An eccentric contraction is a type of muscle contraction that occurs when the muscle fibers lengthen while under tension, leading to movement. In the context of the abs or back, an eccentric contraction would be the contraction of the muscles that slows down or controls movement away from the center of the body.
For example, during a lowering phase of a crunch, the rectus abdominis (abs) contracts eccentrically to control the descent of the rib cage away from the pelvis. Similarly, in a sit-up, the erector spinae (back) muscles contract eccentrically to control the descent of the upper body away from the legs.
Eccentric contractions play an important role in many exercises, especially those that involve lowering weights or body parts. This type of contraction helps to control the descent, reducing the risk of injury, and providing resistance to build strength. It is important to maintain proper form and control during eccentric contractions to maximize results and avoid injury.