Pitchers get injured. That is no news flash as throwing a baseball at 90-100 MPH is an unnatural act which stresses the body to its physical limits and sometimes its breaking point. With that understood, there are ways to prevent injuries to pitchers, and it all comes down to physics & bio-mechanics.
A MLB pitcher must have correct mechanics to maintain a healthy and sustained career. This is true for relievers as well as starters. In this article, the proper motion for pitching a baseball will be illustrated & described. Anyone with an interest can learn and apply these correct techniques to their own motion. Pitching coaches must know everything described below, or else their efforts with kids are of no value, or even worse– destructive.
Let’s start with proper mechanics. The most critical position for a pitcher to maintain throughout the loading part of his wind-up is the “Flex-T” position. Both shoulders need to be locked into this straight-line posture, in order to avoid excessive strain on the shoulder capsule and the elbow. From there both forearms are flexed, which minimizes strain throughout the kinetic chain. Below is Nolan Ryan, one of the greatest & most durable power pitchers of all-time (late in his career), locked into the Flex-T:
Fatigue is the enemy that cripples pitchers with correct mechanics. The photo below is an illustration of the most common mechanical flaw in pitching, which is over-rotation of the upper arm/shoulder. This is the proverbial, “reaching back for something extra” doesn’t really help, in fact it’s damaging. If the shoulders are not held into a straight-line posture, the excessive strain will lead to shoulder/elbow breakdown, unless immediately corrected with a strong Flex-T posture:
Analyzing a pitching motion can be difficult, as many things are happening in the <2 seconds it takes a hurler to deliver the ball to home plate. While reviewing video, it is helpful to pause and scroll it forward manually– frame by frame. Using this method, we will evaluate some of the best pitching motions in the game, as well as some problematic ones.
The hardest thrower in MLB is Aroldis Chapman, who just signed a 5-year/$86M deal with the NY Yankees. Focus your attention at 21-22 seconds into the video, which is the best view of his motion in this clip:
Aroldis Chapman has fluid & flawless mechanics, which is what creates all his power. He over-rotates his hip turn, but still holds everything together throughout his motion because he’s such a great athlete. This reduces his injury risk considerably (although not absolutely), which is what Yankee GM Brian Cashman needs on a 5-year deal for a power pitcher. The key to longevity will be for Chapman to remain strong & flexible in the hips & core. Here’s more science on what make Chapman so extraordinary:
Chapman disagrees with how Cubs used him in postseason 12-16-16 
If I was Aroldis Chapman, I’d be upset with Joe Maddon too, as he was abused– by any rational definition of pitcher handling. No one appreciates being abused. Yes, it won the Cubs a WS, and yes he’s well-paid, and that’s why they play em’, and flags fly forever, etc…, but Chapman (at least) should have been informed by his manager that he was planning on using him extensively in both games 6 & 7– and clearly he’s saying he wasn’t. It’s his career (and a lot of $$) at risk, pitching fatigued, so he had a few parting words out the door. Anyone who can’t understand that is a hypocrite and/or has never competed. I would love to hear Joe Maddon’s thoughts on all this.
BTW, Yankee fans should be ecstatic, as Brian Cashman has done the impossible which is to replace Mariano Rivera.
One of the most durable and effective starting pitchers of this era is Justin Verlander of the Detroit Tigers. Not surprisingly his motion is extremely compact & efficient. Note the beautiful balance throughout his delivery:
Not heeding the principles of sound mechanics & thermodynamics has catastrophic consequences for pitchers, as well as teams trying to build & maintain a staff. Here’s Tyson Ross, whom the San Diego Padres just released, despite being one of the best pitchers in the NL from 2013-15. Ross over-rotates his shoulders, and doesn’t use enough hips in his delivery, which has led to his shoulder problems:
Below is Steven Strasburg, the celebrated #1 overall pick by the Nationals in 2009, whose MLB career has been one injury issue after another. It’s not hard to see why, as the right shoulder severely flies out, creating all kinds of stress on the rotator cuff & ulnar collateral ligament (UCL). This is the game which he was taken out of last season, before being shut down. Note that Strasburg has pitched 200+ innings only once in his 7-season career:
Below is a really poor motion, that deserves scrutiny. RHP Zach Lee is from Texas, listed as 6’4″, 227 lbs– age 25. Scouts would project this kid to be sitting at 95-96 MPH and touching 98 with his fastball, with a 92-93 MPH wipe-out slider. The slider in the video rolls in at 88 MPH, and is a “hanger.” The Seattle Mariners just released him for fear of what Mike Trout does to pitches like that. Everything describes hereafter happens at 3-4 seconds:
Look for Lee’s forearm being nearly vertical as he starts his rotation towards home plate. This leads to the eventual “forearm fly-out,” seen clearly at mid-rotation. This severely stress the UCL, causing velocity/control loss and eventually leads to TJ surgery. Lee also doesn’t pronate at the finish, another major mechanical flaw which leads to velocity loss and eventually soft-tissue breakdown of the elbow and/or shoulder. Lastly, his drive-line ends up towards the lefty batter’s box, instead of straight home. His push-off the rubber could also be improved, and his hips are sluggish– which is really the root of all his problems.
The most likely reason Zack Lee stinks is because he’s hurt– due to faulty mechanics. The Padres just claimed Lee off waivers, and if he is ever going to pitch effectively for them, he needs an immediate MRI of the right elbow & shoulder along with both hips– as there is major damage in there.
Injuries must be evaluated & diagnosed first, followed by a treatment plan for full recovery & rehabilitation. Next, the pitching mechanics must be corrected. It needs to be a total commitment by everyone from the player, to the coaching & medical staff, or else it fails. It’s a lot of science, but it’s also that simple.
Addendum 1-4-17: The San Diego Padres are considering a 6-man rotation in 2017. The traditional & sabermetric argument against 5-man rotations (vs. 4-man rotations) is that the ace gets less starts. The Padres don’t really have that problem, as they don’t have a true ace. Luis Perdomo is probably their opening day starter, and the Padres have high hopes for him, but no one claims he can match up consistently with Clayton Kershaw or Madison Bumgarner– who are true aces. The issue the Padres have is keeping their arms healthy, which means limiting their innings. A 5-man rotation asks for 32.4 starts per pitcher, meaning #1 & #2 get 33 starts over 162 games. A 6-man rotation asks for 27 starts per pitcher. Since the drop-off in quality isn’t as much of an issue as limiting fatigue and preventing elbow & shoulder blowouts, the benefits are clear in this case. Even with an injury, the fall-back is #7 starter, or a 5-man rotation until the pitcher has healed. This is a good year for the Padres to experiment, as they have nothing to lose on the field.
One last point on a 6-man rotation is that it doesn’t limit innings on a pitcher who is effective and can handle the workload. If a starter averages 7 IP in 27 starts, then he will pitch 189 innings. 7.1 IP/start is 198 innings, etc… It’s about economizing and going deeper into games, when they’re ready. A 6-man set-up will allow teams the flexibility to stretch some guys out, while protecting others.