This post follows up on last Monday’s post as it is critical for players and coaches to understand the roles of the hips and shoulders. The hips and shoulders are literally the central gears of the swing system. Your swinging movement begins with the muscles of the trunk. As they rotate the generated force works its way both up into the shoulders and down into the legs.
Muscle is required to initiate hip and shoulder rotation, and even more muscle is required to translate the generated force into efficient racket movement. So, if all this force is required, why aren’t tennis players more muscular? That’s because there’s a distinction between the force generated by the contraction of muscle and the force provided by the elastic action of muscle. Tennis swings require muscle elasticity, like a rubber band being stretched and released, rather than muscle contraction.
Another very important thing to understand is that in order for the trunk muscles to fire effectively, the forward rotation of the hips must precede the forward rotation of the shoulders. There is in fact a lag between hip and shoulder rotation that creates a stretching in the muscles of the trunk followed by an explosive snapping action of the shoulders. Increasing the total amount of hip and shoulder rotation will NOT necessarily increase the force of the swing. The amount of lag between the rotation of the hips and the rotation of the shoulders is more important than the total amount of rotation. This is the reason that the semi-open stance is so critical.