Basically, there are two phases to every resistance training exercise.
First, there is the concentric phase of a muscle contraction, which involves the shortening of a muscle. It’s when your chest and shoulder muscles contract when you push up into a pushup, or how your biceps flex during a biceps curl.
But there is also the eccentric phase, which is the lowering – or negative – portion of the lift. That’s when you lower yourself back toward the ground during the pushup, lengthening the chest and shoulder muscles. Or when you lower the weight during the biceps curl, elongating your biceps muscles.
People usually pay more attention to the concentric contraction. You can see this in just about any gym as people lift weights up in a very controlled manner, then let them sort of flop back down to the starting position before lifting them up again.
Controlling the negative phase deserves more attention.
Because while concentric training definitely has benefits, you actually develop more strength and growth during the eccentric phase.