Ab Crunch Machine

The (ab) crunch is one of the best-known exercises for the abdominal muscles. The rectus abdominis (the basis of the “six-pack”) pulls the sternum toward the pelvis by rounding the back. The transverse abdominis (beneath the obliques) pulls the abdominal wall inward and thus acts as a natural weightlifting belt to stabilize the core.

Performing the crunch on a machine makes it possible to use higher resistance.

Some crunch machines have a pad that is placed against the chest. Others have a contact point for the upper arms (example photo).

Crunch Machine execution

1
Bring your chest toward your waist by rounding your back. Focus on pushing your chest forward and downward, rather than on your arms (which merely follow the movement).
2
Straighten your back again to return to the starting position.

Crunch Machine

Active muscles:

Rectus abdominis
External oblique
Internal oblique
Transversus abdominis (corset muscle)
Rectus femoris

Crunch Machine setup

Adjust the height of the seat pad so that the pivot point is just below the chest.
Place your upper arms on the arm pads. Depending on the machine, you can place your forearms in line with them, or there may be a separate contact point for the hands. This is your starting position.

Crunch Machine technique

Regular crunches use part of your body weight as resistance. Performing the exercise on a machine can provide higher resistance. This is useful, for example, if you can do dozens of crunches while muscular endurance is not your goal.

During a regular crunch, the obliques on the sides stabilize the core by resisting lateral tilting and rotation. When performed on a machine, they do not need to work as hard to stabilize.

When training the abdominals, muscles in the pelvis and upper legs are often also engaged unconsciously. These include thigh muscles such as the rectus femoris and sartorius, as well as shorter muscles in the pelvis. Performing the exercise on a machine makes it more difficult to bend from the hips and therefore reduces the likelihood of excessive involvement of muscles other than the abdominal muscles.