Dear Tim
Energy drinks developed for sportsmen and women have a high carbohydrate content and contain some sodium and potassium. If you exercise strenuously you need to replenish your carbohydrate stores in the body and provide instant fuel for your working muscles. Research has shown that athletes who use sports drinks with a high carbohydrate content such as Powerade before, during and immediately after exercise, increase their performance, recover more rapidly and are less prone to developing respiratory infections. The sodium and potassium in these drinks also helps you to hydrate your body more efficiently if you sweat a lot during exercise. Thus you can certainly use such products before, during and immediately after exercise provided that you are really doing strenuous exercise. You would not use such products as "cold drinks" when you are not exercising as they contain carbohydrates with a high glycaemic index and have a very high energy content, because they could make you gain weight if used in excess when you are not expending lots of energy or when you don't need to carbo-load.
Enjoy
DietDoc