Two key actions for producing force in the golf swing, tennis groundstrokes, baseball/softball hitting, hockey and other hitting actions are weight shift and hip rotation, collectively known as clearing the hips or getting the hips into the hit. These movements use the hip muscles and set up the abdominals for a powerful contraction to rotate the shoulders forward.
Because most players do not have the physical ability to execute these movements through a full or adequate range of motion, they rely mainly on the arms for greater force in hitting. But swinging harder with the arms eventually leads to elbow, shoulder or wrist problems, which in turn can prevent you from playing. Also, since the abdominals see little action when they are not fully prepared for action, they do not contract as strongly and thus have less effect on the mid-section.
To be injury free, to hit with greater force and to slim the hips and waist, use your hips to full advantage. Keep in mind that lateral and rotational movements of the hips can produce up to 30-40% of the total force generated in a swing. In everyday movements, however, the muscles involved in these mid-section actions are hardly used! By fully involving the hip and mid-section muscles, you can almost double your power while you slim down the waist because of the effective work that these muscles undergo.
To maximize your force, you must first have weight shift, ie, you must push your hips (where your center of mass is located) forward in the golf swing and/or take a step forward in tennis, and baseball/softball hitting while maintaining the head and shoulders basically in place. This action shifts your weight onto the front leg at which time your hips rotate around the forward leg.
To isolate the hip action, be sure to keep the shoulders back in the side-facing position (although they may shift slightly forward if the hip slide is very vigorous). If your shoulders move forward and rotate together with the hips, you will not get the additional force of shoulder rotation, resulting in less involvement of the abdominals.
To learn effective hip and shoulder rotation actions and to develop a muscular feel for them, practice shifting the hips forward while in a side-facing position (hip abduction) and rotation of the hips forward while keeping the shoulders back. Use the Total Athlete System™ for resistance and the elasticity of the cords to pull the hips around as soon as you start them in rotation so that you can learn the action and how it feels.
The abdominal muscles and actions are effectively developed by doing the reverse trunk twist and Russian twist or rotating the shoulders against the resistance of the Total Athlete System™. Sorry, but the crunch exercise is not effective in developing the rotational ability of the abdominal muscles.
By mastering weight shift and hip rotation, the power you generate in the golf swing, tennis groundstrokes, baseball/softball hitting, etc., will be much greater. At the same time you will be slimming down the hips and waist by involving and constantly using these muscles during play.
These exercises are explained in detail in Explosive Golf, Explosive Tennis, Kinesiology of Exercise and Body Shaping. For more information on how you can improve your athletic performance read Build a Better Athlete.