Raising Aces: All About Injuries

Pitching mechanics are a bit like long-snappers in football, in the sense that we hear about them only when something goes horribly wrong. Mechanics rarely enter the discussion until a pitcher gets hurt, but when an ace succumbs to injury, the village folk grab their torches and pitchforks to go on the hunt for blame.

Experience has taught me that there is rarely an isolated cause for a pitcher's injury, with confounding variables that include mechanics, conditioning, workloads, genetics, and plain old luck. The pitching delivery is a high-performance machine, with a multitude of moving parts that must work efficiently in concert for the system to perform at peak levels, and any weak link in the system can lead to a breakdown.

The crew at Baseball Prospectus has been at the forefront of injury research at the sabermetric level, with experts from Will Carroll to Corey Dawkins fighting the good fight to identify many of the risks associated with playing baseball. Among these discoveries is the concept of “cascade injuries,” a term coined by Carroll to describe the common scenario in which an athlete will alter their mechanics in order to compensate for an existing injury, touching off a ripple effect that leads to another injury elsewhere in the kinetic chain.

Carroll and Nate Silver pioneered an idea known as the “injury nexus,” which describes the phenomenon that pitchers under the age of 25 have a much greater risk of breaking down than their veteran counterparts. The heightened danger of the injury nexus could stem from the fact that these players are still growing at a time when their workloads are greatly increasing. Major-league teams have heeded the lessons of the injury nexus in recent years, monitoring the pitch counts and innings of pitchers until they reach physical baseball maturity.  

BP soldiers Keith Woolner and Rany Jazayerli came up with a technique to measure workloads, using the system of Pitcher Abuse Points (PAP) to quantify the labor imposed on arms throughout the league. The PAP system uses a baseline of 100 pitches and begins counting for each pitch that ventures past that boundary. The idea is that pitches are more taxing as a pitcher becomes fatigued, with the 100-pitch threshold serving as an approximation of when fatigue begins to set in. The system is an excellent proxy for relative workload, though it’s not perfect, as each individual player has a unique threshold for when fatigue truly sets in and that barrier is dynamic during the season. Randy Johnson may not have fatigued until he reached 120 pitches in his prime, while the exploits of Pedro Martinez past the 100-pitch mark are legendary.

The mechanical link to pitcher injuries is the main attraction, drawing attention away from most of the other risk factors when a great player goes under the knife. Sherlock Holmes will come out of the woodwork to point out the smoking gun behind the death of a pitcher, but consider me a conspiracy theorist who claims that the majority of pitcher injuries have multiple assailants. It may be more convenient to point fingers in a single direction, but a thorough investigation of an injury requires that we study all the evidence.

That said, there are a handful of mechanical patterns that have been identified as precursors to injury, including a pair of risk factors that we studied at the NPA. The first mechanical precursor that we found should be familiar to regular readers of Raising Aces, given the continual emphasis on postural instability. We discovered that pitchers with considerable spine tilt were more prone to arm injuries, and the research was taken a step further by our colleagues at ASMI, where Dr. Glenn Fleisig broke down both components of arm slot to determine the stress on the elbow. Fleisig found that peak elbow varus torque was impacted by both the angle of trunk tilt and the angle of shoulder abduction at release point, adding another injury precursor to the list and further damning the conventional coaching advice that says to “get on top of the ball.”

Another mechanical cue to injury risk is an elbow that drags behind the shoulder-line as the pitcher squares to the target, with the throwing arm laying back into maximum external rotation. A relatively new discovery, elbow-drag is difficult to see without hi-speed cameras, as the critical moment occurs in just a couple hundredths of a second. The elbow lag can result from improper timing, particularly from a hard-throwing pitcher who uses an excessive delay of trunk rotation to increase torque after foot strike. There’s a soft boundary between the velocity-related benefits of extra torque and creating so much delay that the arm fails to catch up to the rest of the body. The elbow lag often occurs in conjunction with a heavy scapular load, where a pitcher will effectively pinch the shoulders such that the elbows are positioned behind the shoulder-line when trunk rotation fires. The pictures below demonstrate the difference, with Cole Hamels (left) establishing a strong elbow position at maximum external rotation, but Chris Sale (right) demonstrating an elbow that drags behind the shoulder line.

Scapular loading is another technique that pitchers use to increase hip-shoulder separation and gain precious ticks on the radar gun, though it has also been identified as a risk factor for injury. The strategy is a sidekick to the modern-day legend of the “inverted W,” another potential precursor that has gained considerable traction among the all-consuming baseball masses. The inverted W describes a pitcher who raises his elbows above the shoulder line (for the biomechanics student, that's hyperabduction above the acromial line) as he hits foot strike. The I-W is thought to produce additional valgus stress on the elbow, particularly when trunk rotation triggers and the throwing arm transitions into maximum external rotation, putting the ulnar collateral ligament (UCL) at risk.

A scapular load is often paired with the inverted W, though pitchers such as Randy Johnson have displayed a massive scap-load while keeping the elbows below the shoulder-line. The jury is still out on the predictive value of the inverted W with respect to arm injuries, though the high-profile data points have been mounting with the likes of Adam Wainwright, Johan Santana, and Stephen Strasburg. The W might rear its ugly head at foot strike, but the risk occurs when the pitcher initiates the rotational elements of the delivery, and the physical raising of the elbows above the shoulder line is less harmful than the elbow-position at the start of trunk rotation. Not to keep picking on Chris Sale, but the young southpaw has a pronounced inverted W in his delivery (right), offering a stark contrast to the abduction angles of Greg Maddux (left) in the pictures below. 

The greatest risks occur during the arm acceleration phase of the delivery, beginning with trunk rotation through max external rotation and into peak velocity at release point, where joint integrity is tested at maximum intensity. The hardest throwers are at the greatest risk of injury, by virtue of the additional kinetic energy as well as the heavier workloads bestowed upon aces. Increasing the kinetic energy in the system is going to put more stress on the joints, and the key to healthy performance is to maximize mechanical efficiency and structural stability. The injury precursors that have been identified are merely indicators of risk, far from perfectly reliable, and they are vulnerable to the influence of surrounding chain-links, a point which is driven home by the frequent appearance of pitchers who display a scapular load that precipitates an inverted W, leading to elbow-drag and making it nearly impossible to isolate a singular cause of injury.

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The Prior Strikes Back
Not to sound overly dramatic, but the injury history of Mark Prior is this generation's most frustrating example of conventional wisdom gone awry.

After being selected second overall in the 2001 draft, the right-handed phenom needed just nine starts in the minors before he was mowing down hitters in the Show. Prior dominated immediately, but a career that started on the fast track to the Hall of Fame was derailed by injuries before he could reach the next station. Prior's mechanics were labeled as flawless by anyone with a pair of eyes and a slant toward player evaluation, with a delivery that encapsulated the visual representation of scout-speak favorites such as “smooth” and “effortless.”  The disappointment that resulted from Prior's continued trips to the trainer's table created a cloud of judgment that hovered above the masses who had assumed that perfect pitching mechanics were an impenetrable shield to injury, and the public backlash was fueled by angst that was directed toward his supposedly impervious delivery.

Mark Prior had a slight inverted-W paired with a strong scapular load, and hindsight evaluations have honed in on these elements in a rush to blame Prior's mechanics for his injuries. Such theories have persisted despite the presence of several other well-known risk factors, with Prior toting red flags related to age, workload, and the cascade effect of injuries. In addition, any insistence on blaming his delivery completely ignores the fact that Prior's major injuries did not occur while throwing a pitch.

In July of 2003, Prior collided with Marcus Giles while running the bases, suffering a strain in his throwing shoulder that would keep him out of his first All-Star game. The Cub right-hander would miss only a few starts before returning to the mound in August, and he dominated over the season's final weeks. The Cubs were undeterred by any risk of cascade injury and rode their 22-year-old ace hard down the stretch, with Prior posting pitch counts of 131, 129, 109, 124, 131, and 133 over six September starts. Prior would toss another 133 pitches in the 2003 NLDS against the Braves and would exceed 115 pitches in each of his NLCS starts versus the Marlins.

All told, Mark Prior threw 235 innings in '03, violating Tom Verducci's “Year-After Effect” while sitting right in the thick of the injury nexus, putting in his most strenuous work at the end of his longest season as a pro after coming back from an arm injury during the high-pressure environment of a pennant run. Prior compiled the third-highest PAP total in baseball in '03, despite the missed starts and before counting the 43,000 PAP that he accrued in his playoff appearances.

Under such circumstances, it is a miracle that Prior pitched at all in 2004. The injuries started early, with a busted Achilles' tendon in spring training, an ailment that sidelined him until June. Prior was limited to just 21 starts and a disappointing stat line, though that can be understood if there were mitigating factors occurring inside his arm.

The wunderkind came back with a vengeance in 2005, cruising through the first several weeks until disaster struck again in late May, when a 100-mph line drive off the bat of Brad Hawpe struck Prior in the elbow, resulting in a compression fracture that put the right-hander back on the shelf. Ever resilient, the tenacious Cub came back once again in rapid fashion, taking just a one-month hiatus before making his return to Wrigley. Prior would finish the '05 season with the third-highest PAP in the league for the second time in three seasons, again having pitched a half-dozen fewer games than the other leaders, all while he was still climbing out of the injury nexus at the age of 24. 

A strained shoulder would crop up the following spring and delay his arrival until June, with continued shoulder woes ending his 2006 season after just nine forgettable mid-summer starts. The right shoulder has never been the same, and multiple surgeries have uncovered existing damage to Prior's prized pitching arm. A 2007 exploratory surgery by Dr. James Andrews revealed structural damage to the shoulder that may have existed for years, while a 2008 procedure addressed a torn anterior capsule in the shoulder, which is one of the toughest injuries to identify via MRI. Johan Santana is one of the first examples of a pitcher to successfully come back from the injury, and the diagnostic obstacles indicate that other pitchers may have unknowingly dealt with capsule tears that went undetected.

It has been nearly six years since Prior's last major-league pitch, and though we are left to guess at the root cause of his fragility, the sheer multitude of risk factors is nothing short of overwhelming. It leaves one wondering how Prior's pitching mechanics could possibly overshadow the usual suspects that are sitting right in front of us. Prior fell victim to virtually every known precursor, from extreme workloads during the injury nexus to traumatic collisions and injury cascades, yet the consensus view of his career is one of mechanical failure.

Many people are ignoring the facts in favor of selective reasoning to blame mechanics alone for Prior’s health struggles, despite these myriad risk factors that splatter the landscape of his injury-laced career. His mechanics GPA was off the chart, with elite marks in every category across the board: ideal balance and posture, excellent momentum, plus-plus torque, and amazing repetition of timing. It is certainly possible that mechanics contributed to Prior's injury risk. However, it is also a tribute to his mechanical efficiency that he was able to perform so well under such harsh conditions. The collective understanding of pitching has devolved thanks to the popular misconception that Mark Prior had bad mechanics.

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“You have to be open-minded. Closed minds don't make progress.”—Nolan Ryan

I am an admitted skeptic of conventional wisdom, particularly those theories that have been widely accepted in the face of glaring evidence to the contrary. The issue takes on additional heat when discussing injuries, especially in a competitive environment where athletes constantly challenge their own physical boundaries in order to improve performance. A heavy scapular load might be harder on the body, but the potential reward will drive pitchers to put themselves at risk in order to gain a few ticks on the fastball. My unconventional advice for these pitchers is to buy a surfboard and hit the waves, as paddling is an ideal exercise for building the back-side shoulder muscles that are critical to scapular load. As we used to say at the NPA in San Diego, “we never had a bad-armed surfer.”

Pitching mechanics support function as well as safety, but the lines blur at the extremes of player performance. A pitcher might have exceptional mechanical efficiency that produces 100-mph fastballs on a consistent beeline to the target. However, the player will only last as long as his body can handle the kinetic toll.