Crunch (exercise)

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The crunch, often mistaken for a curl-up, is one of the most common exercises for the abdominal muscles, primarily the rectus abdominis. 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, as this can cause injury. Alternatively, the hands may be placed on the shoulders, with the forearms crossed over the chest.

Crunch exercises may be performed on swiss balls. Weights may be used, typically held under the chin, to increase resistance.

Unlike the sit-up, the lower back should not leave the floor. This is said to eliminate any involvement by the hip flexors, and make the crunch an effective isolation exercise for the abdominals. The difficulty of the crunch can be increased by lying on a decline bench and/or holding a weight on the chest. Alternatively, a crunch machine may be used.

Critics of the crunch have pointed out that the hip flexors are not in fact eliminated from the movement by the lower back being kept on the ground. Tension spreads from the abdominals to the hip flexors, and the tension of the hip flexors reduces the workload on the rectus abdominis.

Variants include:

• The reverse crunch is performed by curling the legs and 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.