How do I exercise safely in hot weather?

Exercising in heat is not simply uncomfortable. The body cools itself by sending blood to the skin and by sweating, and both compete with the demands of the exercise itself, so the same session genuinely costs more.

Safety

Step by step

1. Understand why it feels harder.Blood is diverted to the skin to shed heat, so less is available to the muscles. Heart rate rises for the same pace. That is physiology rather than a bad day, and pushing through it is the wrong response.
2. Pay attention to humidity, not just temperature.Sweat cools you by evaporating. In high humidity it cannot evaporate, so the cooling mechanism largely stops working. A humid 24°C is harder and more dangerous than a dry 30°C.
3. Move the session earlier or later.Before about ten in the morning or after seven in the evening. The middle of the day in a heatwave is not a training window worth defending.
4. Reduce intensity rather than duration.Go by effort rather than by pace or by the number on a plan. A comfortable conversational pace on a hot day may be a minute per kilometre slower than usual, and that is correct rather than a failure.
5. Drink before you are thirsty.Thirst lags behind fluid loss. Drink through the day rather than only around the session, and take fluid with you for anything over about forty minutes.
6. Replace salt for long or very sweaty sessions.Sweat contains sodium. Beyond an hour of heavy sweating, water alone can dilute what is left — an electrolyte drink, or salty food afterwards, addresses it. This matters more than most people assume.
7. Dress for evaporation.Light, loose, light-coloured, and technical fabric rather than cotton, which holds sweat against the skin. A cap and sunglasses for sun, and sunscreen on everything exposed.
8. Pre-cool if it is very hot.A cool shower, a cold drink, or a wet towel on the neck before starting genuinely lowers core temperature and buys you time before it climbs.
9. Choose the route for shade and water.Shaded paths, a route past a tap or a shop, and loops close to home rather than an out-and-back that commits you to the return. That last one matters most.
10. Let yourself acclimatise.The body adapts to heat over one to two weeks — sweating earlier and losing less salt. The first hot week is the hardest and the riskiest, and it does get easier.
11. Know the warning signs and stop on them.Dizziness, headache, nausea, confusion, cramps, unusually heavy or suddenly absent sweating, or skin that is hot and dry. Stop, get somewhere cool, drink, and cool the skin.
12. Treat confusion as an emergency.Confusion, loss of consciousness, a very high temperature or stopping sweating are signs of heatstroke rather than heat exhaustion. That is 999, not a rest in the shade.
13. Move it indoors or into water.A gym, a pool, or an early swim. Changing what you do for a week is a better answer than doing the usual thing badly and unsafely.

Tips

• Weigh yourself before and after a long hot session occasionally. A significant drop is fluid, and it tells you how much you actually need to replace.
• Dark urine after exercise is the simplest hydration check there is.
• Skipping a session in a heatwave costs almost nothing in fitness. Heat exhaustion costs a week.

Common mistakes

• Holding the usual pace in the heat — The same pace is a higher physiological cost in heat, so you are training harder than intended and much closer to the limit. Go by effort, not by pace.
• Drinking large amounts of plain water after heavy sweating — It dilutes the sodium left after sweating, which in extreme cases is dangerous. Include some salt or an electrolyte drink after long hot sessions.

If it doesn't work

Questions people ask