Endurance sporting activities such as Football, rugby or netball, amongst others are frequently played in hot and humid conditions. In some situations, especially when there is also high humidity, players may develop heat illness. During exercise, the body core temperature rises and may exceed 40°C. Heat is produced from endogenous sources, such as muscle activity and metabolism, and exogenous sources, where heat is transferred to the body when environmental temperature exceeds body temperature.
When the environmental temperature equals or exceeds the body temperature, evaporation is the predominant mechanism of heat loss, providing approximately 90% of the heat loss capacity. In hot temperatures, an increasing fraction of cardiac output is directed to the skin (in an attempt to cool the player), thereby limiting performance. In football, the intermittent character of the effort (short bouts of sprinting and running in between periods of walking) limits energy expenditure and allows players to adjust their speed according to the thermal load.
However, professional and elite players are more athletic. They may push themselves harder than recreational players and may be more at risk of developing heat illness, however the latter are also at risk playing in such conditions. Playing in an enclosed stadium may also impose an increased risk as the playing field is shielded from wind, the stadium walls may reflect radiation and there is additional thermal radiation from heated walls. In professional settings, objective measurements are usually done by the aid of a wet bulb globe thermometer (WBGT) as the best measurement of heat stress. In its absence ambient temperature may be used to guide assessment of heat illness risk during sporting activity. The risk is proportional with temperature rise:
Ambient temperature in relation to risk (applicable to our setting): 25-31.9 degrees Celsius: moderate 32-38 degrees Celsius: High >38 degrees Celsius: Extreme PREVENTION OF HEAT ILLNESS IN FOOTBALL As with the medical conditions related to the environmental stressors, prevention is possible and is a key consideration. Mandatory cooling breaks were established in various sporting codes and are key to prevent the development of heat-related illness in players and/or referees on the field of play. Broadly speaking, the prevention of heat illness can be achieved through five key areas.
1. Avoid adverse times of day for training or matches: Where possible, matches should be scheduled for cooler times of the day. Playing in hot conditions both increases the risk of heat illness and impairs performance. Event organizers should attempt to organize matches at a time where less heat stress and exposure is expected. They should reschedule matches where the heat stress is extreme.
2. Wearing appropriate clothing: Lightweight, breathable clothing is needed when training and playing in hot conditions. This type of clothing allows evaporative cooling to occur (evaporation of sweat). Heavier items of clothing can limit heat loss through this source. NB: Do not use black plastics as undergarments for the purpose of weight loss or endurance gain during these hot conditions.
3. Appropriate hydration: Ensuring that players are hydrated is an important strategy. Water breaks in the 30th and 75th minute of the game are mandated during ambient temperatures more than 38°C (in practicality at intervals of each playing half). It is, however, essential to recognize that even well-hydrated players can be affected by heat illness. With respect to hydration, dehydration of at least ~2% body mass is needed to impair aerobic performance in warm-hot conditions. Practical strategies that can be used to monitor hydration include the color of a player’s urine and measuring pre- and post-exercise body weights. These can be good educational strategies for players and can reinforce the need to pay more attention to hydration.
4. Avoid medication putting athletes at risk: The use of some medications can increase the chance of developing heat illness. The use of caffeine supplementation prior to a game, common among many elite players, can increase the risk of problems. Other medications which may predispose to heat illness include phenylephrine (in cold and flu tablets), antihistamines, some antihypertensives, tricyclic antidepressants, thyroxine and benzodiazepines.
In general terms, players should be advised to minimize the use of all medication (where possible). The use of alcohol can also predispose to thermal illness. 5. Acclimatization: This is an issue for teams travelling to a hot environment. Where possible, a team should arrive well in advance of competitive matches. This allows acclimatization to occur and can be a very effective way of both preventing heat illness and thereby enhancing performance.
After travelling to a hot climate, athletes adapt, leading to an increased plasma volume and venous tone and alterations in the sweating mechanism. These sweating changes include earlier onset of sweating, an increased amount of sweating, and an increased dilution of the sweat. This means that the sweat has a lower sodium concentration. All of these changes allow an athlete to perform better in a hot environment. The minimum time required for heat acclimatization for aerobic performance is probably two weeks.
However, within six to ten days, significant adaptations can occur and adaptations occur more rapidly in highly trained athletes. It is usually recommended to live and train in hot conditions for at least 60 minutes per day throughout this time but adaptations have been shown with shorter durations of heat exposure.
The adaptive responses are individualized and appear to vary significantly across footballers. The benefits of acclimatization are lost more slowly than they are gained – usually over two to four weeks. Heat acclimatization may also have some benefit as a training stimulus leading to improved performance in a temperate environment. In all aspects prevention as outlined above remains key in our setting where we don't have capacity for immediate medical support in the event of heat related illness or emergencies in sports which we will focus on in the next edition.
When the environmental temperature equals or exceeds the body temperature, evaporation is the predominant mechanism of heat loss, providing approximately 90% of the heat loss capacity. In hot temperatures, an increasing fraction of cardiac output is directed to the skin (in an attempt to cool the player), thereby limiting performance. In football, the intermittent character of the effort (short bouts of sprinting and running in between periods of walking) limits energy expenditure and allows players to adjust their speed according to the thermal load.
However, professional and elite players are more athletic. They may push themselves harder than recreational players and may be more at risk of developing heat illness, however the latter are also at risk playing in such conditions. Playing in an enclosed stadium may also impose an increased risk as the playing field is shielded from wind, the stadium walls may reflect radiation and there is additional thermal radiation from heated walls. In professional settings, objective measurements are usually done by the aid of a wet bulb globe thermometer (WBGT) as the best measurement of heat stress. In its absence ambient temperature may be used to guide assessment of heat illness risk during sporting activity. The risk is proportional with temperature rise:
Ambient temperature in relation to risk (applicable to our setting): 25-31.9 degrees Celsius: moderate 32-38 degrees Celsius: High >38 degrees Celsius: Extreme PREVENTION OF HEAT ILLNESS IN FOOTBALL As with the medical conditions related to the environmental stressors, prevention is possible and is a key consideration. Mandatory cooling breaks were established in various sporting codes and are key to prevent the development of heat-related illness in players and/or referees on the field of play. Broadly speaking, the prevention of heat illness can be achieved through five key areas.
1. Avoid adverse times of day for training or matches: Where possible, matches should be scheduled for cooler times of the day. Playing in hot conditions both increases the risk of heat illness and impairs performance. Event organizers should attempt to organize matches at a time where less heat stress and exposure is expected. They should reschedule matches where the heat stress is extreme.
2. Wearing appropriate clothing: Lightweight, breathable clothing is needed when training and playing in hot conditions. This type of clothing allows evaporative cooling to occur (evaporation of sweat). Heavier items of clothing can limit heat loss through this source. NB: Do not use black plastics as undergarments for the purpose of weight loss or endurance gain during these hot conditions.
3. Appropriate hydration: Ensuring that players are hydrated is an important strategy. Water breaks in the 30th and 75th minute of the game are mandated during ambient temperatures more than 38°C (in practicality at intervals of each playing half). It is, however, essential to recognize that even well-hydrated players can be affected by heat illness. With respect to hydration, dehydration of at least ~2% body mass is needed to impair aerobic performance in warm-hot conditions. Practical strategies that can be used to monitor hydration include the color of a player’s urine and measuring pre- and post-exercise body weights. These can be good educational strategies for players and can reinforce the need to pay more attention to hydration.
4. Avoid medication putting athletes at risk: The use of some medications can increase the chance of developing heat illness. The use of caffeine supplementation prior to a game, common among many elite players, can increase the risk of problems. Other medications which may predispose to heat illness include phenylephrine (in cold and flu tablets), antihistamines, some antihypertensives, tricyclic antidepressants, thyroxine and benzodiazepines.
In general terms, players should be advised to minimize the use of all medication (where possible). The use of alcohol can also predispose to thermal illness. 5. Acclimatization: This is an issue for teams travelling to a hot environment. Where possible, a team should arrive well in advance of competitive matches. This allows acclimatization to occur and can be a very effective way of both preventing heat illness and thereby enhancing performance.
After travelling to a hot climate, athletes adapt, leading to an increased plasma volume and venous tone and alterations in the sweating mechanism. These sweating changes include earlier onset of sweating, an increased amount of sweating, and an increased dilution of the sweat. This means that the sweat has a lower sodium concentration. All of these changes allow an athlete to perform better in a hot environment. The minimum time required for heat acclimatization for aerobic performance is probably two weeks.
However, within six to ten days, significant adaptations can occur and adaptations occur more rapidly in highly trained athletes. It is usually recommended to live and train in hot conditions for at least 60 minutes per day throughout this time but adaptations have been shown with shorter durations of heat exposure.
The adaptive responses are individualized and appear to vary significantly across footballers. The benefits of acclimatization are lost more slowly than they are gained – usually over two to four weeks. Heat acclimatization may also have some benefit as a training stimulus leading to improved performance in a temperate environment. In all aspects prevention as outlined above remains key in our setting where we don't have capacity for immediate medical support in the event of heat related illness or emergencies in sports which we will focus on in the next edition.
