Have you ever thought about what some of the top bodybuilders happen to be drinking when they cap off their squeeze bottles between sets and squirt a stream of something into their mouths? Sometimes it's only water, which helps to replace lost water from your system. If you lose too much water during the course of a hard workout without replacing it, you can begin to feel weak.
A second type of drink taken by many bodybuilders is an electrolyte-replacement concoction. The electrolyte minerals (calcium, potassium, sodium and magnesium) can be lost from your system along with water when you sweat heavily in midworkout. As with water, a loss of electrolytes can result in weakness and lack of energy. Usually, most bodybuilders get more than their share of sodium, so most of them supplement with drinks containing only calcium, potassium and magnesium. Some of the more high-tech types will have electrolyte drinks that also contain glucose and extra water, so as to replace virtually everything they’ve lost during a hard workout.
The problem with most electrolyte replacement drinks is that they all taste so raunchy that most bodybuilders would rather drink bat blood. So, my personal solution is to take supplemental electrolyte minerals in tablet form about 30 minutes prior to each training session, then drink either water or a carb-replacement drink during my weight session.
Carbohydrate-replacement drinks are made primarily from glucose polymers, a sugar that's corn-based. In terms of the speed with which it breaks down into something your body can use to provide energy, it's a medium-speed carb about halfway between sugar water and potatoes or rice. Since it takes about 30 minutes for glucose polymers to begin to do their stuff in your bloodstream, start drinking them at least a half hour prior to each gym session, then every 10-15 minutes as you pump iron.