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April 29, 2014

Baseball Therapy

Do Innings Limits Work?

by Russell A. Carleton


Let’s go back to 2012, when the Washington Nationals made one of the most controversial decisions in recent memory by shutting down pitcher Stephen Strasburg late in the season, even though it meant that Strasburg, though not injured at the time, would not pitch for the Nationals in their Division Series. The Nationals lost that series to the St. Louis Cardinals three games to two, and Lana del Rey wrote “Summertime Sadness” as a result (no, not really). The Nationals justified that decision by saying that they wanted to keep Strasburg below 160 innings pitched for the season to prevent him from further injury. In 2011, Strasburg only pitched in five games, spending most of the season recovering from Tommy John surgery. He was healthy through most of 2013 and has been so far through 2014.

Flash forward to 2014, where a laundry list of starters (Jarrod Parker, Patrick Corbin, Jameson Taillon, Kris Medlen, Brandon Beachy, Josh Johnson, and Matt Moore) have already reported to Dr. James Andrews’s office, and we’re not even out of April. Could something have been done to save them? Perhaps the Nationals had it right. Maybe taking it easy with Strasburg in 2012 was the right move.

Today, we’re going to look at the tricky subject of innings limits for pitchers and whether or not they actually “work.” That is, do they show any effect on a pitcher’s health later in his career? But before we jump in, let’s discuss something first. I’m going to be looking at this from a public health perspective. Injury prevention is likely best done with actual X-rays of a pitcher’s elbow and shoulder and a firm understanding of his mechanics and how those mechanics put stress on his joints. But, in the same way that knowing a man is overweight tells me something (but not everything) about his chances for developing heart disease, we can look at innings workloads as an indicator. In the aggregate, do they help or hinder a pitcher’s health? If the answer is yes, then we can at least say that teams should have a bias toward innings limits or not.

Warning! Gory Mathematical Details Ahead!
I gathered stats on the number of innings that pitchers threw, whether in MLB or the minors, from 2000-2013, along with the number of games in which they appeared, the number of batters that they faced, and the number of pitches that they threw. I cross-referenced that with BP’s injury database, which lists both day-to-day injuries for players (when they are reported) as well as trips to the disabled list for that same time period.

For these analyses, I looked only at shoulder and elbow injuries (separately) that required a trip to the disabled list. Because we know that a really good predictor of whether you will suffer an elbow injury this year is whether you suffered one last year, I coded whether the pitcher had experienced an elbow (or shoulder, as the analyses dictated) injury last year or two years ago.

I took all pitchers in their age-23 season who pitched in MLB that year and coded for whether they made a trip to the DL for a shoulder-related issue during that year. That’s a binary outcome (yes/no), so I used a binary logistic regression. I entered as a predictor their previous shoulder injury status, along with their innings pitched stats for their ages 19-22 seasons (again, with inning counts from both the minors and majors)—that is, all data that would have been available up to that point. I also included the total number of cumulative innings pitched up to that point. As expected, last year’s shoulder injury held up as a good predictor of this year’s shoulder injury risk, but innings pitched in the age-22 season also had a significant effect.

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11 comments have been left for this article. (Click to hide comments)

BP Comment Quick Links

Repperson29

Has there been a study on cold weather pitchers injury rate to their throwing arm compared to warm weather pitchers? Or two sport athletes compared to those who just pitch all year?

Apr 29, 2014 03:54 AM
rating: 0
 
ericpost

The answer is "sort of" to both questions:

Kaplan et al. (http://www.ncbi.nlm.nih.gov/pubmed/21051421) found significant changes in shoulder strength, range of motion, and pitch volume for warm weather pitchers that may make them more susceptible to injury. However injury rates between cold and warm-weather pitchers was not directly measured.

Olsen et al. (http://www.ncbi.nlm.nih.gov/pubmed/16452269) found that pitchers who threw more months out of the year and participated in more showcases were at a higher risk for injury. While this isn't directly looking at two-sport versus one-sport athletes, pitchers who are throwing competitively more months out of the year and participating in more showcases would in theory be more likely to be specializing in baseball and would have less time to pursue a second sport.

Apr 29, 2014 09:53 AM
rating: 2
 
Lagniappe

Good work again, Russell.

John Smoltz states that it is not the total number of pitches but the number of high stress pitches that lead to injuries. Could the Batters Faced data be weighted with a leverage index, and the same with innings pitched?

Apr 29, 2014 05:37 AM
rating: 1
 
smitty

The aspect of this type of study that makes it so hard is not knowing what a guy did as an amateur. I'm pretty sure youngsters hurt their arms pitching in high school and in these other leagues that kids play in nowadays. I'm pretty certain there are not many coaches who are well schooled in the proper care of a very young arm.

I first thought of this when reading about two time Tommy John procedure man Kyle Drabek. He threw a ton of pitches and innings in high school, especially in the State Championship Tournament. I believe that sent him very far down the road to UCL surgery. I'm curious regarding the current crop of victims and their amateur experience.

Apr 29, 2014 07:42 AM
rating: 2
 
BP staff member Russell A. Carleton
BP staff

Yeah, there's that aspect of it. I wish I had a way around that...

Apr 29, 2014 07:46 AM
 
Behemoth

While I realise they aren't directly comparable, I wonder if Japanese pitchers tend to get more elbow injuries given the popular perception that they throw an awful lot more at a very young age.

Also, with someone like Strasburg, I wonder if having TJ surgery has a different impact on the likelihood of injury when compared to other injuries which may not require surgery, and may thus leave the elbow structurally weaker. I know that when guys like Medlen and Beachy were diagnosed this year, some of the experts were surprised as they thought that there was a period post-Tommy John when pitchers were relatively safe from another UCL injury.

Apr 29, 2014 08:02 AM
rating: 1
 
Andy Cochrane

Great as ever, Russell. Thought provoking as well.

Apr 29, 2014 08:54 AM
rating: 0
 
gjhardy

Regarding the number of innings vs batters faced issue, I was wondering if all those warmup pitches start to take a toll. I would think not, since warmups are not generally thrown with a lot of stress. But a pitcher who goes seven innings has thrown an extra 35 (? I'm not sure how many warmup pitches are allowed per inning) pitches that day.

Apr 29, 2014 09:33 AM
rating: 0
 
Geopipp

Great work Russell.
There is something to be said for the difficulty of an inning. If a pitcher throws 90 pitches mostly from the stretch he's going to be gassed. If you have a pitcher throwing from the windup the same amount of pitches he'll tell you that he could go another 20 pitches. I was wondering how much of impact throwing from the stretch has on this discussion. The mechanics are different and more comes from the arm and less from the legs. Surely the difficulty of the inning, and possibly using a calculation of runners on base to add another variable might have some impact? Food for thought.

Apr 29, 2014 10:41 AM
rating: 0
 
mattseward

Would be great if the same study was done on velo for pitchers and is that corollated with injuries. I have heard some talk on velo spikes being an indicator, albeit anecdotally

Apr 30, 2014 00:17 AM
rating: 0
 
tristramshandy

Very interesting article. I wonder if the effects of more innings is magnified for a pitcher (like Strasburg) who's already had TJ surgery. If so, then sitting him during the playoffs looks like a smarter mover.

Apr 30, 2014 09:07 AM
rating: 0
 
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