As dehydration progresses cooling becomes more difficult. Performance drops and heat injury becomes a real threat. Often the border between them is blurred into a continuous spectrum. Heat cramps are due to muscle spasms and often occur in the arms, legs, or abdomen. They are thought to be caused by dehydration and loss of salt and other electrolytes.
Heat exhaustion is due to more profound loss of water and electrolytes.
Both can usually be treated by moving out of the sun, drinking fluids, and eating salty food. Heatstroke is a life threatening condition and represents severe dehydration, high body temperature, and a shut-down of the cooling mechanisms. The athlete may be delirious or comatose, and half of the victims have stopped sweating. The oral temperature is notoriously inaccurate in these circumstances. Damage to the brain, heart, lungs, kidneys and other organs may occur.