With proper use weighted baseballs can be an effective tool for increasing throwing velocity of a regulation weight baseball. A number of training studies have been conducted using underload/overload baseballs utilizing a large range of weight variations (4 ounces to 17 ounces with most being 5 ounces +/- 20%). These studies indicate velocity improvements can be achieved, with some velocity gains reported as significant. In general terms, overload (more than 5 ounces) weighted balls are thought to increase arm strength while underload (less than 5 ounces) weighted balls are considered to increase arm speed.