falls in resting and exercise core temperature and exercise heart rate, a larger rise in sweat rate, and a larger gain in aerobic performance in the heat; exercise skin temperature did not differ significantly.
Against baseline, heat training improved every heat-related outcome by a moderate to large amount, while thermoneutral training significantly improved exercise core temperature and exercise heart rate. The added benefit of heat was larger in elite athletes (the authors' Tier 3) and in longer interventions; no other moderator was significant.
The authors conclude that heat exposure during training gives extra heat adaptation and aerobic performance in the heat, and that thermoneutral training still produces modest gains in key thermoregulatory and cardiovascular outcomes.
Participants
Protocol
Key Results
| Outcome | Heat vs thermoneutral training (Hedges' g) | Significant |
|---|---|---|
| Resting core temperature (reduction) | 0.51 | yes |
| Exercise core temperature (reduction) | 0.55 | yes |
| Exercise heart rate (reduction) | 0.69 | yes |
| Sweat rate (increase) | 0.56 | yes |
| Aerobic performance in the heat | 0.56 | yes |
| Exercise skin temperature | 0.47 | no |
| Within-group change from baseline | Result |
|---|---|
| Heat training | moderate-to-large improvements in all heat-related outcomes (values not in the abstract) |
| Thermoneutral training, exercise core temperature | g 0.41, significant |
| Thermoneutral training, exercise heart rate | g 0.57, significant |
| Thermoneutral training, other outcomes | not reported as significant in the abstract |
Practical Application
Limitations
How this entry was checked and changed
risk of bias not read (abstract only); a meta-analysis whose abstract reports no quality or certainty appraisal; the performance result is an outcome, while the core-temperature, heart-rate, skin-temperature and sweat-rate results are markers and would sit one step lower on their own