How to exercise safely in a heatwave: what health experts advise

When a heatwave settles over a country, the instinct for many active people is to carry on as normal, lacing up for the usual run or heading to an outdoor training session. Health officials have a blunt warning: even the young and fit should ease off, skipping strenuous exercise and cutting back on alcohol when temperatures spike, because being in good shape offers no guarantee of safety in extreme heat.

The reasoning lies in how the body copes with heat. Exercise generates internal warmth that the body must shed, mainly by sweating and by sending blood to the skin. On a hot, humid day that cooling system is already under strain, and hard exertion can push core temperature to dangerous levels faster than people expect, regardless of their fitness.

That is why officials stress that youth and athletic conditioning are not shields. Fit people can often push themselves harder, which paradoxically raises the risk, because they may override the early signals that tell a less-trained person to stop. Heat illness can strike marathon runners and amateur cyclists as readily as anyone else.

The spectrum of heat illness runs from mild to life-threatening. Heat exhaustion brings heavy sweating, dizziness, nausea, headache and a rapid pulse, and is a signal to stop, cool down and rehydrate. Heatstroke is the medical emergency at the far end: the body's temperature regulation fails, the skin may become hot and dry, and confusion or collapse can follow. It requires urgent medical help.

Alcohol makes all of this worse, which is why the advice pairs skipping runs with going easy on drink. Alcohol is a diuretic that promotes fluid loss and can mask the early symptoms of dehydration and overheating, leaving people less aware that their body is struggling just when awareness matters most.

None of this means abandoning activity altogether. The practical guidance is about timing and intensity. Exercising in the cooler early morning or later evening, rather than the midday peak, sharply reduces the heat load, as does moving a workout indoors to an air-conditioned space or swapping a run for a swim.

Hydration is the other pillar. Experts advise drinking water before, during and after activity rather than waiting until thirst sets in, since thirst lags behind actual fluid needs. For longer or sweatier sessions, replacing salts lost in sweat can matter too, though for most people plain water and a balanced diet are enough.

Clothing and preparation help as well. Light, loose, breathable fabrics, a hat, sunscreen and shade all reduce strain, and slowing the pace or shortening the session lets the body cope with conditions it is not acclimatised to. Acclimatisation itself takes time, which is why the first hot days of a heatwave are often the most dangerous.

Certain groups need extra caution. Older adults, young children, pregnant women and people with heart or lung conditions are more vulnerable, but the current warnings are notable precisely because they extend the caution to healthy young adults who might assume the advice is not aimed at them.

The overarching message from health authorities is one of proportion, not fear. Staying active is good for health, but during extreme heat the safest approach is to adapt, moving sessions to cooler hours, dialling down the intensity, drinking enough and heeding the body's warning signs, so that a summer workout does not turn into a medical emergency.