dehydration

from walking.about.com

The International Marathon Medical Director's Association revised guidelines for drinking and fluid intake for walkers and runners at endurance events in May 2006.

from fitsugar.com

Some people really enjoy working out in the heat under the summer sun. The weather is inspiring as are the other people outside exercising in the heat with you. There is plenty to look at too.

from runnersworld.com

Over the past several years, exercise physiologists have determined that drinking a carbohydrate-protein combo soon after exercise helps speed recovery because it quickly replenishes spent glycogen stores.

To Lower Risk on Jogging Trail, Get Off the Couch - By JANE E. BRODY, New York Times

A previously healthy man in his late 40's died of a heart attack during the Turkey Trot on Long Island last year. Then on Memorial Day, another seemingly healthy man in his 50's went out for a run in Brooklyn and died. When you hear about someone who has suffered a heart attack or sudden cardiac death while jogging, the immediate assumption is likely to be that jogging is dangerous to the heart. But is it? The answer is somewhat paradoxical. While jogging, a person — especially someone with underlying heart disease — is more likely to die than if that person were walking or resting at that same moment.