The crunch is an exercise that is performed by lying flat with the knees bent and the feet flat on the floor, and using the abdominal muscles to lift the shoulders and head toward the lower portion of the body without lifting the lower back. Crunches differ from sit-ups because the lower back is kept in contact with the surface on which the exercise is performed. A bench crunch uses a special bench, usually decline or vertical, to increase the difficulty of the ab crunch exercise. Benches generally include extended pads to hold the feet and legs in place to insure the effectiveness of the exercise. Sometimes a bench crunch is performed using weights, either a weight plate or dumbbell, to further increase its difficulty.
The name crunch originates in the crunching of the stomach that results from lifting the head and shoulders with the abdominal muscles. Crunches are ordinarily done with the hands either locked behind the head or with the arms crossing on top of the torso so that the hands lie flat on the upper portion of the chest on the opposite side. To perform a crunch properly, the arms should not assist in lifting the head and shoulders.
Either position, hands behind head or arms across chest, is effective to use in a bench crunch. To perform a bench crunch, begin with a decline bench. The steeper the decline the more difficult the crunch, so beginners should make sure to use a bench with a lesser decline. Only those with advanced fitness proficiency should opt for a vertical bench due to the difficulty involved in its use. Lie flat on the bench and lock the feet behind the provided pads, with the front of the foot held tight against the pads, and follow the same procedure as in an ordinary ab crunch.
If bench crunches are not challenging enough, holding a weight plate on the chest provides additional resistance and increases the intensity of the ab workout. A dumbbell may also be held against the chest or, for advanced exercisers, above the head instead of a weight plate. While crunches are an effective exercise for strengthening the abdominal muscles, the crunching motion is potentially bad for the back. If back pain occurs while performing crunches or previous back pain is an issue, an alternative abdominal exercise should be sought that does not involve a bending motion.