The effect of post-exercise heat exposure (passive heat acclimation) on endurance exercise performance: a systematic review and meta-analysis
Sample
n=199 participants (156 male, 43 female; age 20-32 years) across 10 studies. Inclusion required healthy adults, an exercise-training intervention with post-exercise sauna or hot-water immersion, a non-heat control group doing the same training, and a performance or physiological outcome.
Key Findings
Performance in hot conditions (33-40 °C), the primary outcome: ratio of means 1.04 (95% CI 0.94-1.15, P = 0.46; 95% prediction interval 0.81-1.33) — trivial, imprecise, and the prediction interval spans a loss as well as a gain
Performance in thermoneutral conditions (18-24 °C): trivial effect
Speed at lactate threshold: trivial
VO2max, heart rate, core temperature, sweat rate: small effects
Thermal sensations: moderate effect
Certainty of evidence: low to very low for every outcome (small samples, high risk of bias, publication-bias risk, imprecision, low power)
Practical Application
Across 10 trials and 199 people, adding sauna or hot-water immersion after training changed performance in the heat by a trivial 4% (CI 0.94-1.15) with a prediction interval that includes getting worse — post-exercise passive heat is not a reliable performance enhancer; the one outcome it moves moderately is how hot the athlete feels.
The authors' conclusion: the use of post-exercise heat exposure for improving performance is uncertain; firmer trials are needed.
Not from this paper; the base's own practice: if passive heat is used at all, treat it as an adjunct to exercise-in-the-heat in a heat-prep block, not as a substitute — see REF-002 (Périard) for active heat acclimation.
Limitations
Only 10 studies included (field is young), all small
Heterogeneous protocols (sauna and hot-water immersion pooled); the abstract does not give the temperature or duration ranges of the exposures
No head-to-head sauna vs HWI vs chamber comparison in pooled data
How this entry was checked and changed
Why this level
regraded 2026-09-27 from A: meta-analysis of 10 small trials, GRADE certainty low to very low
Content correction 2026-09-27
Limitations "sauna temp 70-100°C; HWI 40-42°C; duration 15-45 min" -> not in the abstract; removed.
"Works best as an adjunct to active heat exposure ... low-cost maintenance tool" -> not from the paper; relabelled as the base's own practice.
Added n=199 in parser form, the prediction interval, thermoneutral/HR/core-temp/sweat results, and Tier/Sport lines.
Level A -> A- (10 small trials, low to very low certainty).