33.9°C (93°F) Skin Temperature
When air temperature approaches skin temperature your body tries to cool down by sweating. If the conditions are very humid, however, your sweat has more difficulty evaporating - the atmosphere has enough water in it already without taking your sweat as well. So, in humid conditions sweating doesn't cool you down that efficiently.
36.8°C (98.6°F) "Core" Body Temperature
Exercising raises the body's core temperature, but so does hot, sunny weather. In these circumstances your body thermostat will try to cool things down so that your core temperature does not rise to dangerous levels.
38.9°C - 39.4°C (102°F - 103°F) Danger Level
If these cooling processes don't work, the body's core temperature may rise. At this level you will begin to experience heat exhaustion and start to feel some of the following: dizzy, tired, sick, headachy, short of breath, disorientated. If you continue to exercise at this point, you risk raising your core temperature to dangerous levels and you may begin to feel cramping, chills in the trunk and pounding in the head.
40.5°C - 41.1°C (105°F - 106°F) Emergency Level
This is the point at which you risk having heat stroke. The early signs of heat stroke are delirium or loss of consciousness, convulsions and dry skin. Heat stoke is extremely serious and can be fatal. This is an extreme medical emergency: even if you survive, you may suffer permanent brain damage.
The information provided above is for information purposes only and should not be treated as medical, psychiatric, psychological, health care or health management advice. If you have any health or related questions or concerns please contact your medical advisor.
Reproduced by kind permission from the WTA Tour.