Positive and Negative Phases of Weightlifting
Talk in a weight room among experienced lifters may revolve around “doing negatives.” This doesn’t mean they’re going to stop exercising and go for a snack. “Doing negatives” refers to a particular way to perform an exercise. It’s weight room jargon, but it’s also talking biomechanics.
Positive work is performed when a force is applied to a body, and the body moves in the direction of the applied force. Negative work is performed when a force is applied to a body, but the body moves opposite to the direction of the applied force.
When lifting weights, each rep consists of a positive and a negative phase of work performed by the lifter on the bar. Consider the bench press, an exercise where the lifter lies on her back holding a bar in her hands and alternately lowers it and raises it above her chest (a complete rep consists of a lowering phase and a raising phase). While lowering the bar to her chest, the lifter pushes up on the bar and the bar moves down. The lifter does negative work on the bar. While raising the bar above her chest, the lifter pushes up on the bar and the bar moves up. The lifter does positive work on the bar.
Muscles are producing force eccentrically while the bar is lowering. The same muscles produce force concentrically while the bar is rising. Muscle can produce more force when it’s active eccentrically than it can while active concentrically. Practically, this means that you can lower more weight than you can lift.
“Doing negatives” in the weight room refers to completing sets of just the lowering phase of a lift, using a heavier bar than what can be used through a complete rep of down and up. A partner assists the lifter to raise the bar back up.