Finding Clues to Hitters’ Shoulder Injuries

Compensating for injury changed Matt Kemp's swing for the worse (via Keith Allison).

Compensating for injury changed Matt Kemp’s swing for the worse (via Keith Allison).

I have spent a lot of time the past few months contemplating general movement patterns in hitters and how they relate to the mechanics of the swing. I have looked a lot at the hitters I work with personally, as well as those I watch in professional baseball. I am fascinated by how the human body organizes itself to swing a bat, and its amazing ability to coordinate these movements and compensate for deficiencies to create the results we see among different types of hitters. Every year, a number of hitters have to weather injuries to the shoulder, and here I present some introspection into what role swing mechanics play in how hitters deal with these maladies.

Injuries resulting in missed time are only part of the equation. I also want to see what similarities in patterns are associated with shoulder problems, and how the swing plays a role in compensation. This way, we can have a better idea how the body moves most efficiently and what happens when it does not work properly. Rather than offer the simple explanation that shoulder injuries sap ability to hit for power, we can make more educated observations about how an injury to the area will affect a hitter as an individual. From a swing development standpoint, this method can also provide clues about how to avoid lost production from a weakened shoulder.

I do think improper movements in the swing over a long period cause or at least increase potential for problems. However, as I noted in my previous article on wrist injuries, it is difficult to find athletes who will admit that the way they hit or throw a baseball is a factor contributing to injury. If you think this sentiment is imaginary, talk to pitchers who have had to undergo Tommy John surgeries, and see how many will blame their pitching mechanics.

For this study, I looked at all the position players who spent time on the disabled list during the 2013 season due to a shoulder injury, regardless of the cause. There were 20. Though I do know of a few players who injured their shoulders on swings at the amateur level, none of the reported cases last year attributed their maladies to their batting. Because throwing tends to be the most common irritant of shoulder problems, I ignored the cases where the throwing shoulder was the site of injury to reduce the noise associated with throwing mechanics.

This weeding out process left me with five hitters: Matt Kemp, Scott Van Slyke, Paul Janish, David DeJesus and Ryan Kalish. Kalish sat out the entire 2013 season and has had a multiple year history of neck and shoulder issues; as such he probably warrants an entire case study on his own. For the purposes at hand, since he did not play in the big leagues last year, I excluded him as well, given the lack of swings or video to analyze, leaving me with just the four players. All four hitters dealt with collisions of some kind, and were affected on their front shoulders in relation to their hitting stance.

So let’s go through some functional anatomy of the shoulder before getting into specific cases.

Shoulder Bone Anatomy

The only bony attachment between the shoulder and the rest of the body is the collarbone (clavicle), making the soft tissue attachments more important than in other joints. The bone that runs the length of the biceps and triceps in the upper half of the arm is called the humerus. It sits securely in the joint, intimately supported by the four rotator cuff muscles. Their primary movement function is to rotate the arm, naturally. Internal rotation turns the elbow away from the body; external rotation turns it in toward the ribs. The rotator cuff attachments are shown here:

Rotator Cuff

The long head of the biceps is considered in many applications to be the fifth rotator cuff muscle, as it directly helps stabilize the humerus as it moves. It runs over the top of the humeral head and inserts directly into the labrum, the smooth ring of ligament tissue that serves as the seat for the bone. For the humerus to rotate most efficiently, it needs to stay in close contact with this seat, called the glenohumeral fossa. If its proximity is stretched, it pulls on all the muscles that hold it in place and makes it less stable to transfer force down through the rest of the arm.

Biceps Labrum

In overhand throwing, this relationship is vitally important. As the arm is lifted higher above the shoulder, the head of the humerus wants to pull away from its seat. Eric Cressey has an outstanding video that describes this process in relation to the shoulder blade in more detail.

In it, he explains how as the shoulder girdle lifts up out of its resting position on the rib cage, the rotator cuff ligaments are required to take on more responsibility for stabilizing the head of the humerus so it does not ride up and out of the relatively shallow socket. Asking these muscles to create force at the same time leads to a movement primed for breakdown, especially given the comparatively small size of these muscles. For throwers, this can manifest in many different ways, the most severe of which is a tear in the labrum. If the labrum is compromised, (among other issues) the head of the biceps can no longer anchor the humerus in the shoulder joint, leading to decreased ability to rotate the arm at high speeds.

This is one reason (as I understand it from a non-expert perspective) why diminished velocity tends to indicate a shoulder issue more often than an elbow problem. The area is less stable and cannot deliver the same force, since the muscles are pulling on a bone that is more mobile in the joint rather than a relatively fixed one. Of course, compensation for this weakness can also lead to the elbow breaking down first, making the usefulness of this rule fairly limited.

How does all this apply to hitting? During the swing, lifting the front shoulder off the rib cage beyond a certain point leads to the same problems, albeit usually under much less stress than with throwing. We should see an increased use in the larger, slower muscles around the shoulder to help support it, like the deltoid, trap, lat or pectorals. The deltoid and trapezius muscles are great for lifting the shoulder straight up, and the pectorals and lat are excellent for pushing and pulling parallel to the ground (very basic definitions). But these are large, gross movements that are not as useful for rapidly moving a bat that weighs about two pounds.

These compensatory changes can either be an indicator of already present shoulder deficiency, or they can be the last line of defense to prevent injury to the glenohumeral complex. To demonstrate how the shoulder works properly, think about a backhand (a.k.a. tabletop) double-play feed from a middle infielder.

<a href=Rickie Weeks <a href=Dee Gordon

There is no recruitment of the bulky, powerful muscles around the shoulder necessary in this movement. The humerus internally rotates in its seat, turning the hand under the shoulder and delivering the baseball up and away from the body. This move is done without lifting the shoulder girdle off the rib cage, resulting in a quick and low-effort explosion of the arm. If the shoulder is lifted at all, it is the product of the movement of the hands. It’s a passive move, not active.

A Hardball Times Update
Goodbye for now.

From a coaching standpoint, the anatomy of the shoulder makes it even more ridiculous to have hitters LITERALLY take the hands directly to the ball. Besides the fact that hitters make contact with the ball at many different points in the swing, the shoulders just are not built to move the arms in straight lines in a rapid fashion. They work in circles. Mr. Miyagi knows what I’m talking about.

Sanda floor

As I have written before, it is fine to have certain hitters think in metaphorical terms to achieve the desired results. Sayings like “knob to the ball” are useful for some hitters to help keep the swing short. Just please realize that the reality of the swing is much more complex.

With that tutorial out of the way, let’s get into our case studies. We will look at each hitter individually, in chronological order by the start of each individual’s disabled list stint.

Paul Janish

  • On Disabled List: March 31, 2013
  • Off Disabled List: May 10, 2013
2012 186 .186 .234 .048 .503
2013 Post-DL 45 .171 .220 .049 .442

Janish’s shoulder injury actually occurred in September of 2012, and his recovery from offseason surgery leaked into the 2013 season. Here is a shot of the defensive play that did him in:

Janish Injury

On a diving play to his backhand side, he landed awkwardly on his side while his was outstretched and elevated above his shoulder. This is the same kind of position discussed above that does not allow for all the muscles securing the arm to properly protect the shoulder from injury. After the game, a telling quote from Janish summed up the chronic nature of his left shoulder’s instability:

I’ve probably done it eight or nine times before,” he said. “Usually, it just slides right back in. This is the first time I’ve ever had it get stuck and not be able to get it back in.”

His shoulder has a lengthy history of similar problems, giving us a good first example of what a balky shoulder does to a swing. Below are two swings from August 2013 that I felt were representative of his body of work in full:

Janish Away Janish Middle

No one will mistake Janish for a guy who will do a lot of damage with the bat, and how his front shoulder works contributes to that notion. The first swing is on a pitch away that he pops up into right-center field, and the second is a pitch in the middle of the plate that he deposits into right field for a bloop single.

In both looks, Janish appears to lock his front shoulder in as he loads his hands. As he brings his hands toward the ball, he has to fight to get his hands working under and around the front shoulder. The shoulder shrugs up slightly toward his head and neck to allow his hands to get through the ball. All this leads to a swing that looks muscled and forced, despite an obvious lack in explosiveness. There is no looseness to the swing, reducing his bat speed below the point where he could reasonably drive balls into the outfield on a consistent basis. I do not know enough about his history and training to be able to say his swing caused the shoulder instability, but I think it is fair to say they are correlated.

Since I would like you to keep reading—and I get bored watching Janish’s swing—let’s move on to our other hitters who are a little more fun to look at.

Scott Van Slyke

  • On Disabled List: June 11, 2013
  • Off Disabled List: June 28, 2013
2013 Pre-DL 74 .221 .559 .338 .843
2013 Post-DL 78 .262 .361 .099 .758

Van Slyke injured his shoulder on a diving play to his left on May 25, 2013. An article written shortly after the play initially described his injury as a whiplash type of feeling, more in the neck than the shoulder. Take a look here:

Van Slyke Injury

Similar to Janish, Van Slyke’s shoulder makes contact with the ground while the arm is stretched out to catch the ball, lifting the shoulder off his rib cage. Though he initially felt it more in his neck, there are various muscular connections from the shoulder to the neck and base of the head. He was likely feeling some referred pain above his shoulder from the fall, since in ongoing play it was known as a shoulder injury. He would play a couple more weeks before needing his trip to the disabled list. Van Slyke attributed a lack of power to the injury that continued to nag him until he was forced to spend time on the shelf:

I started cutting my swing off and being careful at the plate the last four days,” he said. “Being the lead shoulder in my swing, it was limiting how hard I could swing.”

To get a baseline picture of his swing before the injury, here are some shots of two doubles he hit the day prior to his diving play:

Van Slyke Early 2013 2B Pitcher Van Slyke Early 2013 2B Angle Van Slyke Early 2013 2B

Both of his shoulders are very active right from the start of his swing, making it look like his body, arms and bat all move together in one piece. He does not lift the front shoulder off the ribs like Janish did, but, because it locks out, there is a forced look to his swing, also like Janish. Luckily, Van Slyke has quite a bit more strength in his upper body than the offensively challenged Janish, allowing him to get away with not having better sequencing of his movements. Now, here is the last home run he hit before going on the disabled list, a week after he initially hurt the shoulder:

Van Slyke Pre-DL

And a swing just after returning from his injury break:

Van Slyke Post-DL Pitcher Van Slyke Post-DL Angle

Not much change. The shoulders still lock out at the start of the swing, using the bigger muscles to try to power through the ball. Van Slyke’s follow-through comes around his shoulders flat to the ground rather than loose and over his shoulders in a smooth rotation. Because he relies more on his strength rather than quickness to drive the ball, his injury (by his own admission) did not allow him to take his normal swing with the same kind of authority. Where a more efficient swing may have been less affected by the injury, his swing relies on that strength more than most, rendering him unable to compete at the same level as normal.

Just to see if there was any further change in his swing later in the year, I checked a bunch of his end-season swings for differences. Here is one, for example:

Van Slyke Late 2013

Same movements. Looking at his swings in total, I would suspect Van Slyke is less likely than most to have long-term effects from the injury simply because his shoulder does stay resting on his ribs throughout the swing. His swing relies more on his ability to drive the ball with the power of his core, rather than proper movement of his shoulders, the front in particular. The only real issue is his lack of natural lift to his swing as a result. He has to hit the ball in a perfect spot to elevate it because of how flat his swing path is. His is not a perfect swing, but the front shoulder itself probably will not be a cause swing instability going forward.

David DeJesus

  • On Disabled List: June 15, 2013
  • Off Disabled List: July 24, 2013
2013 Pre-DL 217 .260 .445 .185 .763
2013 Post-DL 222 .241 .356 .115 .692

DeJesus has a lot of solid qualities in his swing. He has a pretty good bat path and shares many movements with some of the best hitters in the game. As a result, he has been a consistent hitter over multiple years at the highest level. DeJesus fell prey to the wrath of a stubborn outfield wall during this play on June 14 of last year:

DeJesus Collision

Similar to the first two cases, DeJesus’ shoulder experiences a jarring impact while in an already weakened position as he reaches for a ball. Let’s see how he looked on one example of his swing the day before his injury with which he hit a home run to straightaway right field:

DeJesus Pre-Injury DeJesus Pre-Injury Front

As well as another drive from earlier in the year:

DeJesus Early 2013

Focusing on the front shoulder, you can see in the side view how it hikes up as soon as the hands start to move down into the plane of the ball. It then pulls up and away from the ball, and continues to actively pull back toward the catcher side of his body as his swing is launched toward the pitcher. The hands have to come in steep to the plane of the ball, and get pushed through to extension rather than the hands pulling the shoulder through. He does make this move in part with his spine and abdominal muscles, but you can still see how the shoulder lifts off the rib cage while a large amount of force is being put on it.

There are also a few swings where DeJesus keeps his front shoulder more quiet, though these are less numerous and consist entirely of the balls he drove to the opposite field. Most of his hardest hit balls, however, were to the pull side. Notice the collection of homers (black dots) and line drives (red dots) in and over right field:

DeJesus Spray

This approach does have its benefits in parts of the strike zone, especially in tight to his body where he can push his hands through the strongest. Courtesy of Baseball Heat Maps, here is an image showing DeJesus’ run values compared to the league during the 2013 season (catcher’s point of view):

DeJesus 2013

Sure enough, DeJesus has a nice little window of pain carved out in the inner third of the strike zone where he is well above average, while the outer two thirds are weaker. For some comparative glances, here is a swing a week after returning to game action:

DeJesus Post-Injury Pitcher DeJesus Post-Injury Front

And a couple views from swings later in the year:

DeJesus Late 2013 HR Pitcher DeJesus Late 2013 HR Front DeJesus Late 2013 2B

The shoulder does not rise up as much in the swings after his stay on the disabled list, though it still has the tendency to want to pull across the body. Whether that was a subconscious result of the injury or a conscious decision to alter his mechanics, it likely resulted in less stress on the joint. Notice how this affected his run value chart after the injury:

DeJesus Comp

This shows his production after the injury versus before, covering the 2013 season. Here we see that DeJesus actually performed better in the zone up and away, while not as well in the bottom half of the zone and a small portion up and in. Just my opinion, but favoring the shoulder may have resulted in less comfort getting the front shoulder to actively pull the hands up through the zone. This would make his swing flatter and more able to get to balls up and away, while slightly limiting the amount of force he could generate on balls down in the zone without the extra strength. As you can see from the side angle, DeJesus still had a small propensity for pushing his hands through, but not nearly as dramatically. Without the extra move in his front shoulder, his swing actually looks a bit smoother getting through the ball.

As an interesting but unfortunate tie-in to my last study on wrist injuries, DeJesus broke his hand on a swing earlier this season on June 19.

DeJesus Broken Hand

As with throwing injuries, inefficient movement patterns can cause problems at multiple connected links in the kinetic chain. I posit that DeJesus’ effort with his shoulders contributed greatly to the stress put on his hand, resulting in a broken bone. Hitters can still have freak injuries without an obvious cause, and I don’t claim that he could have avoided the injury with different mechanics. Maybe he slept on it wrong, and it was primed for breakdown regardless of the type of swing. I would only say his mechanics increased the chance of a problem that happened to come to fruition.

Matt Kemp

  • On Disabled List: July 5, 2013
  • Off Disabled List: July 21, 2013
2012 449 .303 .538 .235 .905
2013 Pre-DL 246 .254 .357 .103 .666
2013 Post-DL 44 .359 .615 .256 1.047

Kemp’s shoulder woes date back to the end of the 2012 season, when he crashed into the center field wall and dove for a ball in the same game, both hurting his left shoulder.

Kemp Collision Kemp Dive

In an article on a week after the injury, Dodgers trainer Sue Falsone confirmed that his swing was affected by the event, saying “Every time he swings, it irritates it.” He would go on to have offseason surgery to repair a torn labrum and rotator cuff damage.

Kemp’s swing before his 2012 injury was a thing of beauty, which despite the various other injuries he dealt with resulted in a pretty fantastic overall season.

Kemp 2012 Pitcher Kemp 2012 Front Kemp 2012 Back

He wasn’t the same hitter when he started the 2013 season, and his swing changes were relatively noticeable from the start.

Kemp Early 2013 Pitcher Kemp Early 2013 Front

Kemp began to use a much more active front shoulder at the start of the swing, making it look tighter and more labored. It shrugs up as the hands and back shoulder start to come down, and almost runs out of room to go. The shoulder gets elevated to an awkward position moving up and away from contact, and as a result his hands then have to be forced out to the ball to stay through it. Compare that to the looser, natural release his hands demonstrated in 2012.

Then Kemp’s shoulder couldn’t handle the workload any longer, and this swing put him back on the shelf:

Kemp 2013 Swing Injury Kemp 2013 Swing Injury Front

The shoulder rises up here again on a swing that reinjures it. Knowing what we have seen of how the shoulder is built, you can see how this is not a biomechanically sound position to be in. Any extra effort in the swing while in this position would result in a lot of strain on the joint. His shoulder, already being weakened from his previous injury and offseason surgery, is unable to deal with this stress.

In his first game back, Kemp had a nice game contributing a double and homer to his team’s effort in the same inning:

Kemp First Game Back HR Kemp First Game Back 2B

In the first clip, you could argue the shoulder does not lift up as early, but it clearly still has a mind of its own, pulling up off the rest of his body to bring his hands through. The second clip looks the same as his swings earlier in the season. Finally, here are some of Kemp’s swings from later in the season after his ankle injury on a few different locations:

Kemp Late 2013 Away Kemp Late 2013 Low Kemp Late 2013 Up-In

Still the same movement. In Kemp, I think we have our clearest case for a shoulder injury affecting the swing, causing a diminution in his hitting power. Whether his shoulder moves were his body’s way of trying to protect the joint or his attempts to create more force with extra muscles, we can’t really say. But I do feel pretty comfortable saying Kemp got himself into a pretty unfortunate loop of an injury leading to new movements, which then caused more problems for the injured area. All of this occurred while his numbers slowly spiraled downward from his MVP-type production.

With these four hitters, we have seen how similar shoulder injuries can manifest in different fashions. The commonalities in the mechanism of injury matches up well with our understanding of the shoulder and where it can be put in harm’s way. We saw some compensation for injuries, as well as cases where the swing itself may have caused a higher likelihood or recurrence of damage.

Beyond that, there are no sweeping conclusions to be drawn from these cases, just as there should not be any sweeping assumptions made about hitters with shoulder injuries without proper context. There are unique characteristics that make each player a big league hitter, and without understanding those differences you cannot assume any one specific outcome. One theme shows up here as in all athletic moves: efficiency. When the body is working efficiently, with all the parts moving together toward the same goal, there is much less chance for physical problems.

Loose, quick muscle firing supports the weaker parts of the body better than abrupt, sharp movements ever could. Onlookers will say sports look like they come easy to some and not others. The best athletes in the world make things look easy not because they are so much stronger and faster than everyone else. It is because they have figured out how to organize the body in a way that best suits their tasks without fighting themselves. Hitters who are dealing with injuries or learning how to swing should keep this goal in mind as well. As George Brett said, “You don’t get hits by trying hard. You try easy.” If you have to try hard, figure out what you’re doing wrong.

Dan is Fangraphs Lead Prospect Analyst, living in New York City. He played baseball for four years at Franklin & Marshall College before attending medical school. Follow him on Facebook and Twitter @DWFarnsworth.
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9 years ago

David Wright struggled this year,mostly because of a damaged shoulder caused by sliding head first on a steal. He, and his coaches, blamed the shoulder on changing his swing. Will be a great addition for a follow-up analysis in the future.

Thiago Splitchange
9 years ago

I think 2012 Chris B. Young would be a good case to look at as well. Hurt his AC joint running into the wall a few weeks into the season and hasn’t hit since.

Dan Farnsworth
9 years ago

There seems to have been a lot of cases this year; if there’s more interest I’ll do a follow-up this offseason.

9 years ago

Any chance on a followup going into 2015? Great stuff