An important part of an athlete’s training program is core strengthening, mainly in the form of abdominal muscle strengthening. To strengthen the abdominal muscles most players do the crunch and/or variations of the crunch.
The crunch is a good exercise, but because it develops mainly (if not only) the upper portion of the abdominal musculature, it is of limited value. Most sports skills involve more of the lower abdominals and the oblique muscles located on the sides. Because of this, emphases should be on development of these latter muscles and not just the upper portion of the abdominals.
To strengthen the lower portion of the abdominals, which play an important role in quick movement on the field, ring or court, you should do the reverse sit-up, sometimes called the reverse crunch. Keep in mind that the lower abdominal muscles are involved in rotating the pelvis backward. This movement is needed to allow for easy forward movement of the thigh, the key to a quick first — and second — step.
When executing this exercise you should be sure to start with your thighs perpendicular and to return to this position on each repetition. If you instead lower the feet to the floor you will be using momentum to get the legs/pelvis rotated. This results in less strengthening of the muscles, especially as they are involved in the sports actions that they must perform.
When first getting started you may have to push down with your hands to help raise your hips (and legs) and to ensure adequate rotation of the pelvic girdle. In the ending position, your knees should be close to your chest. Keep your head and shoulders as relaxed as possible throughout the upward movement
For maximum muscle involvement, you must use your lower abdominal muscles to start the pelvic girdle rotation. Once you can do the exercise easily, place your arms over your head resting on the floor. In this position, you will have to rely solely on pulling with your lower abdominal muscles. For some athletes the exercise then becomes difficult.
To strengthen the obliques you should do exercises such as the reverse trunk twist. For the more advanced athletes, the Russian twist is best. In the reverse trunk twist it is important that the shoulders remain flush to the ground. If your shoulders rise on each repetition have someone hold them down so that you can get a maximum stretch (and strengthening) of the muscles at the same time.
For most effective execution the Russian twist should be done on a Glute Ham Back machine. It should not be done on a medicine ball or in a seated position. These variants of the Russian twist do not allow for full range of motion strengthening and stretching. In addition, the Glute Ham Back machine allows for precise positioning so that you get full and effective development of the musculature.
The reverse sit-up and Russian twist are excellent stretching and strengthening exercises. In the reverse sit up you stretch not only the abdominal musculature, but also the muscles of the lower back. When doing the Russian twist on the Glute Ham Back machine you get maximum tension of all the abdominal muscles to hold the horizontal position and to rotate the shoulders a full 90° in both directions.
The stretching that occurs is with the muscle tension which is what takes place in most sports. These are not passive stretches. They are active or dynamic stretches because your abdominal muscles must contract strongly to get you into the end positions. Thus, you strengthen and stretch as you do the exercises.
The reverse sit up and Russian twist are much more important exercises than the crunch for athletes. They duplicate more closely what takes place in different activities such as running, kicking, throwing and hitting. The upper abdominals however, are mainly involved in overhead throwing and hitting together with the lower portion.
For more information on the role and execution of these exercises see Biomechanics and Kinesiology of Exercise.