Heat stroke is the most serious of the three progressive forms of heat-related injury. Heat stroke is an insidious condition, as it commonly reaches an irreversibly fatal level by the time first aid or emergency measures are available. Heat stroke is a leading global cause of preventable death, in both athletic and non-athletic circumstances.
The heat-related injuries of heat cramps, heat exhaustion, and heat stroke are progressive in nature, in the sense that muscle cramps is the least serious, heat stroke is the most serious, and each injury has common factors in causation, formation, and treatment. Heat stroke can, however, arise without the person necessarily moving through all of the symptoms of the lesser two conditions. When the circumstances are present, heat stroke can present itself without other symptoms.
Heat stroke represents a wholesale failure of the human thermoregulatory system, whereas the symptoms of heat exhaustion and muscle cramping caused by heat cramps might be equated to thermoregulatory equipment breakdowns. Heat stroke is caused in one of two situations: when the body is unable to cool itself due to extreme environmental conditions, or when the body produces excessive amounts of heat.
In the normal function of the body, heat may be dissipated in four separate ways. Conduction is the ability of the body to transfer heat by direct contact with a cooler object. Conduction will account for approximately 2% of heat loss. Convection is the process where body heat is transferred to the air surrounding the body. The humidity of the immediate environment will have an impact on the ability of the air to absorb body heat. If the body temperature is 100°F (38°C), and the surrounding, or ambient, temperature is 105°F (41°C), the body will absorb warmth from the air, and it will not transfer heat. Convection will account for 10% of the heat dissipated by the body in normal circumstances. Radiation is the process where body heat is transferred to the surrounding environment by electromagnetic waves. As with convection, so long as the ambient temperature of the air is less than that of the body, heat will be transferred away from the body. Approximately 65% of the excess body heat is transferred by radiation. Evaporation is the heat transfer process in which liquid perspiration produced on the skin is released into a vapor. In normal circumstances, approximately 30% of the heat from the body is released in this fashion.
The losses of fluid from the body during exertion in hot weather are remarkable in proportion to the size of the body. A 200 lb (98 kg) person exercising at a moderate level in 90°F (32°) temperatures will lose between 30 and 60 oz (1-2 l) of body fluids during every hour of exercise. If the fluids are not properly replaced, the body's initial protective response mechanism to conserve valuable fluid is to reduce its core temperature. This is achieved through restricting the flow of blood to the peripheral parts of the body, particularly the limbs. Ultimately, the body does not have a mechanism with which to carry away the heat, a process that results in a reduced flow of blood to the brain and central nervous system impairment. If unchecked, and body temperatures continue to rise, there will be clear physical impairment of the person, including dizziness, nausea, and an inability to speak coherently. Organ failure and death are inevitable results of untreated heat stroke.
Sports that present the greatest risk of heat stroke are those played out of doors in warm weather conditions. Soccer, rugby, American football, and distance running are particular examples, as each combines the necessary environment with an activity that places significant stresses on the capabilities of the body, in addition to the dissipation of heat. Cycling can also contribute to the creation of heat stroke, but as the speed of the bicycle creates convection, cycling presents a lesser risk that the field sports.
Medical attention for the athlete that has sustained heat stroke is essential. The preliminary actions will include the immediate removal of the athlete to a cooler environment. Often the administration of intravenous fluids will be required. A gentle lowering of the core temperature of the athlete, combined with the consumption of fluids, is the early objective of treatment. Immersing the athlete in cold water or ice bath is a shocking event for the body in these circumstances and is dangerous. It may take 24 hours or longer to restore the fluid levels of the injured person. The athlete should be restricted from any form of training for a period ranging from four to seven days.
The physical and the neurological function of the athlete should be assessed as a consequence of this serious heat injury, given the risk of both muscle and organ tissue damage.