Waldron et al. 2021, Heat acclimation and VO2max: meta-analysis and meta-regression

A meta-analysis and meta-regression of 28 studies compared heat acclimation and acclimatisation against exercise-alone controls in both hot and thermoneutral environments. Heat acclimation produced a small but positive thermoneutral VO₂max effect (Hedges’ g = 0.30 versus control), suggesting a modest rather than absent cool-condition benefit in trained athletes, while the hot-condition benefit remained clear. Evidence is moderate.