A2

37±0.5 degrees celsius

Increased blood and internal temperature Impulses go to hypothalamus Vasodilation occurs in skin blood vessels so more heat is lost across the skin Sweat glands become more active, increasing evaporative heat loss Body temperature decreases

Conduction, convection, radiation, evaporation

Heat can be conducted through the body’s surface and to the clothing and/or the air (or water) that is in direct contact with the skin. Conduction accounts for less than 2% of heat loss.

Involves moving heat from one place to another by the motion of air (or water) movement. Cyclists gain a cooling effect through convection.

Transfer of energy waves (sun, fireplace, radiator) sent by one object and absorbed by another. The body absorbs radiant heat energy when temperature of the environment is higher than skin temperature.

Conversion of sweat from liquid water to vapor (evaporative cooling). Is the most important avenue for heat loss from the body. As sweat evaporates from the skin, a cooling effect is achieved, thus releasing heat from the body.

Body contains between 2-4 million sweat glands Sweat production depends on density of sweat glands and amount of sweat per gland- back and chest have greatest sweating rates. Sweat glands are located over most of the body and release a solution containing water and minerals through small opening in the skin onto the surface of the body. When this solution evaporates, it effectively cools the skin and regulates body temperature. Sweating during exercise reflects increase in body temp. Also influenced by amount of moisture in air.

Humidity plays a major role in heat loss Affects perception of thermal stress When high (regardless of temperature), limits evaporation of sweat Convection involves moving heat from one place to another by the motion of air (or water) movement. Less wind, less convection, and vice versa.

Wind increases the rate of heat loss (via convection) because the warmer insulating air layer surrounding the body continually exchanges with the cooler ambient air. The wind chill index illustrates the cooling effect of wind on exposed skin leading to a dangerous exposure (frostbite).

Increased vasodilation to assist with cooling Reduced muscle blood flow in high temperatures resulting in increased glycogen breakdown in the muscle and higher levels of muscle and blood lactate in comparison to the same exercise performed in a cooler environment. Reduced blood volume due to excessive sweating. Thus a reduced cooling ability of circulating blood. An increase of body temperature results in a lower venous return (rate of blood flow) to the heart, and a small decrease in blood volume from sweating. A reduction in SV causes the HR to increase to maintain cardiac output. Elevated heart rate (This phenomenon is called Cardiovascular drift)

An increase of body temperature results in a lower venous return to the heart, a small decrease in blood volume from sweating. A reduction in stroke volume causes the heart rate to increase to maintain cardiac output. Include reference to blood viscosity.

Performing training sessions in similar environmental conditions (heat and humidity) for 5 to 10 days results in almost total heat acclimatization. Initially, the intensity of training should be reduced to avoid heat-related problems in these conditions. The total daily exercise-time in the heat should reach 90-100 minutes.

Increased plasma volume Increased sweat response (rate of sweating) Decreased electrolyte content of sweat (thinner sweat) Minerals in body to balance amount of H20 in your body and pH levels Reduced rate of muscle glycogen utilization Decreased heart rate at a given work load and stress Lower core and skin temperature

Heat cramps Heat exhaustion Heat stroke Hyperthermia (a symptom of heat stroke) – core body temperature has risen dangerously high

intense, prolonged exercise in the heat muscle fatigue sodium loss in sweat

pain involuntary spasms of active muscles low serum Na+

stop exercise; rehydrate massage/light stretching

Increasing negative water balance

Fatigue/exhaustion Loss of movement coordination/dizziness Flushed skin Reduced sweating High core temperature

Remove subject to shaded/air-conditioned area Hydrate before and during exercise Acclimatised

Thermoregulatory failure Dehydration

Core temperature >41 degrees celsius Lack of sweating Disorientation/twitching/seizures/coma

Immediate whole body cooling Acclimatise Adapt activities to climatic constraints