Trying to get more speed on your serve? You maybe to trying hard and serving well for a few games then it becomes a real effort, muscles are sore. How do other guys look so smooth in their windup and look like they are not swinging so hard yet get such a fast serve in? Maybe you are approaching the serve all wrong. Think of it in a mechanically, the serve as a lever system. You want leverage and speed. The best way would be a class 3 type lever system. This gives minimal effort for the fastest speed. Remember you have to serve every other game and you need your serve to hold up. Every lever had a weight, fulcrum and force. Think about that. A pro serve is a class 3 lever. The fulcrum is at the legs and pelvis while the force is torso and arms, the weight is the tennis racket. For many amateur tennis players, the fulcrum is the wrist or elbows or shoulders and the force is the lower body and racket being the the weight. this is a class 1 type lever,effective for transfering the force to the racket but not racquet speed. If you dont understand the concept of mechanical levers then look it up at wikipedia.