Still, according to experts in biomechanics, that 100-mph ceiling isn't an illusion—it's a basic property of human physiology. A pitcher generates momentum by rocking onto his back leg and thrusting forward. After that he rotates his pelvis and upper trunk, then his elbow, shoulder, and wrist. Intuitively, it seems like building up the muscles in the legs, upper body, arm, and shoulder would generate more force and make his arm move faster. The reality: There's a point when more torque doesn't yield a faster pitch. It simply causes tendons and ligaments to snap, detaching muscles from bones and bones from one another. (Tendons connect muscles to bones; ligaments connect bones to each other.)
Glenn Fleisig, a biomechanical engineer who studies pitching at the American Sports Medicine Institute in Birmingham, Ala., has calculated that about 80 Newton-meters of torque act on an elite pitcher's elbow when he throws a fastball. The ulnar collateral ligament connects the humerus and ulna—two of the bones that come together in the elbow. To test the outer limits of the ligament's strength, Fleisig subjected cadaver elbows to increasing amounts of rotational force. These experiments showed that an average person's UCL snaps at about 80 Newton-meters. Smoky Joe Wood said that he threw so fast he thought his arm was going to fly off. It turns out he wasn't far from the truth.
Another way to test the proposition that ligament fragility limits velocity is to see what happens when pitchers strengthen their muscles. Mike Axe, an orthopedic surgeon and protégé of Fleisig's partner James Andrews, advises pitchers to build up their shoulder muscles by practicing with a weighted glove on their throwing hand. According to Axe, a pitcher can add up 2 to 5 mph to his fastball with this regimen. The potential gains are lower for those who throw fast to begin with, though. Axe has seen pitchers increase their velocity from 84 to 88 mph and from 88 to 91 mph. He's never seen anyone improve from 98 to 100. The chief benefit for these hurlers is that they suffer fewer muscle tears.
Why do sprinters keep getting faster while baseball pitchers seem to have maxed out? Because track athletes don't approach the limits of what human tendons and ligaments can handle. When you run the 100-meter dash, no single stride represents as violent a motion as the arm makes during a single overhand pitch. Sprinters can build up their muscles without worrying that the extra force will rip their ligaments apart—that's why steroid use seems to make sprinters faster but won't help pitchers generate velocity beyond a certain point. (A better reason for a pitcher to take steroids would be to decrease the time it takes to recover between games.)
Ligaments and tendons can get stronger, but at a much slower rate than the muscles that surround them. There are rumors that pitchers who've undergone Tommy John surgery—that is, a replacement of the UCL with a tendon from the hamstring or wrist—can throw harder than they did before having surgery. But any increase in velocity probably has less to do with getting a new superligament than with the strict rehabilitation program Tommy John patients are supposed to follow. The reason pitchers get injured in the first place is that their muscles, tendons, and ligaments weren't as strong as they should have been.
