"The human body can actually tolerate high temperatures quite well, Minson said. In experiments, people have withstood temperatures as high as 215 F for as long as 30 minutes. And with training, athletes often compete in long-distance running and biking races in desert conditions without dangerously overheating. To cope with rising environmental temperatures, the heart begins to work harder to pump blood to the skin, where blood vessels dilate to allow more heat to dissipate. At the same time, we produce more sweat, which is the body's best strategy for cooling down. In order for sweat to cool us off, though, it has to evaporate. As the salty liquid turns to a gas, the skin gets cooler. That, in turn, cools the blood near the surface of the skin, which then can return to the body's core and protect it from overheating. But with high ambient temperatures and especially high levels of humidity, evaporating beads of perspiration are replaced by pouring rivulets of sweat. The result is a loss of liquid from the blood and the cells, but rivers of sweat do nothing to lower core temperatures." - John (bird whisperer) from Bookmarklet

"People who are in good shape deal better with the heat, because they sweat sooner and more and they have better blood flow to the skin. But even if you're healthy and fit, exercising in the heat can push you over the edge. Experts recommend drinking plenty of fluids and exercising indoors on the hottest days. If you have to get out, drink one to two liters of water per hour. Hit the trails or pound the pavement at the coolest time of day, usually in the early morning. And watch for your area's heat index, which combines temperatures with humidity levels to give a more accurate idea of how your body will respond to the day's conditions." - John (bird whisperer)