The two primary ways to increase baseball throwing velocity are strength training and improving the mechanics of the delivery. Some of the most important muscle groups to build for a pitcher or position player are the legs, the midsection and the rotator cuff.
The two elements, strength and the delivery, work hand in hand to maximize pitching velocity. While not all pitching coaches are proponents of weight training since it can cause injury, recent studies have shown that weight and strength training can improve velocity and, if done properly, can reduce the risk of injury that might occur during the repetition of the throwing motion that starting pitchers perform during games.
Steven Ellis, a former Major League Baseball pitcher, details his training regimen at thecompletepitcher.com. The program consists of an extensive list of his recommended stretches and exercises designed to improve velocity and accuracy, and to reduce risk of injury. The program includes delivery mechanics, such as applying direct force to the back of the baseball, stabilizing the lead leg and rotating the torso during the pitching motion, as well as strength training tips. The ultimate goal of the delivery is for the pitcher to develop a smooth motion that allows for full bicep and elbow extension, with good pelvis and torso rotation as he breaks toward the plate.