Consensus recommendations on training and competing in the heat

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Heat acclimatisation, hydration, and cooling strategies are the key component of safe and better performance during training and competition in the heat.

Summary of the main recommendations for heat acclimatisation

• Athletes planning to compete in hot ambient conditions should heat acclimatise (ie, repeated training in the heat) to obtain biological adaptations lowering physiological strain and improving exercise capacity in the heat.

• Heat acclimatisation sessions should last at least 60 min/day and induce an increase in body core and skin temperatures, as well as stimulate sweating.

• Athletes should train in the same environment as the competition venue, or if not possible, train indoors in a hot room.

• Early adaptations are obtained within the first few days, but the main physiological adaptations are not complete until ∼1 week. Ideally, the heat acclimatisation period should pass 2 weeks in order to maximise all benefits.

Summary of the main recommendations for hydration

• Before training and competition in the heat, athletes should drink 6 mL of fluid per kg of body mass every 2–3 h, in order to start exercise euhydrated.

• During intense prolonged exercise in the heat, body water mass losses should be minimized (without increasing body weight) to reduce physiological strain and help to preserve optimal performance.

• Athletes training in the heat has higher daily sodium (ie, salt) requirements than the general population. Sodium supplementation might also be required during exercise.

• For competitions lasting several days (eg, cycling stage race, tennis/team sports tournament), simple monitoring techniques such as daily morning body mass and urine specific gravity can provide useful insights into the hydration state of the athlete.

• Adequately rehydrating after exercise-heat stress by providing plenty of fluids with meals is essential. If aggressive and rapid replenishment is needed, then consuming fluids and electrolytes to offset 100–150% of body mass losses will allow for adequate rehydration.

• Recovery hydration regimens should include sodium, carbohydrates, and protein.

Summary of the main recommendations for cooling

• Cooling methods include external (eg, application of iced garments, towels, water immersion or fanning) and internal (eg, ingestion of cold fluids or ice-slurry) methods.

• Precooling may benefit sporting activities involving sustained exercise (eg, middle and long-distance running, cycling, tennis and team sports) in warm-hot environments. Internal methods (ie, ice slurry) can be used during exercise, whereas tennis and team sport athletes can also implement mixed cooling methods during breaks.

• Such practice may not be viable for explosive or shorter duration events (eg, sprinting, jumping, throwing) conducted in similar conditions.

• A practical approach in hot-humid environments might be the use of fans and commercially available ice-cooling vests, which can provide effective cooling without impairing muscle temperature. In any case, cooling methods should be tested and individualized during training to minimise disruption to the athlete.

Summary of the main recommendations for event organisers

• The WBGT is an environmental heat stress index and not a representation of human heat strain. It is therefore difficult to establish absolute participation cut-off values across sports for different athletes and we rather recommend implementing preventive countermeasures, or evaluating the specific demands of the sport when preparing extreme heat policies.

• Countermeasures include scheduling the start time of events based on weather patterns, adapting the rules and refereeing to allow extra breaks or longer recovery periods, and developing a medical response protocol and cooling facilities.

• Event organisers should pay particular attention to all ‘at risk’ populations. Given that unacclimatised participants (mainly in mass participation events) are at a higher risk for heat-illness, organisers should properly advise participants of the risk associated with participation, or consider cancelling an event in the case of unexpected or unseasonably hot weather.