Lying Crunch on Stability Ball
The (abdominal) crunch is one of the best-known exercises for the abdominal muscles. The rectus abdominis (the basis of a 'six-pack') draws the sternum toward the pelvis by rounding the back.
The oblique abdominal muscles at the sides stabilize the core by preventing lateral flexion and rotation. The transversus abdominis (beneath the oblique abdominal muscles) draws the abdominal wall inward and thereby acts as a natural weightlifting belt to stabilize the core. When performed on a stability ball, these muscles may have to work harder. The muscles in the legs and glutes will also have to work harder to stabilize the body.
Crunch (on stability ball)
Active muscles:
- Rectus abdominis
- Obliquus externus abdominis (external oblique)
- Obliquus internus abdominis (internal oblique)
- Musculus transversus abdominis (transversus abdominis, or 'corset muscle')
Execution:
- Lie with your back on the stability ball. Make sure the ball is positioned in the natural curve of your back.
- Place your feet flat on the floor.
- Cross your forearms over your chest.
- Straighten your back and then round it by bringing your chest toward your pelvis.
- Hold the tension for 1 to 2 seconds.
- Slowly bring your chest back and down.
Crunch (on stability ball) execution
Besides the stabilizing muscles at the sides having to work harder because of the ball, the involvement of the muscles in the legs also changes.
Crunch (on stability ball) technique
During training, one of the thigh muscles is often also engaged unconsciously. The rectus femoris is one of the quadriceps muscles. It is the only quadriceps muscle that crosses not only the knee joint but also the hip joint.
The rectus femoris brings the thigh toward the pelvis and the lower part of the spine, and vice versa. It is a so-called hip flexor and therefore brings the thigh forward from the hip joint. This also happens when the torso is brought too far toward the thigh during an abdominal crunch, causing it to begin to resemble a sit-up.
On a stability ball, you are less inclined to tilt from the hips, so the rectus femoris will also be less involved in the active movement.
For stabilization, however, the muscles in the legs have to work harder than during a normal crunch. The hamstrings and calves, for example, ensure that you do not roll off the ball.
Greater range of motion
On the stability ball, the range of motion also changes. Your back is not lying flat on the floor, but is tilted backward by the curvature of the ball (hyperextension). You therefore move it from an arched position to a straight position and then into a rounded back. You skip that first step during normal crunches.
Bosu ball as an alternative
The Bosu ball can be used as an alternative. It is a half ball with a flat surface on the underside. This allows you to retain the greater range of motion, while the legs and oblique abdominal muscles have to work less hard to stabilize.
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