1. Heat Loss How heat is lost from the body Evaporation (25%) Radiation (60%) Heat waves Convection to air (12%) Conduction to object (3%) Convection to air (12%) Air currents

2. Balancing heat production with heat loss The circulating blood distributes heat within the body. By varying the quantity of blood circulating just below the skin, the body can control the amount of heat retained or lost to the environment. The body has two mechanisms that operate to either constrict or enhance the dissipation of heat to the environment :Vasoconstriction and Vasodilation.

3. Balancing heat production with heat loss Vasoconstriction Is a decrease in blood vessel size, causing less blood to be supplied to the area that is being serviced by that vessel Is a decrease in blood vessel size, causing less blood to be supplied to the area that is being serviced by that vesselVasodilation Is an increase in blood vessel size, causing more blood to be supplied to the area serviced by that vessel. Is an increase in blood vessel size, causing more blood to be supplied to the area serviced by that vessel.

4. Balancing heat production with heat loss Hypothermia Is a condition characterised by body heat loss that far exceeds body heat gain, resulting in subnormal body temperature. Is a condition characterised by body heat loss that far exceeds body heat gain, resulting in subnormal body temperature.Hyperthermia Is excessively high body temperature which is usually experienced in hot, humid conditions I which evaporation is unable to take place.

5. Vasodilation Increased blood vessel size More blood to that area Vasoconstriction: Decreased blood vessel size Less blood to that area Hyperthermia: Body heat gain exceeds heat loss Condition where high body Temperature is experienced Hypothermia: Body heat loss exceeds heat Gain Causes drop in body temperature

6. Guidelines for fluid replacement Approximately 57% of the total body weight of the average person is water. However, the loss of even a small amount can affect athletic performance. The resting body has the capacity to maintain core body temperature at 37oC, even with an environmental temperature as high as 60oC.However, exercise in the heat can make it difficult for the body to maintain its heat balance, causing the body’s water requirement to greatly increase.

7. Guidelines for fluid replacement The most important cooling mechanism during physical activity is the evaporation of sweat from the body. Sweat is transported to the skin from where it evaporates (water changes into vapour), cooling the body. Environmental warmth and humidity limit the body’s ability to dissipate heat. While high environmental temperatures impede heat dissipation, humidity prevents evaporation.

8. Heat disorder prevention To prevent heat disorder: Hydrate before, during and after physical activity Drink every 15-20 min. while exercising Drink water or low carbohydrate concentration sports drinks Train properly and acclimatise to race conditions.

9. Heat disorder prevention Wear clothing that “breathes” Avoid activity in times of high temperatures and humidity Avoid consecutive days of heavy fluid loss Avoid diuretics, eg. Alcohol Do not exercise if suffering from fever. Learn to recognise symptoms of dehydration.