Heat related illness and exercise

Keeping a constant body temperature of around 37 °C is vital. To lose heat and maintain core temperature, blood vessels in the skin expand and bring body heat to the skin surface. Perspiration floods out of sweat glands and evaporates from the skin to cool the body.

Heat stress

At rest and in comfortable temperatures, a person sweats about 2 litres of fluid every 24 hours. During hot weather (35 °C and above), this fluid loss can leap to around 10 litres over the same time period. Exercising in hot weather accelerates fluid loss even more.

Heat stress occurs when sweat can’t evaporate fast enough to keep the body sufficiently cool. Many of the symptoms occur as a result of excessive loss of body salts and water (dehydration).

Symptoms of heat stress

The symptoms of heat stress include:

• deterioration in sporting performance
• muscle cramps
• headache
• dizziness
• nausea
• vomiting.

If the symptoms are ignored and left untreated, it can lead to a life-threatening complication known as heatstroke.

Children and the elderly are particularly vulnerable to dehydration and heat stress.

How to prevent heat stress during exercise

Suggestions to prevent heat stress during exercise include:

• Fitness – a physically fit body is better able to manage the stresses of sport.
• Acclimatisation – keep up an exercise program during the cooler months, so that your body is prepared for sport during summer.
• Avoid the hottest part of the day – start sporting activities before 9 am or after 6 pm during summer, and try to avoid sport or exercise during the hottest part of the day.
• Clothing – wear loose, light-coloured and comfortable clothes made from natural fibres such as cotton. Wear a visor or hat.
• Stay hydrated – as a general rule drink at least half a litre of fluids in the 2 hours before exercising. During your exercise, aim to drink about 200 ml every 20 minutes or so. Choose a specially formulated sports drink if your sporting event goes for more than an hour. After exercise, drink around half a litre of water.
• Alcohol – alcohol dehydrates the body, so avoid drinking any alcohol for at least one day before playing sport.
• Rest breaks – frequent breaks in the shade allow the body to cool down.
• Check for symptoms – be alert for the symptoms of heat stress or dehydration.

Calculating your fluid requirement

To work out how much water on average you need to drink, weigh yourself before and after exercise. A loss of one kilogram equals a loss of one litre of fluids. If you find you have lost weight after exercise, try to increase your fluid intake next time.

Managing heat stress

Suggestions to treat heat stress include:

• Rest in a cool, shaded place.
• Remove excess clothing.
• Drink plenty of liquids, either cool water or diluted sports drink.
• Sponge the body with tepid water and fan to promote sweat evaporation.
• Don’t douse the body with cold water or ice, as this will encourage the blood vessels in the skin to constrict and retain body heat.
• Seek medical assistance.
• If the person is confused, unconscious or has trouble breathing, call an ambulance immediately.

Where to get help

• In an emergency, always call triple zero (000)
• Your GP (doctor)
• NURSE-ON-CALL (24 hours, 7 days) Tel. 1300 606 024 – for expert health information and advice