Kinesiology of Exercise
Crunches and sit-ups develop mainly the upper portion of the abdominals. To develop more of the lower abdominals, you should do the reverse sit-up.
Major Muscles and Actions Involved
In this exercise the lower portion of the abdominal muscles, especially the rectus abdominis, shorten to perform spinal flexion. In this action the lower pelvic girdle rotates up and toward the upper trunk. This involves an opposite rotation of the pelvis in comparison to what occurs in the sit-up or crunch.
The reverse sit-up is an important exercise for all sports that require abdominal strength to rotate the pelvis posteriorly to produce a maximum ROM to rotate the legs up high. Thus, gymnasts perform this exercise to develop the muscles needed to raise their legs to a 90-degree angle or higher in many of the stunts executed on the apparatus and in free exercise. Likewise, it is an important exercise for dancers, especially for developing the muscles needed to raise the legs in ballet leaps and in modern dance.
- If you want to also involve the upper abdominal muscles, continue bringing your pelvis and bent legs up and over until your knees are above your head. Doing this produces a maximal stretch of the spine. However, this is an advanced movement and is not a key element of the reverse sit-up. The main factor in successful development is to have the pelvic girdle fully rotated off the floor, at which point the lower abdominal muscle fibers are maximally contracted.
- In the beginning movement of this exercise, you may find it helpful to press hard with your hands against the floor to assist you in getting your pelvic girdle rotated up and over. More importantly, if you want maximum muscle involvement, you must use your lower abdominal muscles to start the pelvic girdle rotation. Once you can do the exercise more easily, you should place your arms over your head. In this position you will have to rely solely on pulling with your abdominal muscles.
- Do not return your feet to the floor during execution. Doing so will create momentum in your legs, which makes it easier for you to rotate your lower pelvis upward. This in turn, means that the following initial stage of raising your legs is done by your hip joint flexors, not your abdominals.
- As you become more proficient, to make the exercise even more difficult, do not return your thighs to the vertical position. Keep them bent toward your chest so that there is zero moving inertia and a strong initial abdominal muscular contraction.
- To execute a more difficult version of the reverse sit-up, you can do the exercise on a decline bench. In this case, you must hold onto something, which will automatically assist you in raising your pelvis. But you still get greater contraction of the abdominals. Execution is the same as on the floor.
- The reverse sit-up is an excellent stretching and strengthening exercise. When you bring your knees up close to your chest when your pelvic girdle rotates off the floor, you actually stretch your lower back muscles greatly. This is not a passive stretch but an active one because your abdominal muscles must contract strongly to place you in this position. Thus, you strengthen your abdominals as you stretch your lower back.
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