I had posted several links on a tennis website more than a dozen years ago. Unfortunately, most of those links are no longer valid. But I did come across a video from an episode of Sport Science (ESPN) from a while back that discusses the effect of using increased weight for golf and baseball: You might also try some research on Overload-Underload Training. I believe this type of training was initially developed for various track and field events -- particularly where objects are utilized or thrown. It was subsequently applied to baseball and other sports. For the Overload phase of the training, the mass of the implement or the projectile is increased somewhat to develop strength. However, the mass (or MOI / swing weight) is increased no more than 20%. Increases greater than this can significantly alter joint / muscle recruitment and swing mechanics. The next phase is the Underload phase where mass (or MOI) is decreased from the norm by (no more than) 20%. This phase is intended to develop power -- bat speed, club speed, racket speed, throwing speed. Note that both of these phases will tend to alter swing timing (or throwing timing). So, a 3rd phase is often employed, using a normally weighted implement or projectile, in order to re-establish proper timing.