Proper hydration is required when you have a exercise routine because of the risk of dehydration. The sweat you lose comes from blood plasma. When you lose this blood volume it decreases and you get what is call dehydration. When you dehydrate you lose your capacity to carry oxygen to your blood cells to exercise. When you are going to exercise weight your self first and then at each end the weight you lose is probably all sweat so you may want to get that back by drinking the right amount you lost but you may not want to drink so much because of gain of more weight. Sports drinks are good to hydrate but only if you exercise for a long period of time like a marathon, ironman, or ultramarathon. But if don’t the best choice is to drink water. Because if you exercise for 30 minutes you will not need to replace the minerals that you lose if you were exercising for five hours you would want to drink sports drinks to replace those minerals. You would ask your self so how much of hydration should I drink. At the beginning of your exercise routine drink about 15-20 fl oz this will be 2-3 hours before exercising. During your exercise routine you may want drink 8-10 fl oz every 10 min during exercise but if exercising for more than 90 minutes drink only 8-10 fl oz of a sport drink. then at the end drink 20-24 fl oz for every 1 lb lost.          file:///Users/73304/Desktop/sportsmedicine.about.com:.webloc