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Tommy John Surgery and Pitch Frequency, Part II

After completing two studies comparing characteristics of pitchers headed toward Tommy John surgery with the league average pitcher, we look to the academic research arena for assistance on interpreting the results.

Ronald Martinez

Recently I introduced the most complete list of players who have undergone Tommy John surgery to reconstruct their UCLs in an effort to extend their professional baseball careers. With the list in hand, I investigated two characteristics of pitching in comparative studies between pitchers that were headed toward Tommy John surgery and the average major league pitcher. For both studies, two major confounding variables were controlled to help isolate the characteristics being studied. The controlled variables were pitching role (i.e. starter or reliever) and age.

Pitch Type/Frequency

The first study was aimed at determining whether pitchers on a path to Tommy John surgery throw any particular types of pitches more frequently than the average pitcher. The results shown in the table below indicate that pitchers headed for Tommy John surgery in the near future threw slightly more fastballs and sliders than the league average peer, at the expense of slightly fewer curveballs and changeups.

Years Prior FB% SL% CT% CB% CH% SF% Sample Size
2 years prior 1.37% 0.43% 0.03% -1.83% -0.35% -0.08% 105
1 year prior 0.93% 0.50% 0.08% -1.29% -0.17% 0.26% 138
Year of TJS 1.04% 0.96% 0.25% -1.35% -0.82% 0.28% 110

Summary from Author

Based on these results, the best that I could say in the previous article was that the findings make some intuitive sense. I have seen some articles in the past noting that throwing a lot of sliders can lead to increased potential for arm injuries.

To do much better than this, we consulted someone who is familiar with the latest academic research in the field of pitching biomechanics in an effort to determine whether these findings align and whether the differences are meaningful.

Question and Answer with Eric Post, Illinois State University

Q: Would you mind introducing yourself and describing your area of academic research?

A: My name is Eric Post and I am a graduate assistant and master’s student at Illinois State University. I work as the athletic trainer for the Illinois State baseball team and I am currently pursuing my master’s degree in athletic training. My area of interest for my master’s thesis is the correlation between peak fastball velocity and peak torque at the elbow and shoulder during pitching.

There have been studies examining the effects of increased velocity on injury and studies examining the effects of increased torque on injury, but only one to my knowledge that directly examined the relationship between velocity and torque. This study was performed with high school pitchers whose average fastball velocity was 71 miles per hour. My hope is to examine the correlation between these two variables in a more advanced population of pitchers (high level collegiate pitchers) with fastball velocities more comparable to those seen in professional pitchers.

Q: What is it about baseball biomechanics research that interests you the most?

A: I think what interests me the most about biomechanics research is that there is still so much to be learned about the biomechanics of pitching and how certain biomechanical factors are related to injury and performance. There seems to be so much disagreement in the baseball community about what constitutes "good" versus "bad" pitching mechanics with a large amount of the evidence in support of one viewpoint or another based on anecdotes and case studies. I think biomechanical research analysis provides an exciting opportunity to use scientific data to determine more effective ways to pitch that reduce the chance of injury.

Q: The results of the study showed that pitchers heading for Tommy John surgery tend to throw slightly more fastballs and more sliders than the average pitcher in their peer group, while throwing slightly less curveballs and changeups. Does this finding make sense given your own research and/or readings of biomechanics research papers?

A: Before I begin, it’s probably best to go over some background information that will be helpful to understand. When talking about Tommy John surgery we are talking about a repair of a damaged or ruptured ulnar collateral ligament, or UCL. When a pitcher reaches maximum external rotation during the throwing motion there is a strong valgus torque at the elbow that is trying to distract, or pull apart, the medial aspect of the elbow. The UCL (and surrounding musculature and bony anatomy) acts to provide a counteracting torque and stabilize the elbow. Therefore, when researchers want to measure stress on the UCL they will either measure the valgus torque that the UCL must counteract, or the actual counteracting varus (also called adduction) torque.

While measuring the torque at the elbow is not a direct measure of stress on the UCL since muscles of the forearm and the bony anatomy of the elbow also counteract the valgus torque, Morrey et al. ( showed that the UCL is responsible for the majority of the resistance to the distracting force at the elbow (approx. 55% of it). Additionally, Hurd et al. ( found increased UCL thickening (an adaptation to stress) in pitchers who threw with higher torque at the elbow. Therefore, measuring torque at the elbow appears to be a reasonable way to quantify stress on the UCL.

Ok, I know that was a bit wordy but I think it’s important to understand going forward. Hopefully everyone is still awake. As for the relationship between certain pitch types and increased stress on the elbow, it has traditionally been believed that the curveball is a more harmful pitch than the fastball or change-up. This had led to recommendations by the American Orthopaedic Society for Sports Medicine that youth pitchers refrain from beginning to throw curveballs until the age of fourteen (

However, in a biomechanical study using 3-dimensional analysis, Dun et al. ( compared the elbow varus torque produced by the fastball, curveball, and change-up in a group of youth (11-14 year old) pitchers. They found that the fastball produced significantly more varus torque than the curveball and that the change-up produced significantly less varus torque than the other two pitches. Additionally, Nissen et al. ( analyzed high-school pitchers using 3-dimensional motion analysis and also found that the curveball produced significantly less varus torque at the elbow than the fastball.

There have also been non-biomechanical studies examining the relationship of pitch type to injury. Olsen et al. ( retrospectively examined a group of teenage pitchers (14-20 years old) and found no significant difference between a group that sustained an elbow injury and a non-injury group in the age the pitchers began throwing breaking balls. In a 10-year prospective study performed at the American Sports Medicine Institute by Fleisig et al. ( there were no significant differences found in the age of first throwing curveballs between a group of healthy youth pitchers and a group of youth pitchers who retired due to injury or had surgery.

They also found that pitchers who threw curveballs before the age of 13 were no more likely to be injured than pitchers who began throwing curveballs after the age of 13. Additionally, Lyman et al. ( followed 476 youth pitchers (9-14 years old) and found that throwing a slider was associated with an 86% increased chance of elbow pain.

So based on current research it seems to me that when it comes to elbow injury and torque it may not necessarily be the type of pitch thrown that matters but rather the velocity with which the pitch is thrown. Fastballs and sliders are thrown at higher velocities than curveballs and change-ups and therefore it may be expected that pitchers who throw these pitches more often may be at a higher risk for elbow injury. It must be noted, however, that the majority of research that has been done and that I have cited here was performed on youth and teenage pitchers. This is due to the large interest in preventing injury in developing pitchers and as a result the findings from these studies may suffer from poor generalizability to professional pitchers.

Q: Would you say that the biomechanics research community is united in this viewpoint regarding pitch types? Are there other recent studies that have come to alternative conclusions?

As just a master’s student with an interest in the biomechanics of pitching, it’s hard for me to speak for the entire research community. The best I can do is provide a summary of the literature I have reviewed and give my interpretation of overall themes and findings. In my opinion, it appears that there is a shift occurring away from the commonly held belief of the curveball being a more dangerous pitch, especially for youth pitchers.

It is very important to note that in a biomechanical study of collegiate pitchers Fleisig et al. ( found no difference in elbow varus torque between the fastball, curveball, and slider. They did find that the change-up produced significantly less varus torque than any of the three other pitches. Therefore, there was no significant difference in the amount of stress at the elbow between the fastball, curveball, and slider in this group.

This more advanced group of pitchers may use a different technique to throw these breaking pitches, which may lead to the differences seen between this study and the research done on younger pitchers. This study must be kept in mind as we are attempting to examine pitch type frequency changes in a group of professional pitchers, whose pitching technique is probably more comparable to the college group in this study than the younger pitchers in the studies mentioned earlier.

Time for a bit of a tangent-- While the biomechanical research done on youth pitchers seems to show that curveballs are actually less stressful on the elbow than fastballs, it is still recommended by many respected health organizations and youth baseball organizations that pitchers refrain from throwing curveballs until they master the fastball and change-up. Even if the curveball is less stressful than other pitches, I personally believe this is still a good recommendation.

Youth pitchers who throw a curveball before their peers may be at a competitive advantage, and thus may risk being overused by their coaches. Pitching volume and overuse, above all other risk factors, appears to be the most predictive of injury in youth pitchers. I know this isn’t directly related to the topic of pitch type selection and Tommy John surgery in professional pitchers, but I think it’s important to talk about.


We have learned that there are published papers that arrived at conclusions that agree with the direction of the findings from this study. This allows me perhaps to feel more comfortable that despite the relatively small deltas observed in the studies, there is more substantial evidence backing these findings.

For a more scientific look at the results of the pre-Tommy John surgery pitch velocity study, stay tuned for the next in this series of articles.

You can follow me on Twitter at @MLBPlayerAnalys. <a href="" class="twitter-follow-button" data-show-count="false">Follow @MLBPlayerAnalys</a>
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You can follow Eric Post on Twitter @posteric. <a href="" class="twitter-follow-button" data-show-count="false">Follow @posteric</a>
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Sincere thanks to Eric Post for providing his time, effort and knowledge in answering these questions. Credit and thanks to Fangraphs for data upon which this analysis was based.