Most bodybuilders, during resistance training, focus more on pushing the weight up (or pulling it) then the negative portion of the repitition. They let the weight bounce off their chest during bench presses or let the bar swing down during barbell rows. It is important to remember that a greater percentage of microtears occur on the muscle fascia during the negative portion of the repitition. This is because the muscle is stronger and can handle greater weight (leading to more microtears and thus growth) in a concentric to eccentric movement. For optimal muscle gains, control the weight throughout all portions of the repitition, from the negative point as the muscle shifts from concentric contraction to eccentricity. I would also recommend, for maximum muscle fiber recruitment, to focus on squeeze the muscle at the peak of the concentric portion of the movement for 2-5 seconds, and then enter the negative portion of the repititon. If you are not used to this type of slow, deliberate training focusing on muscle fiber recruitment, prepare for lactic acid buildup during the first few weeks. Remember, though, bodybuilding is about discipline and sacrifice and the pain will diminish but the lean muscle will stay.
