Crunch (exercise)

The crunch is an abdominal exercise that works the rectus abdominis muscle. It enables both building "six-pack" abs and tightening the belly. Crunches use the exerciser's own body weight to tone muscle and are recommended by some experts, despite negative research results, as a low-cost exercise that can be performed at home. Crunches are less effective than other exercises such as planks and carry risk of back injury.