Photo Study of Andy Roddick's Serve

Most of the racquet-head speed on a serve comes from the straightening of the elbow from the 90-degree bend you see here. Having the elbow up and the racquet down ensures that full bend, and the elbow's high position also results in a high point of contact with the ball. As the elbow straightens, all of the upward forces from legs through forearm cause the wrist to whip upward and forward, moving the racquet at tremendous speed from the 90-degree angle it forms with the forearm here to 180 degrees (aligned with the forearm) at contact and then well beyond 180 degrees, as we shall see in upcoming photos.