The Muscles Targeted By Crunches

Crunches are a common exercise used to develop the muscles in your stomach. When completed on a consistent basis, crunches can improve the strength and tone of the front of your torso, which can improve your posture and prevent back pain. A group of muscles help coordinate the crunch movement.

Crunches

Crunches are completed by lying on your back on the floor. With your feet firmly planted on the floor and knees bent, you crunch up from the abdominals, bringing your head and shoulders up directly toward the ceiling. You can place your hands across your chest, behind your head, or hold them straight up. The exercise is meant to be done in a slow, deliberate manner, not in a jerky movement.

Main Muscles

The main muscles that are recruited to complete the crunch movement are the rectus abdominus and the obliques. The rectus abdominus, which is also referred to as the six-pack muscle, is over your stomach. It originates at the crest of your pubic area and inserts up at your ribs. When it contracts, it tilts your pelvis forward. Your obliques are on either side or your torso. They contract to cause you to flex forward and bend over from side to side.

Hip Flexors

Although not as heavily involved, your hip flexors assist in the crunch movement. Your quadriceps muscle group consists of four muscles, one of which is the rectus femoris. The rectus femoris runs along the front of your thigh and it crosses over your hip joint so that it can assist with bending forward. Along with the main hip flexor muscle, the iliopsoas, the rectus femoris becomes more heavily involved in abdominal exercises that cause you to come all of the way up beyond crunching, such as when completing full situps.

Considerations

To better isolate your rectus abdominus and oblique muscles, complete the crunch movement with your feet up. Placing your feet up on a bench or exercise ball with your knees bent will limit the ability of the rectus femoris to become involved. You can also hold your legs directly up toward the ceiling. According to a 2001 study commissioned by the American Council on Exercise, the vertical leg crunch is among the most effective abdominal exercises for developing your rectus abdominus and obliques.