REF-561 · Périard, Racinais & Sawka, 2015 · Scandinavian Journal of Medicine & Science in Sports, Vol. · Paper
Heat Acclimation — adaptations and mechanisms (the defining review)
Key Findings (abstract)
Exercise heat acclimation improves thermoregulation, attenuates physiological strain, reduces the risk of serious heat illness, and improves aerobic performance in warm-hot environments — and potentially in temperate environments
Adaptations: better sweating and skin blood flow, lower body temperatures, less cardiovascular strain, better fluid balance, altered metabolism, stronger cellular protection
The magnitude of adaptation depends on the intensity, duration, frequency and number of heat exposures, and on the environmental conditions (dry vs humid heat)
Emerging evidence: controlled-hyperthermia regimens (a target core temperature is maintained) enable more rapid and complete adaptation than traditional constant-work-rate exercise heat acclimation
Acclimating outdoors, in natural field conditions, may give more specific adaptations through direct exposure to the precise environmental and exercise conditions of the competition
Time course (full text; not checked against the abstract): most adaptations develop within ~10-14 days, a large part of them within the first week; they decay over weeks without exposure
Practical Application
Narrative review (Périard, Racinais, Sawka): heat acclimation improves sweating, skin blood flow, body temperatures, cardiovascular strain, fluid balance and cellular protection, cuts heat-illness risk and improves performance in the heat, potentially also in temperate conditions; the dose depends on intensity × duration × frequency × number of exposures and on humidity, and controlled-hyperthermia (target core temperature) protocols adapt faster and more completely than fixed-work protocols.A masters athlete before a hot race should acclimate deliberately, preferably in conditions like the race
Protocol. Not from this paper; the base's own practice: 10-14 daily or near-daily exposures of 60-90 min with core temperature raised (training in the heat, or a sauna/hot bath after a session), finishing close to the race; the abstract supports holding a target core temperature over a fixed work rate
Maintenance: exposures every few days keep the adaptation, which otherwise decays over 2-3 weeks. Not from this paper; the base's own practice
Plasma-volume expansion and the "altitude alternative" logic: the abstract says "reduced cardiovascular strain" and a "potential" temperate-climate benefit — the plasma-volume mechanism is the base's reading (REF-135 for passive heat and VO2max). Inference
Combine with hydration/sodium (REF-007, REF-062)
Limitations
Narrative review; no numbers in the abstract — the time-course and protocol figures are full-text/house values
Individual variability in the rate of adaptation; decay when exposures stop
Transfer to a temperate climate is "potential" in the authors' words
How this entry was checked and changed
Why this level
regraded 2026-09-27 from A: narrative review without systematic method (leading heat-physiology group)
Content correction 2026-09-27
"~10-14 days for full adaptation; partial in 5-7 days", "60-90 min", "every ~5 days", "decays over 2-3 weeks", "plasma-volume expansion" -> not in the abstract; labelled as full text / the base's own practice / inference
Added the abstract's controlled-hyperthermia, dry-vs-humid and field-setting points
Level A -> B+ (narrative review)