I obtained this information from a physician and thought I'd pass it along.
It takes time to acclimate to warmer weather and it is vital to take in enough fluids so that we don't get into serious trouble.
Unfortunately, every year there are some runners who don't consider all the factors while training or racing and die as a result.
" An individual who is heat acclimated may perspire almost twice as much as an unacclimated individual.
Perspiration and evaporation of perspiration, is the primary means for the body to cool during exercise. Skin blood flow increases significantly during exercise. Blood flowing near the surface results in cooling by both conduction and convection. There appears to be a 25 to 40 percent lower increase in Skin Blood Flow, however, in the older athlete. Sweat glands become active as body core temperature rises. One liter of sweat is generated during the expenditure of about 500 kcal. Studies have shown that training increases both sweating and skin blood flow.
An individual who is heat acclimated may perspire almost twice as much as an unclimatized individual. One of the effects of acclimatization is to allow an individual to begin perspiration earlier in the course of exercise, this allows for a quick, effective and efficient beginning to heat dissipation and alleviation of early heat buildup. Each gram of perspiration that evaporates cools the body by 0.6 kcal. Acclimatized individuals may produce up to 30 g/minute of perspiration. This would allow for considerable cooling.
The environment has a major impact on heat loss. Humidity, playing the largest role, but temperature, of course, also a major factor. These both impact upon heat loss via conduction and convection besides the impact on evaporation of perspiration. The worst possible conditions would be a hot, humid, windless day, following a cool spell.
Heat Induced Illness
Heat Exhaustion
Heat exhaustion is caused by dehydration. The symptoms include chills, light-headedness, dizziness, headache, and nausea. The body temperature is usually between 100 - 102 degrees and profuse sweating is evident.
Treatment should be to get the individual to a cool shaded area and administer fluids either by mouth, if conscious or IV if the individual is unconscious. Seek medical advise.
Heat Stroke
Heat stroke may be fatal
Heat stroke is caused by a sudden failure of the thermoregulatory system of the body. Heat stroke may be fatal. Some consider it to lie on a continuum with heat exhaustion. It initially appears similar to heat exhaustion, but may rapidly progress to manifest more serious neurological symptoms:
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