Serve - Is raising the hitting shoulder the last big stretch? Background - My interpretation of some biomechanical research results on the serve- During the service motion, first, the tossing shoulder is up and the hitting shoulder is down. Then the hitting shoulder is very rapidly moved high using trunk lateral flexion. Last, the final racket head speed is increased to ball impact using mostly internal shoulder rotation. Internal shoulder rotation contributes the most to racket head speed. The internal shoulder rotators are pre-stretched by the leg thrust. The stretch occurs because the upper arm is at about 90° to the body and the racket and forearm are at about 90° to the upper arm when the legs thrust up and carry along the shoulder. This externally rotates the shoulder stretching the internal shoulder rotator muscles. The internal shoulder rotator muscles are the lat (Latissimus Dorsi), pec (Pectoralis Major), Teres Major and some others. The largest muscle connected to the arm is the lat, the second largest is the pec. Both insert on the front of the upper arm at the same location and internally rotate the shoulder by pulling on the humerus at that insertion point. The question is what part does raising the hitting shoulder play in farther stretching the lat or in maintaining the stretch? Apparently it is well known that raising the shoulder can increase the lat stretch. From the Manual of Structural Kinesiology, C. Thompson, R. Floyd, 15th ed., page 89: paraphrasing The stretch (of the lat) may be increased ................by then laterally flexing and rotating the trunk to the opposite side. (This is a great basic reference. It is a popular college text and the latest edition is $75 while the recent editions like the 15th are just $10 or so.) Lateral trunk flexion is just the side bend that puts the hitting shoulder up. Rotation of the trunk is just the trunk turn that is used for serving. Both of these lat stretches can easily be felt by just holding the upper arm at 90° to the body and rotating the forearm up and back as in the service motion to give the internal rotators some stretch. When stretched in that way, laterally(side) bend the trunk, feel the lat stretch. Also rotate the trunk and feel the lat stretch. In Knudson's book, Biomechanical Principles of Tennis Technique, I think he discusses the speed of stretched muscles as more rapid. Does this late trunk flexion and rotation play an important part for the serve by final stretching of the lat for added racket head speed?