Le corps humain peut tolérer une variation d'environ 4°C de la température interne du corps sans que les performances physiques et mentales soient affectées. Les joueurs de football, comme c'est le cas dans de nombreux autres sports, sont bien souvent soumis à des conditions climatiques extrèmes. La température externe dans laquelle le match est joué est très importante et aura des effets sur la température interne du corps et donc sur les capacités du jouer.

Le contrôle de la température corporelle dépend d'un équilibre entre la surchauffe et le refroidissement excessif. La température normale du corps se situe à 37°C. Lors d'un match de football, la production de chaleur est augmentée et cet excès doit être éliminé sous peine de voir la performance affectée. La température doit rester comprise entre 37°C et 40°C. La température et l'humidité de l'air externe ainsi que la température du corps peuvent être mesurées précisément grâce à l'utilisation de thermomètres.

La plus grande partie de la température est conduite par la circulation sanguine vers la peau où elle est évacuée de quatre façons différentes :

Conduction: l'excès de température est transféré par contact direct avec un objet (exemple : en nageant dans de l'eau froide).

Convection: l'air en circulation permet à la chaleur d'être transféré à l'air qui passe au contact de la peau (selon la température de l'air).

Radiation: la chaleur est perdue par le corps par radiation (ex. perte de chaleur à l'intérieur d'un environnement froid).

Evaporation: l'excès de chaleur est transférée en transpiration qui s'évapore. La transpiration est le moyen le plus important pour dissiper la température lors d'exercices réalisés dans la chaleur.

Cependant, même avec de grande pertes de chaleur dues à l'évaporation de la transpiration, la température corporelle augmente au cours du match. Toute la chaleur produite ne peut en effet être évacuée. Il a été montré que de part la nature intermittente du football, l'augmentation générale de température est plus élevées que pour un exercice continu. De même, plus l'intensité de l'exercice est élevée, plus la production de chaleur augmente.

Les effets nuisibles de l'exposition au froid sont compensés par l'équilibre entre la production et la perte de chaleur. Il existe une relation étroite entre la performance musculaire et la température musculaire - quand la température décroit, la performance décroit également. Par exemple, la force musculaire est diminuée et le temps de réaction est plus important quand il fait froid. La vaso-constriction, quand le flux sanguin vers les muscles ou les parties extérieures du corps est réduit, a lieu.

Under normal conditions, body fluid loss can be around 2 litres resulting in a negative effect on soccer performance (a loss of only 2% in body mass affects performance). Even in winter conditions, there is still a danger of dehydration if correct fluid replacement is not implemented. Studies under cold conditions have shown that if players do not drink sufficiently, then significant dehydration can still take place.

The risk of injury is also increased when exercising in the cold. Whether this be due to a poor playing surface or incorrect warm-up procedures, athletes should take the necessary precautions. For more information read our article on injury prevention.

To reduce the effects of cold weather, players should be correctly hydrated, undertake a good warm-up session and wear warm appropriate clothing. The coach must play a major part by making sure that players are correctly prepared and checking if the climatic conditions are suitable.

When playing football in hot weather, the heat lost through convection and radiation is minimal thus requiring heat to be dissipated through the evaporation of sweat. In humid conditions the bodies ability to reduce its temperature is further reduced as sweat evaporation is inhibited. The active muscles and the skin are in direct competition for the limited blood supply as the muscles need blood to provide the necessary oxygen and the skin needs blood to facilitate heat loss. Thus, exercising in hot and humid conditions can be dangerous or at least lead to poor performance.

The distances run by players has been shown to be markedly reduced when playing in hot conditions. Evidence also shows that the loss in body water can be more than 3.5 litres (compared to 2 litres in normal conditions). As mentioned earlier a loss of 2% in body mass affects match performance and a 5% loss will decrease the ability to exercise by as much as 30%.

Players can help reduce the effects of a hot climate through:

Fluid intake: adequate fluid intake before, during and after the game/training will avoid dehydration. Players should be correctly rehydrated before competition and take additional drinks when possible. Before exercise, the player's weight should be at it's norm. Drink absorption is at its best when mixed to a weak solution of 2.5 % carbohydrate and rehydration drinks should contain sodium. Thirst is a poor indicator of hydration levels and probably indicates that the player is already dehydrated.

Judging their efforts: Many tournaments are played in hot and humid temperatures which is likely to affect playing performance. Players should try to judge carefully their efforts over the whole match without exhausting themselves from too much high-intensity exercise too soon in the game.

Planning: The coach can judge or measure whether the temperature is too hot for training. Training should not take place in temperatures above 40°C and can be moved to cooler periods (morning/early evening). Plenty of drinks must be made available and exercise intensity levels adjusted accordingly. Training should as well include regular rest periods. Special attention to the conditions must be taken with children when training or playing matches.

Acclimatisation: Players can be acclimatised to hot conditions by spending a defined period of time in the designated place beforehand (10-14 days is recommended as a good adaptation period). However, training sessions should be shorter and easier at the beginning in hot weather. It seems as well that the higher the training level of individuals, the quicker their adaptation to hot conditions with one of the reasons being a greater ability to sweat.

Clothing/Skin Protection: Clothing should be light coloured if possible and made of a lightweight, breathable material so that sweat can evaporate. Football kit soaked in sweat prevents heat loss so should be frequently changed. Sun-block can be used to prevent sunburn.

This article has described the effects of temperature on playing performance. Both the coach and player must take the necessary measures to prevent problems arising when playing soccer in adverse weather conditions. Correct clothing, fluid intake, hydration levels, adaptation, planning and rest periods all play a part in maintaining playing performance. If temperature related illness is suspected, consult a qualified doctor.

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