In all activities, especially athletic events, the body attempts to maintain a core temperature of 98.6 F. This body temperature is normally controlled by the hypothalamus, which acts as the body’s thermostat. The Winslow Equation is found to be SH=MH +/-R +/-Cd +/-Cv-E. Stated, the Winslow equation is stored heat equals metabolic heat, plus or minus radiation plus or minus conduction, plus or minus convection minus evaporation.
85% of all heat loss occurs through the skin.
To maintain this equilibrium in a hot environment, the body will shunt blood to the periphery where heat is lost through convection and radiation. When air temperature exceeds body temperature, sweating occurs and heat is lost through evaporation, the most effective method of cooling the body. Therefore, the more skin exposed to the air, the cooler the body will be due to the loss of sweat through evaporation. Heat injury is caused when the body loses the ability to sweat.
The body can withstand losing ~1 liter of water per hour for a maximum of 2-4 hours.
However, this tolerance for fluid loss by the body is determined by body size. A 300 lb lineman can withstand losing 2-4 liters of water much more readily than a 100 lb gymnast. When the relative humidity in the surrounding area exceeds 75%, the body is no longer able to lose heat through evaporation. The sweat produced by the body simply stays on the body and is not lost into the air. The result is an increase in body core temperature.
Thermal injury occurs when the body cannot produce enough heat loss to maintain a constant core temperature. Realize that athletes involved in strenuous exercise can have a normal body temperature of 101F. When the body cannot control its core temperature and thermoregulation is lost, the end result is death unless appropriate actions are taken quickly.
The most common type of heat related injury is heat cramps.
These muscle cramps usually occur in the calf of the leg. Core temperature and blood pressure are normal, heart rate is increased, and mentation is normal. Proper treatment includes removal from the heat, removal of tight or restrictive clothing, cooling the body, and relief of the cramp. Prevention of heat cramps can be accomplished through acclimatization, dietary changes, and increased flexibility.
Heat exhaustion is a more serious form of heat illness due to the formation of headaches and possible nausea and vomiting. This vomiting will result in further fluid loss which compounds the heat illness. Additional symptoms include profound sweating, decreased appetite, thirst, fatigue, weak rapid pulse, and cool clammy skin. Effective treatment involves early recognition of the signs and symptoms, removal from the heat source, loosening of the clothing, and cooling of the body. Contact 911 with an emergency call if the patient becomes unconscious or core temperature is greater than 101F.
Heat stroke is a true medical emergency.
Heat stroke signs and symptoms include core temperature in excess of 103F, hot, red, dry skin ( may not be seen in athletes due to perspiration), and a pulse of 160+ initially that decreases with system failure, confusion, anxiety, or psychotic behavior. Treatment involves removal from heat source, removal of all clothing, cooling the body, and an emergency call to 911. Do not forget to evaluate and manage the airway, breathing, and circulation.
Mortality from severe hypothermia can be as high as 87%.
Hypothermia is the generalized cooling of the body due to a decrease in the body’s ability to produce heat. Hypothermia is classified as mild, moderate, and severe. Factors that contribute to hypothermia are perspiration, wind chill, disease, drug use, trauma, and shock. The five general stages of hypothermia are 1) shivering, 2) apathy, 3) decreased consciousness, 4) decreased vital signs, and 5) death. Emergency treatment for hypothermia includes the removal of wet clothing, keeping the victim dry and warm, providing warm, moist oxygen to breathe if available, monitoring vital signs, and handling the victim gently. No hot liquids, massage, or exercise.
Immersion hypothermia occurs when the body’s temperature is suddenly lowered due to immersion in cold water. This immersion can result in cardiac arrest or ventricular fibrillation. Other cold related emergencies can include frostbite, the freezing of body tissues resulting in tissue death. Frostbite is classified in three stages 1) incipient, 2) superficial, and 3) deep.
When it comes to proper hydration – all athletes are different.
Athletes lose fluid at different rates, and therefore, hydration methods and rates will differ. Ideally, a specific rehydration program should be established for each athlete. As a general rule, the athlete should be encouraged and allowed to drink whatever fluid is preferred. However, the athlete should avoid carbonated beverages and “energy drinks.”
The fluid should be easily accessible and small amounts of fluid should be consumed over an extended period of time. Ideally, the athlete should consume 17-20 oz. of fluid 2-3 hours before practice or competition and 7-10 oz 10-20 minutes before practice or competition. This again is directly related to body size and sport.
Encourage athletes to “hydrate until they urinate.” The body will get rid of fluid when the body is properly hydrated. Educate your athletes on monitoring their hydration with a colored urine chart that indicates proper hydration based on urine color.
As a sports medicine professionals, be prepared to recognize signs and symptoms of thermal injury and dehydration. In addition, make a concerted effort in the preseason to educate coaches and especially players on signs and symptoms.