Muscle Contractions During Crunches

If you want to develop rock hard abs and a clearly defined six-pack, crunches are an ideal exercise to opt for. Of course, unless you lose any excess weight that might be covering those impressive stomach muscles, you won't see the mattress while the duvet is covering it. That said, the way to a lean and defined tummy starts with the contraction of your rectus abdominis muscles -- the abs -- and your obliques -- the waist -- both of which are engaged during a crunch.

  1. Crunch Time

    • You perform a crunch by lying on the floor with your knees bent and feet on the ground, or legs on a bench for support. You place your hands behind your head and pull your upper body toward your knees, bending at the waist, before lowering yourself back to the floor. An exercise mat can be used for comfort and back support.

    A Six-pack to Go

    • The first group of muscles to contract during a crunch are your rectus abdominis. These are the muscles located in your stomach and they control how your lower spine curves and how far you can tilt your pelvis forward. The second group of muscles contracted during a crunch are your obliques, which are located on either side of your waist and upper hips. These muscles allow you to flex and rotate your midsection.

    Resisting the Tension

    • Your muscles contract whenever they come under tension. Tension is caused when your muscles meet resistance that causes them to shorten or lengthen. While you can consciously give your muscles tension by using your body every day, they can also be controlled unconsciously by your central nervous system, which is responsible for controlling muscles such as your heart.

    Slow and Controlled for Best Results

    • There are two phases of muscle contraction. The concentric phase happens first when your muscles start to move. The eccentric phase occurs when your muscle activity starts to slow down. It can be easier to build muscle during the eccentric phase because it’s easier to slowly lower a heavy weight than it is to initially lift one. With that in mind, a crunch can be more effective if you tense your abdominal muscles as you slowly lower your body to the floor during the second half of the exercise after pulling your body toward your knees for the first.