How to Train for a Heatwave (Economist)

Summary

Pegged to England's World Cup squad decamping to Florida two weeks early and to western Europe's third 2026 heatwave, this Science & technology piece explains the physiology of Heat Acclimatisation and reports that the lab gold standard (controlled hyperthermia in a heat chamber) can be approximated at home — including, per an April 2026 study in over-65s, by hot baths alone.

Key claims (with numbers)

Mechanism — repeated heat exposure raises blood plasma volume, so the heart pumps more per beat and can work at a lower rate for longer; more plasma improves skin blood flow; the body starts sweating at a lower temperature and loses fewer electrolytes in sweat.

Gold standard: controlled hyperthermia — 90 minutes in a heat chamber: 30 min exercise to reach a core temperature of 38.5°C, then an hour alternating exercise and rest to hold it there; daily for 5–7 days; monitored by rectal thermometer. Impractical outside a lab.

Everyday alternatives

1. Exercise outdoors in the heat (Neil Maxwell, environmental physiologist, University of Brighton): "that will naturally acclimatise you."
2. Exercise + hot bath: Scandinavian Journal of Medicine & Science in Sports, 2016 — 40 min treadmill at 18°C followed by 40 min hot bath, daily for six days, improved several acclimatisation measures.
3. Hot bath alone: Healthcare, April 2026, led by Laura Wilson (Middlesex University) — healthy adults over 65, one hour a day in a 40°C bath, showed signs of acclimatisation after four days. Immersion alone raises core temperature enough.

Time course — 75–80% of adaptations build in the first 4–7 days; adaptation is not permanent and decays without continued exposure (Maxwell).

Safety framing in the article — acclimatisation "is not immunity"; Wilson advises replacing 150% of fluid lost in an acclimatisation session and stopping if faint or dizzy.

What is flagged as unproven / not stated

• The 2026 Healthcare study's sample size, design and outcome measures are not given in the article; "signs of acclimatisation" is the article's phrase. Population is narrow (healthy over-65s).
• The 2016 study's n and effect sizes are not reported.
• No study here measures whether home acclimatisation reduces heat illness or mortality in a real heatwave; the outcomes are physiological markers.

Connections

• Heat Acclimatisation — concept page.
• Electrolytes You Probably Don't Need (Economist) — complementary: acclimatised sweat carries fewer electrolytes, which further narrows the case for electrolyte drinks outside intense exertion.
• Minimum Effective Dose of Exercise — a different "how little is enough" question: here, four to seven days of exposure.
• The Economist — Science & technology.

Captured-by trigger

Source file: raw/processed/Economist 2026-07-18 Science---Techn - How to train for a heatwave.md.