Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies (with Périard 2015/16 on cardiovascular adaptations to heat acclimation)
Key Findings
Périard 2021 (Physiological Reviews) — what the abstract covers:
Prolonged exercise in the heat raises core temperature and drains body water via sweat; exercise-heat stress disrupts thermoregulation and fluid balance, leading to hyperthermia, hypohydration, sodium disturbances and, in some cases, exertional heat illness.
Heat stress impairs aerobic performance; hydration status and the systemic and peripheral haemodynamic adjustments contribute to fatigue in the heat.
Mitigation strategies reviewed: heat acclimation, cooling strategies, and hyperhydration.
Methods to measure thermal strain and hydration status are summarised, and contemporary controversies listed.
Périard 2015/16 (Autonomic Neuroscience) — cardiovascular adaptations (full text; not checked against the abstract):
Heat acclimation expands plasma volume, lowers heart rate at a given workload, and improves stroke volume, ventricular filling, skin blood flow and sweating.
Practical Application
Périard's 2021 Physiological Reviews synthesis: prolonged exercise in the heat drives hyperthermia, hypohydration and sodium disturbances that impair aerobic performance through haemodynamic strain, and the main countermeasures are heat acclimation, cooling and hyperhydration — for a hot event, plan acclimation and a cooling and drinking strategy rather than relying on fitness alone.
Limitations
Reviews, not RCTs — strength of individual findings depends on the primary studies aggregated.
The 2015/16 companion is cited without a DOI in this entry; its numbers are not verified here.
Most primary studies are in male cyclists and runners; female and masters athletes are under-represented.
How this entry was checked and changed
Why this level
regraded 2026-09-26 from A: narrative review
Content correction 2026-09-27
"The Critical 48-Hour Rule — degradation begins within 48 h", first-lost sweating vs last-lost plasma volume at 2-4 weeks, and the practical "min 2 heat sessions/week" bullet removed -> none of this is in the 2021 abstract; the plasma-volume ordering also runs against the usual decay literature.
"HR decreases 15-25 bpm", "PV expansion within 3-5 days", "sauna 15-30 min at 80-100 °C" and the overdressing protocol removed -> not verifiable from either abstract; heat-protocol dosing points to SYNTH-04, REF-061, REF-334b.
Level A -> B+ (narrative reviews); Sport "cycling, running" -> general.