Description: Lie supine with knees bent, engage the transversus abdominis with an abdominal compression, and perform a curl up and a pelvic tilt bringing the rib cage and pelvis toward each other. Place your hands behind your head and perform the following movements simultaneously:
1. Pull your hips from the floor using your lower abdominal muscles.
2. Raise your shoulders and back from the floor using your upper abdominal muscles.
3. Move your shoulders toward your hips.
4. Exhale.
5. Hold the contracted position for 1 to 3 seconds.
To increase the effectiveness of the crunch, keep your chest and head lifted and push your lower back flat toward the floor. Avoid collapsing at the chest as you curl up.

Analysis: The crunch is an efficient exercise that combines the muscle action from an abdominal compression, curl up, and pelvic tilt. It works all of the muscles of the abdominal area with a combined movement that is safe and effective.

Muscles worked:
Primary Movers: Rectus Abdominis
Secondary Movers:Transversus Abdominis, Internal Obliques, External Obliques

Variations: This exercise can also be done with your legs placed over a flat exercise bench. Some clients may need to put their legs up to better support and protect the low back.
You can increase the difficulty of the exercise in several ways. Examples include: extending your hands out behind your head, using an incline board, or holding a weight.
See videos: Incline Board Crunch, With Medicine Ball on chest, With medicine ball in outstretched arms, Medicine ball crunch reach