Pro Power Drive Brace Adult Hitting Trainer By using the Pro Power Drive Brace it won't let your hitter throw their hands out, so they can focus on other areas of their hitting while using it. After 15-minutes of using the Pro Power Drive Brace your speed will gain a minimum of 5-mph. Remember, There is NO substitute for developing Proper mechanics in any part of your game. It fits an upper arm dimension of 14" in diameter or more.