Staying Safe When You Exercise in the Heat

When you exercise, your muscles generate heat, and the body has to work to dissipate it. In cooler conditions, this is relatively straightforward. In hot weather, especially when humidity is high, the challenge becomes significantly greater. The body's primary cooling mechanism is sweating, with heat leaving as sweat evaporates from the skin. When the air is hot and humid, evaporation slows and the body has to work harder to stay cool, which puts greater strain on the cardiovascular system and can reduce performance noticeably even before any concerning symptoms appear.

This is a normal physiological response, not a sign that something is wrong. But pushing beyond it without appropriate awareness can move from reduced performance into something more serious.

What happens along the spectrum

Heat cramps are muscle cramps that may occur during or after exercise in the heat, often in heavily used muscles. They're associated with sweating, fluid loss, and electrolyte imbalance. They're uncomfortable but not typically dangerous, and are usually managed with rest, hydration, and taking in some electrolytes.

Heat exhaustion is more significant. It tends to come with heavy sweating, pale and clammy skin, a fast but weak pulse, nausea, headache, dizziness, and fatigue. Someone experiencing heat exhaustion may feel faint or confused. Moving to a cool environment, removing excess clothing, lying down with legs slightly elevated, and drinking cool water are the usual immediate responses. If symptoms don't begin to improve fairly quickly, or if the person is confused, has stopped sweating, or loses consciousness, this may have progressed to heat stroke, which requires emergency medical attention.

Heat stroke is a medical emergency. It involves a high body temperature, often above 40 degrees Celsius, with confusion, altered behaviour, and in some cases loss of consciousness. The body's temperature regulation has essentially failed. This requires calling emergency services immediately while beginning to cool the person down using whatever means are available.

The single most effective strategy in the heat is knowing when to slow down or stop. Performance goals can be adjusted; heat stroke cannot be undone quickly.

Acclimatisation: giving your body time to adjust

One of the most useful things to understand about exercising in the heat is that the body does adapt, given time. With repeated exposure to exercise in warm conditions over about 10 to 14 days, the body makes a number of changes: plasma volume expands, sweat rate increases and becomes more efficient, heart rate at a given effort reduces, and core temperature tends to stay lower. This process is called heat acclimatisation.

Many people arrive at a warm holiday destination and go straight into their usual training intensity, bypassing this window entirely. Scaling effort back for the first week in a new hot environment, and exercising during cooler parts of the day, could make that adaptation period considerably more comfortable.

Hydration and what it actually means

Adequate hydration before, during, and after exercise in the heat matters, but it's easy to overcomplicate. The most useful guide for most people is paying attention to thirst, the colour of urine (pale yellow suggests reasonable hydration), and bodyweight changes before and after exercise. Losing more than about 2 to 3% of body weight through sweat may begin to affect performance and wellbeing.

Plain water is appropriate for most recreational exercise lasting under an hour or so. For longer sessions, or particularly heavy sweating, replacing some electrolytes (especially sodium) alongside fluids may help maintain the balance that regulates fluid distribution in the body. Drinking excessive amounts of plain water without adequate sodium is a less common but real risk, particularly for longer-distance endurance athletes.

Drinks containing caffeine or alcohol before exercise in the heat are worth approaching with some thought, as both can contribute to dehydration.

Practical adjustments for summer training

Timing makes a meaningful difference. Running or cycling in the early morning or evening, when temperatures are lower and direct sun exposure is reduced, could make sessions considerably more manageable. If midday heat is unavoidable, reducing intensity significantly and shortening the duration is sensible. Lightweight, light-coloured, moisture-wicking clothing helps, as does not ignoring shade.

It's worth being a little more attentive to how you're feeling during warm weather exercise, more so than you might be in cooler months. Dizziness, a sudden drop in sweating when you'd expect to be sweating, nausea, or feeling confused or unusually unwell are signals to stop, find shade or cool air, and hydrate calmly rather than pushing on.

Those with cardiovascular conditions, who take certain medications (including some blood pressure and diuretic medications), the very young, and older adults may be more susceptible to heat-related issues, and may find it helpful to discuss summer exercise routines with a GP or practitioner before significantly increasing outdoor activity in warm months.

Summer is genuinely a wonderful time to be active outside, and with a few thoughtful adjustments, most people can continue to enjoy the exercise they love. The heat asks more of your body, and meeting that with a little more awareness, flexibility about timing and intensity, and good hydration could make all the difference.