***Note, huge thanks to Jeff Zimmerman for all of his help with this piece***
The sad news that prospective St. Louis Cardinals Ace Alex Reyes was going to miss the 2017 season was devastating news for the Cardinals organization. Reyes looked to make a huge impact in the Cardinals rotation with absolutely devastating Stuff (according to the Stuff Metric, the only starter with better Stuff was New York Mets Starter, Noah Syndergaard). To figure out how Reyes came to break down, let’s look into the scientific literature on UCL injuries.
The first paper I’d like to draw on, was published by David Whiteside and Colleagues, from the University of Michigan (Whiteside et al., 2016). Their method used a machine learning approach, and deduced there were 6 risk factors that could be used to predict UCL reconstruction surgery. These risk factors were 1) Fewer days between consecutive games, 2) smaller repertoire of pitches, 3) a less pronounced horizontal release location, 4) smaller stature, 5) greater mean pitch speed, and 6) greater mean pitch counts per game. How did Alex Reyes measure up in these risk factors?
Reyes started the season at AA, where he started in 14 games and pitched 65.1 innings. At the Major League Level, he pitched 46 innings, and started in 5 games, while appearing in 12 total games. Excluding those pitchers who appeared in less than 10 games in a season, the average days between consecutive games in the MLB in 2016 was 4.37 games. At the major league level, Reyes had an average of 4.64 games.
How about the repertoire of pitches? In the 2016 season, starting pitchers had on average, 3.5 +/- 0.82 pitches in their repertoire. For a pitch to count as part of the repertoire, I included it in the analysis if it was thrown 10% of the time. Reyes had 4 pitches – A fourseam fastball, two seam fastball, curveball, and change up. These were thrown 35.8, 28.0, 12.0, and 24.2% of the time. So, Reyes threw more than the average number of pitches – so, this isn’t cause for concern based on this study.
How about release location? The horizontal release point league average for Alex’s 4 pitches in 2016, was 1.72 feet – that’s the average absolute horizontal release point (collapsed across righties and lefties). Alex’s release point was 1.74 feet – so, it was actually a more pronounced release point than the league average.
What about stature? Alex Reyes is a tall guy – standing 6’3, and weighing 175 lbs. The league average height for players born since 1985, is 6’1, and the average weight is 209.8 lbs – from the Lahman database. The Whiteside paper only mentions height though, and given that Reyes is taller than most other players, this doesn’t appear to be a risk factor. Reyes is taller than most, but extremely lean at 175 lbs. We’ll come back to this, shortly.
Now, on to the one smoking gun in this paper. Pitch velocity.
Alex had a peak average fastball velocity of 96.8 mph (for his fourseam fastball). That’s a heater, and it represents a fastball velocity with a z-score of 1.51 – well above league average. Why is velocity so stressful? I had written about UCL stress and velocity, using data from Driveline baseball (Sonne, 2016). The fine folks at driveline baseball examined pitch velocity and compared it to predicted UCL stress from the Motus Baseball sleeve. Simply put, as velocity goes up, so does UCL stress (figure 1). In fact, accounting for nothing other than pitch velocity, we were able to explain 37% of the variance in the UCL stress using only pitch velocity – nothing about mechanics, height, or weight.
More recently, those same researchers published data that the UCL stress was reduced when throwing offspeed and breaking pitches, but when normalized to pitch velocity, the stress was much higher in these types of pitches (O’Connell et al., 2017). Reyes throws an 88 mph change up – which could represent significant stress on the UCL based on these data.
Figure 1. Examining the relationship between ball velocity and UCL stress using the Motus Sleeve. Data from driveline baseball (https://www.drivelinebaseball.com/), and article available at http://www.mikesonne.ca/baseball/pitch-velocity-and-ucl-stress-using-the-motus-sleeve-further-interpretation-from-driveline-data/.
So finally, we are left with pitch count per game. Lumping together starters and relievers, the average pitch count per appearance was 45.6. The average pitches per inning was 14.5 in 2016. Reyes had 5 starts, and 7 relief appearances, and his average pitch count per outing was 65.6. Comparatively, his pitches per inning was 16.5 – which could lead to additional fatigue when compared to the league average.
So where do we point to the source of injury? The short answer? We have absolutely no clue.
In the field of ergonomics, we examine injury risk as an interaction of force, posture, and repetition. Workload metrics like pitch counts, and innings counts, give us insight into repetition. The forces can be inferred from the pitch velocity. Where our PITCHf/x data lacks, is giving us insight into the posture, or, the pitching mechanics. A very interesting piece was writen on Viva El Birdos regarding the poor mechanics that Alex Reyes exhibited.
Chris O’Leary has been very active in self promoting his analysis of Reyes’s very risky mechanics, and has predicted for some time that Tommy John Surgery was inevitable for Reyes. The problem baseball is currently faced with, is there is no reliable way of measuring mechanics without the use of motion capture systems. Right now, mechanics are not quantified to the extent they should be, and without a large, public database (like we have for PITCHf/x), it’s hard to completely infer the role that mechanics and timing have when contributing to injury risk.
Early this week on FanGraphs, there was a piece mentioning how Noah Syndergaard’s weight gain could increase his risk of injury (Sawchik, 2017). Compared to Alex Reyes, Syndergaard is a massive man (compared to human beings, he is a massive man). Theoretically, that added muscle mass may in fact keep Syndergaard from getting hurt. That added muscle can help him stabilize his UCL during the pitching motion – an advantage that the slight Alex Reyes did not possess at 175 lbs. During the throwing motion, the stress on the UCL exceeds the known force level for tear of the ligament. It is the role of the muscle to help take some of the stress off of the passive tissues (like the ligaments) during the throwing motion. Of course, someone like Chris Sale tends to be the outlier that challenges this hypothesis.
With respect to the workload Alex Reyes faced – he pitched less than 120 innings at all levels in the 2016 season. This alone does not represent an elevated risk of injury. What we can’t see from the PITCHf/x data, is how his workload variability changed from moving from a pure starter role at the minor league level, to a reliever and starter at the major league level. If you would like to delve into some mind blowing hypotheses on injury, check out the webinar from the Baseball Performance Group. They identify that it may be the variability in workload that poses a risk to pitchers – and not the overall workload itself. Moving between different roles would definitely increase the variability in rest times for Reyes.
Assessing the injury risk of pitchers is a challenging proposition. There is no single silver bullet, but understanding the scientific literature and examining the role of multiple factors is the way forward in trying to determine what might have gone wrong.
References
Whiteside, D., Martini, D. N., Lepley, A. S., Zernicke, R. F., & Goulet, G. C. (2016). Predictors of ulnar collateral ligament reconstruction in Major League Baseball pitchers. The American journal of sports medicine, 44(9), 2202-2209.
O’Leary, C. (2017). Pitching Mechanics Overview Alex Reyes. Retrieved from http://chrisoleary.com/pitching/PIP/Overviews/Reyes_Alex_PitchingMechanics.html, on February 16, 2017.
Sonne, M. (2016). Pitch Velocity and UCL Stress using the Motus Sleeve: Further Interpretation from Driveline Data. Retrieved from http://www.mikesonne.ca/baseball/pitch-velocity-and-ucl-stress-using-the-motus-sleeve-further-interpretation-from-driveline-data/, February 16, 2017.
O’Connell, M, Marsh, J., Boddy, K., (2017). Fastballs vs. Offspeed Pitches – Comparative and Relative Elbow Stress. Retrieved from https://www.drivelinebaseball.com/2017/02/fastballs-offspeed-pitches-comparative-relative-elbow-stress/, February 15, 2017.
Sawchik, T., (2017). Thor is Bigger, Stronger… and Riskier? Retrieved from http://www.fangraphs.com/blogs/thor-is-bigger-stronger-and-riskier/, February 15, 2017.
The Red Baron, (2017). The Changing Mechanics of Alex Reyes. Retrieved from http://www.vivaelbirdos.com/2017/2/15/14613328/the-changing-mechanics-of-alex-reyes-delivery-breakdown-carlos-martinez-injury, February 15, 2017.
