Each of the four abdominal muscles play a distinct role in execution of various sports skills. For example, when throwing a baseball, football or javelin for maximum distance or speed, the rectus abdominis contracts with great force to “whip” the upper body forward. Prior to the rectus going into action, the internal and external obliques rotate the shoulders forward.
In the soccer throw-in there is maximum involvement of the rectus abdominis to flex the spine to release the ball from relatively straight arms. Flexing the spine from an arched position is also seen in diving, in execution of various gymnastic stunts and in trampolining.
In the martial arts, especially in judo and some forms of karate when throwing or hitting an opponent, the internal and external obliques play a very important role in rotating the shoulders to produce force. The rectus comes into play when throwing the opponent over the body.
In hitting sports such as golf, boxing, and baseball batting, the internal and external obliques are involved in rotation of the trunk (shoulders). They play their major role most effectively when the hips are first rotated forward to place the oblique muscles on stretch.
Running athletes need especially strong internal and external obliques to hold the shoulders square to the running direction, which in turn helps to hold the hips square so that the leg action is forward and back. In sports such as football, athletes who run with the ball must have strong obliques to rotate the shoulders while keeping the hips facing in one direction in order to elude an opponent.
Another extremely important function of the abdominal muscles is in breathing, more specifically, forced expiration. In normal breathing the abdominals do not come into play. In sports it is often necessary to quickly inhale, forcefully exhale and to hold the breath. The major muscles involved in forced expiration are the internal and external obliques and the transverse abdominis which is especially powerful in this action. The transverse abdominis is best developed through forced expiration against resistive devices such as The Breather. As a result you get great development of the muscles involved and in many cases a flatter abdominal wall.
Contrary to popular opinion, the abdominals do not play a significant role when lifting weights. For example, when doing the squat it is mainly the erector spinae muscle that is involved to hold the normal curvature of the spine and to stabilize the trunk to support the weights on the shoulders. The abdominals are relatively relaxed. If you instead contract the abdominals when doing such exercises the erectors will have to relax and you will loose the spinal curvature creating a very dangerous situation. In addition, in sports such as walking and running it is mainly the erectors that play a role in holding the trunk erect. The abdominals remain relatively quiet except for the obliques to prevent trunk rotation.
Because of the important roles played by the abdominals, the muscles should be strengthened in each of their main actions. This means doing exercises such as the sit-up and reverse sit-up for the rectus abdominis, the reverse trunk twist and Russian twist for the internal and external obliques, and forced expiration with The Breather for the transverse abdominis.