Stability is best understood in terms of the opposite notion, instability. In tennis, a stroke or action is unstable if a small fluctuation in the starting position or any intermediate position results in a large change in the final position.

In simple terms, a stroke or motion is unstable if a small error in the stroke is amplified into a large error in ball path.

A stable stroke is one in which a small error in the initial position or any intermediate position leads to a small error in the final position.

For power tennis, every aspect of your stroke must be stable from the takeback the start of the stroke to the strike, and all movement in between.

This requires that all joints be held as firmly in place as possible with a minimal of movement. By "freezing the shoulder, elbow and wrist, the body actually becomes more elastic and the potential for transferring energy along the kinetic chain increases. This is why one sees professional players straining every muscle at the point of contact.

Stability at each joint, stability through the core of the body that connects the legs to the shoulders, and the platform stability are all significant in power tennis.