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Muscles work in groups, most often working for opposite goals. Doing an arm curl works the biceps, but the triceps are also firing in order to control and counterbalance the effort. Otherwise the body would flail out of control when we tried to do anything. This concept is key to understanding what shoulders do.
The shoulder can achieve 16,000 different positions because of a lack of skeletal restraints and the versatility of the small but tough muscles that move it. Keeping the shoulder moving in the precise positions that maximize power but avoid injury is a job that taxes the shoulder even when it's done right.
When a pitcher's arm is cocked, the shoulder's external rotators are dominant. Then as the arm comes forward, the arm is internally rotating, providing the power behind the pitch. There are five muscles that rotate internallyand only three external rotators.
When the pitcher whips his arm over his head to release the ball, the shoulder blade (scapula) needs to be stable to provide a fulcrum for the motion, and that requires a lot of muscle activity to just keep it in the proper place. During this phase, the upper arm bone (humerus) rotates 100 degrees in .05 of a second. Those wires really jump with bioelectricity when this is happening. After the ball is released, the elbow and wrist and hand throw off the excess kinetic energy, with posterior shoulder muscles firing to control the deceleration. The entire operation depends on the preceding step, like gears turning in a motor.
The hands, forearm, and, sometimes, sandpaper determine the type of pitch that's thrown, putting brutal spins on the ball and subjecting batters to complex rules of physics in the milliseconds it takes the ball to cross the plate.
In Marshall's opinion, Rivera somehow scuffs the ball because it "moves even when it shouldn't." But in any case, Rivera doesn't pitch enough innings to let hitters get used to his pitchesor pitch. "He pitches so seldom he gets away with a one-pitch technique," says Marshall. When it comes to mechanics, Marshall doesn't see any pitcher who stands out, but he does give Rivera his due: "He has a good style for the one pitch he throws. He applies force very well. He doesn't get his body as far forward as he should, but that's no big deal."
And that's because, at the end of the day, all the training, study, debate, and surgery pale before intangible elements, like natural athletic ability. As pitchers make their way into higher levels of competition, though, their arms suffer for the success, asked to perform at the peak of their engineered ability. But that doesn't mean those magical pitching arms should be coddled.
Marshall's regimen for pitchers includes relentless training of the muscles specific to the task of pitching, including lifting weights. Other experts advise to shy away from weight training, fearing that the arm will wear out. Not Marshall.
"You have to stress these ligamentsyou have to," says Marshall. "You have a lot of force acting on the body no matter what you do. What you don't need is unnecessary force.
"We don't treat the arm like it's fragile, like it's going to break. We make the arm so damn strong it will never break."