Athletes are particularly susceptible to heat-related illnesses because of the relative intensity of their activities. Excessive heat buildup can do tremendous damage to the human body and, in extreme cases, can be fatal.

During exercise, heat produced by the working muscles can increase up to 15 – 20 times that of resting levels. This translates to a 1 degree Celsius increase in core body temperature every five minutes. Under normal conditions, the body's thermoregulatory system maintains a body temperature and an increase in blood flow to working muscles during exercise. There is a concurrent increase in sweating and evaporation to counter this heat production. This so-called "cooling" mechanism continues to work as long as an adequate body fluid volume is maintained by frequent re-hydration. Dehydration causes surface blood vessels to constrict, effectively halting sweat production to conserve blood volume. This leads to a dramatic increase in core temperature, breakdown in the thermoregulatory system, and concurrent increase in body temperature.

Hyperthermia, which is when the body's core temperature begins to rise, occurs in three stages – heat cramps, heat exhaustion, and heat stroke – with the latter being the most serious.

Signs and Symptoms

Heat cramps may be an early sign of heat illness and dehydration. Typically, the athlete complains of cramping in the specific muscles exercised that cannot be relieved with stretching. Cramps can occur after intense, prolonged exercise and result from water loss and imbalances of body electrolytes such as salt, potassium, and calcium. Physical exhaustion and dizziness (especially notable in younger participants) may also be experienced. Poorly acclimatized athletes are more susceptible. It is important to immediately treat the athlete so as to avoid more serious thermal injury.

Heat exhaustion is more serious heat illness and is caused by an excessive loss of body fluids due to prolonged sweating. This condition is characterized by profuse sweating, cool, clammy, and pale skin, and a weak, rapid pulse. The athlete is usually lightheaded, experiences chills or shivering and is unable to concentrate. If left untreated, this can progress to heat stroke, which is a severe, acute life-threatening injury that often results in severe brain damage or death. The distinctions between heat exhaustion and heat stroke are often not so clear cut. It is possible to exhibit signs and symptoms related to heat exhaustion and to have a core temperature indicating heat stroke.

Heat stroke is a medical catastrophe requiring immediate medical attnetion and is characterized by three major symptoms – rectal temperature greater than 40^oC, marked mental confusion and/or unconsciousness, and shock. The individual will likely not be sweating, and their skin will be hot, dry and red. Their pulse will be rapid and bounding and their breathing fast and deep. The most reliable way to diagnose heat stroke, however, is by rectal temperature.

On-Site Management and Treatment

Heat Cramps. This relatively mild condition is a warning to decrease or stop exercise. It is important that the athlete is removed from the heat, re-hydrated with fluids such as water and diluted fruit juices, and monitored for symptoms indicative of a more serious thermal injury. Eating fresh fruit such as a banana will help to replace potassium.

Heat Exhaustion and Heat Stroke. It is essential that the athlete immediately be removed from the heat and placed in a cool area (in the shade or indoors). The death rate from heat stroke is directly related to the length and degree of temperature elevation. If the victim's temperature can be brought down to normal within 45 minutes of its first rise, the risk of death generally does not exceed 10 percent. The victim's clothing should be loosened or removed. Sponging cold water on their body in the presence of a fan will serve to increase the rate of heat loss. The fan should be removed if shivering occurs.

It is also important to take a temperature. The only reliable means of differentiating between heat stroke and heat exhaustion is with the use of a rectal thermometer. Failing that, it is best to "err on the side of caution" and assume the more severe condition. As long as the athlete is conscious, have them drink cool fluids. In cases where the athlete is unconscious, emergency medical attention is required in order for intravenous fluids to be applied. Finally, applying ice packs to major arteries in the neck, groin, and armpit regions and placing cold, water soaked sheets, towels, or clothing over the athlete will facilitate cooling of the blood from the skin returning to the heart.

Associated Risk Factors

Each individual athlete has a specific tolerance to heat exposure that may vary depending on general health, bosy size (surface area and body ratio), level of fitness, acclimatization, state of exhaustion, recent diet, as well as liquid and electrolyte consumption. As well, individuals who are younger than 15 and older than 40 are more susceptible to the heat.

Athletes should have unrestricted access to water at all practices and competitions. They should be encouraged to drink more water than they may want, especially during periods of extended activity in warm weather. Water loss can be compensated for by adequate water intake before, during, and after the exercise period. Diluted commercial electrolyte drinks can also be used, however, at full strength both these and salt tablets will decrease the absorption rate of badly needed water. Note that salt tablets are not recommended as they sit in the stomach and do more harm than good. Often athletes can prepare for the increase of electrolyte loss during intense activity in heat by adding small amounts of salt to their regular diet prior to competition.  Unless a sufficient amount of body surface area is exposed, sweat cannot evaporate and the body will not cool. Both the athlete's equipment and clothing should allow for adequate evaporation of sweat during periods of high temperature and humidity, and should not excessively cover heat loss areas (neck, underarms, inner thigh).

Practices and games should be scheduled so that the athletes are not exposed to peak daytime temperatures. It is wise to use the National Weather Service's heat index. A 4-8 day program of progressively longer periods of exercise in the heat improves the circulatory and sweating responses that dissipate heat, thus minimizing the incidence of heat exhaustion. Training should increase slowly (i.e. over a 2-3 week period) in climates of higher temperatures and/or humidity than that which the athletes are accustomed. Younger athletes, poorly conditioned athletes and overweight athletes take longer to acclimatize.

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McArdle, W. D et al. (1991). Exercise Physiology: Energy, Nutrition and Human Performance (third ed.). Malvern, PA: Lea and Febiger.