The crunch is the most common strength training exercise for the abdominal muscles. It is performed while lying face up on the floor with knees bent, by curling the shoulders up towards the pelvis. The hands may be placed behind the head, but care should be taken not to pull on the neck. Alternatively, the hands may be placed on the shoulders, with the forearms crossed over the chest.
Unlike the sit-up, the lower back should not leave the floor. This eliminates any involvement by the hip flexors, and makes the crunch an effective isolation exercise for the abdominals. Advanced practitioners often increase the difficulty of the crunch by lying on a decline bench and/or holding a dumbbell on their chest. Alternatively, a crunch machine may be used instead.
Variants include:
- The reverse crunch is performed by curling the pelvis towards the shoulders. More emphasis is placed on the lower abdominals.
- The twisting crunch is performed by lifting one shoulder at a time. More emphasis is placed on the obliques.
- The cable crunch is performed while kneeling upright by curling the body to pull down on a cable machine. The hips should be kept motionless, so that the individual's bodyweight does not assist the movement.
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