The weather conditions and pollution problems in Beijing have been frequent topics of controversy surrounding the Olympics. The latest thunderstorms have resulted in the postponement of the rowing, sailing and canoeing with other events also being affected.

However the weather is expected to return to its more usual high levels of heat and humidity. These are difficult conditions to compete in and the heat has caused many of the Olympic competitors to struggle. With the athletics approaching there will be an even bigger emphasis on finding the most effective way to compete in hot conditions.

Sustained hard exercise in a hot environment presents a greater challenge to the body’s homoeostatic mechanisms than any other situation (To read about exercise in other conditions read this all weather training programme). The combination of a high rate of metabolic heat production and a restricted capacity for heat dissipation leads to hyperthermia (high body temperature), which may progress to heat illness, inevitably impairing exercise performance.

When exercising in the heat for the first time, many people experience some of the symptoms of heat illnesses, such as heat cramps, fainting and exhaustion. But the good news is that the occurrence and severity of these symptoms can be significantly reduced by a process of acclimatisation, which allows the body to adapt to the stresses of a warm environment gradually, by repeated exposure.

Complete heat acclimatisation requires up to 14 days of exposure, but adaptations occur at varying rates. Even as few as five days of heat exposure will allow some adaptation to increased environmental temperatures. Within these five days, control of cardiovascular function improves, plasma volume increases, heart rate drops and blood flow is prioritised to reach active muscles and the skin surface. The increase in plasma volume is temporary, allowing the body to cope with the increased need for cooling by redirecting blood to the skin. Taken together, these short-term adaptations lower perception of work rate and allow toleration of the heat prior to longer lasting changes. These changes occur over the next week or so.

Between days five and eight, the body’s thermoregulatory response improves so that sweat rates increase and sweat production starts earlier, so boosting the dissipation of body heat by evaporative cooling. This process prevents body temperature rising critically and also allows for a reduction in skin blood flow as a means of cooling down core temperature, so increasing the blood available to supply active tissues.

(To read about acclimatising to other conditions read this all weather training programme)

By 10 days of heat exposure, sweat rates can be as much as doubled, although individual responses are as varied as individual sweat rates. The early stages of heat acclimatisation see a drop in the loss of sodium chloride (salt) in sweat and urine, resulting in an increased extracellular fluid (ECF) volume. ECF includes the blood plasma, and this process helps the body to maintain a stable core temperature before the later thermoregulatory adaptations occur.

ECF and plasma volume return to normal between days 8 and 14. Following heat acclimatisation, the body has improved efficiency and is better equipped to tolerate the demands of exercise. The heat-acclimatised athlete is able to exercise with a lower skin and core temperature and heart rate than an unacclimatised person. Additionally, muscle glycogen utilisation is reduced and post-exercise lactate concentration is lower.

Although excess fluid and salt intake will not enhance acclimatisation, dehydration or salt deficits will hamper the body’s ability to respond to the heat stimulus, so it is important to maintain an adequate fluid intake during heat acclimatisation. Many studies have shown that dehydration markedly impairs exercise performance and recovery, so it follows that adequate hydration is crucial to a successful adaptation to heat.

If you are gradually acclimatising during a period of warm weather training, around 10 consecutive days of exercise are required, with 2-4 hours of heat exposure each day. The first two days should involve only light exercise lasting about 15-20 minutes, with a gradual build-up of duration and intensity. For optimal acclimatisation, 24-hour exposure to the relevant environmental conditions is better than training in the heat, then resting in an air-conditioned room for the rest of the day. Some high-intensity exercise should be performed in the same heat and humidity as expected for the race, but only after 4-5 days of low-intensity exercise. This protocol combines both passive and active heat exposure to maximise adaptation without causing heat illness.

It is possible to assist the acclimatisation process by exercising in a heat chamber for 1-3 hours per day before departure, but this will be only partially effective and should be seen as an adjunct to, rather than a replacement for, full acclimatisation. Wearing impermeable clothing while exercising may also make a small contribution to the acclimatisation process.

Complete acclimatisation is not always possible for athletes because of the time requirement. And sometimes there is no time at all to acclimatise – such as on those occasions when temperatures suddenly soar. In such cases, you may need to take some short-term measures, such as pre-cooling, to prevent your performance being impaired by the heat. Pre-cooling is a strategy that helps to prevent excessive overheating during exercise by reducing body temperature beforehand.

(For a more detailed consideration of pre-cooling, read this all weather training programme)

Fluid intake plays a vital role in the body’s ability to tolerate heat, and is the most practical intervention strategy for coping with exercise in the heat. Acclimatisation will actually increase fluid needs because of increased sweat rates. By ensuring you replace these lost fluids, plasma volume can be maintained, allowing circulation and sweating to continue and making it easier for you to maintain exercise intensity and duration for longer.

Since carbohydrate conversion to energy is reduced during exercise in the heat, fluid ingestion is geared more to maintaining hydration than to replacing carbohydrate. A large volume of diluted fluid (around 2% carbohydrate) has been shown to be more beneficial in the heat, with increased time to exhaustion for endurance exercise, than no drink or a high carbohydrate (15%) drink. Even plain water is beneficial for maintaining plasma volume, but the addition of a small amount of salt will increase the volume of ingested water that remains in your body, which is especially important when sweat rates and electrolyte losses are high.

A third of a teaspoon of table salt in a litre of water should be enough to improve water retention. Given the large body of evidence relating dehydration to reduced performance during exercise in the heat, fluid replacement should be top of your list of priorities when preparing for warm weather competition.

(For more on hydration read this all weather training programme.)

In conclusion, the successful competitor will have prepared for the heat with a strategy that includes acclimatisation, precooling and hydration. The different elements involved in this process must be carefully planned and fitted to your schedule, with pre-cooling performed in the hours before the competition and hydration maintained throughout your training and race preparation. If practised and followed, these coping strategies should place you well ahead of the pack in terms of your ability to cope with the heat.

To learn how to compete in any condition read this all weather training programme.