DURING WORKOUT
OBJECTIVE
the same objectives as the preworkout meal apply here (to promote sustained carbohydrate availability & to a lesser degree amino acid availability, minimize muscle catabolism, and spare glygogen) - with the added objective of maximizing water availability & minimizing gastrointestinal upset.
COMPOSITION
again, be aware that we are talking bodybuilding workouts and not triathalon training. i am an advocate of keeping it simple and watering yourself down thoughout the workout with.. you guessed it, pure water. if you did your homework with the right construction & timing of the preworkout meal, there's little need for the bodybuilder to take in much else. now granted, if you were a boxer, triathlete, soccer player, basketball player, or marathoner at risk for catabolizing a good chunk of lean mass and jeopardizing your liver glycogen status by trudging away for far past 90 minutes continuously in an endurance event, definitely sip the gatorade-type 4-8% carb solution throughout the workout, and shoot for 40-60g carbs/hr. there's a huge body of research that shows the benefit of that tactic.
keep in mind that i don't think a during-workout carb solution will hurt the bodybuilder at all, as many mistakenly believe. in fact, a good case can be built for it being an effective nth-degree anticatabolic/anti-hypoglycemic tactic. but all things considered, it just might be unnecessary & expensive, since the energy demands & glycogen depletion of bodybuilders are usually much less. once again, if you had either the right solid meal 60-90 minutes prior, or the right liquid meal 15-30min prior (in a perfect world, BOTH), you technically should still be in the absorption phase. thus you won't experience energy dips seen in fasted-then-fed experimental subjects who obviously benefit from during-workout fuel beyond just water.