“” Challenges with Typical Biomechanical Analyses of Pitching - Driveline Baseball

Challenges with Typical Biomechanical Analyses of Pitching

| Pitching Mechanics, Research
Reading Time: 8 minutes

This is a guest post from Dr. James H. Buffi, Ph.D. in Biomedical Engineering.

It is impossible to overstate how excited I am to have Dr. Buffi contribute to our blog in what will be the first article in a three-part series on the biomechanics of pitching. In 2014, Dr. Buffi had a paper published title Computing Muscle, Ligament, and Osseous Contributions to the Elbow Varus Moment During Baseball Pitching (pubmed) which absolutely stunned me with the new methodology he had taken. Prior to that, Dr. Buffi had presented a conference paper titled Effect of Forearm Posture on the Elbow Varus Torque Generated by the Flexor Pronator Muscles: Implications for the Ulnar Collateral Ligament (pdf) which has been quoted on this blog and on my Twitter feed many times.

Dr. Buffi reached out to me not long ago and we had a great conversation where we discussed where we thought the future of baseball training would be going and where it needed to improve to make serious dents on the rash of elbow injuries that all pitchers are dealing with, from Little League to MLB. It is my pleasure to provide a platform for Dr. Buffi to present his views and to announce that he will be working with Driveline Baseball in the future in some capacity!


Challenges with Typical Biomechanical Analyses of Pitching

Have we found the Tommy John solution?

Is this the sleeve that could save baseball?

These are the questions being posed by baseball enthusiasts as the company Motus Global markets a compression sleeve that pitchers can wear to monitor and manage the workloads on their pitching elbows.

I have played baseball since I first learned to walk. I am a fanatic about the sport in every sense of the word. I also have a PhD in biomedical engineering and I can tell you that the Motus sleeve will probably not save baseball from the epidemic of elbow ulnar collateral ligament (UCL) tears that lead to Tommy John surgeries.

To be clear, I am in no way saying that the Motus sleeve is without value. From what I know, I actually think it is a solid first step. The Motus sleeve takes baseball biomechanical analyses out of the laboratory and onto the playing field in live game situations, and it provides a method for tracking your workouts and monitoring your mechanics. These are definitely good things.

However, I do have some serious questions about the claim that the Motus sleeve monitors the load on your UCL. Moreover, there are systematic challenges with the biomechanical analyses being utilized by most institutions, including the American Sports Medicine Institute (ASMI), that try to prevent UCL injuries by monitoring total elbow loading or total elbow stress.

All biomechanical analyses of pitching begin the same way. First, the pitching motion, and specifically the acceleration of the elbow, is recorded in three dimensions. This is often done using markers and cameras, or it is done using small inertial measurement units similar to the components that allow smart phones to detect landscape versus portrait mode. The Motus sleeve uses the latter approach.

After recording the motion of the pitcher’s elbow, most institutions (including Motus and ASMI) use an inverse dynamic process to then calculate the total elbow load (or stress) in the form of a joint torque. Torque is simply force that causes rotation. Calculating this total load is fairly straight forward, as Sir Isaac Newtown told us that force equals mass times acceleration. Sparing a few details, this means that the total elbow load is equal to the mass of the forearm and hand multiplied by its rotational acceleration.

Now we have come to the gaping hole in this process… how do we calculate the specific load on the UCL from the total elbow load?


The UCL is basically a tiny band that connects the humerus to the ulna, and as far as I know, it is actually impossible with existing methodologies to accurately determine UCL loading when only the total elbow load is considered. This ligament is only a few centimeters in size and it is in close proximity to many muscles and other soft tissue. It is loaded (i.e. it feels a force) when it is stretched, similar to an elastic band. The image below shows the musculature of the left forearm. The UCL is hidden beneath the highlighted muscle near the elbow.

There are more than 10 muscles that cross the elbow [1], and when we only consider the total elbow load, we really have no way of calculating how any of these muscles are individually affecting the load on the UCL during a pitch. Scientists have used experiments in cadavers to show that the muscles on the inside of the elbow (the medial side) can relieve a load on the UCL [2-4]. The problem is these experiments cannot yet be replicated in living subjects.

Additionally, the bones of the elbow also provide substantial stability. Back in 1983, Dr. Morrey and Dr. An reported that just the bones and the joint capsule can support upwards of 40% of an applied elbow load [5]. However, this study was also completed in cadavers and muscles were not considered because the cadavers were dissected.

Furthermore, I published an academic article in 2014 that showed via simulation that the load on the UCL can range from catastrophic to nonexistent depending on the contributions from the muscles and bones [6].

Therefore, it remains unclear how the total elbow load relates to the specific load on the UCL. For a given elbow load, the UCL load could be really high if the muscles and bones are weak, or it could be really low if the muscles and bones are strong.

Consider the following thought experiment: If you have two teams of 15 people playing tug-of-war and the only thing you can measure is the total load on the rope, are you able to determine the specific load supported by any individual person on either team?

This is an impossible task.

Now the question we must ask is: can we develop effective training plans using the measurements of elbow loading provided by the Motus sleeve and other typical biomechanical analyses?

Without more information, the answer is likely no.

If a pitcher has a higher total elbow load, but also capable muscles and bones that protect his UCL, he may be able to push himself more in his throwing program when the typical advice would be to scale back. Muscles get stronger by overloading, not underloading. If a pitcher has a lower total elbow load, but also much less capable muscles and bones, he may actually be at a higher risk for UCL injury than one would expect. In this case, the pitcher may need to reduce his workload until he strengthens his muscles, while the typical advice would be to do the opposite and ramp up throwing.

The bottom line is that the total elbow load or the total elbow stress is a very poor predictor of UCL injury risk. In fact, excessively monitoring a pitcher’s total elbow load could actually increase his injury risk. If a pitcher were to scale his workload back too much in response to elevated elbow loading, he could actually weaken his muscles and therefore increase his risk for a UCL tear and a Tommy John surgery. This means that improper use of the Motus sleeve could actually be very dangerous for baseball.

In my own biomechanical analyses of pitching, I avoid the pitfalls mentioned above by monitoring the loads on individual muscles and ligaments. I accomplish this using advanced numerical methods and an anatomically-based computer model of the human body. This approach will enable targeted training of specific muscles and more accurate assessments of UCL vulnerability.

There may not be a solution to the Tommy John epidemic just yet, but I am confident we can change this very soon with the right scientific approach.

Dr. James H. Buffi has a degree in mechanical engineering from the University of Notre Dame and a PhD in biomedical engineering from Northwestern University. His doctoral dissertation was called, “Using Biomechanical Modeling and Simulation to Calculate Potential Muscle Contributions to the Elbow Varus Moment during Baseball Pitching.”  He has also been a visiting scholar in the National Center for Simulation in Rehabilitation Research at Stanford University as well as a visiting researcher at Massachusetts General Hospital.


  1. Holzbaur, K.R.S., et al., Moment-generating capacity of upper limb muscles in healthy adults. Journal of Biomechanics, 2007. 40(11): p. 2442-2449.
  2. Lin, F., et al., Muscle contribution to elbow joint valgus stability. Journal of Shoulder and Elbow Surgery, 2007. 16(6): p. 795-802.
  3. Seiber, K., et al., The role of the elbow musculature, forearm rotation, and elbow flexion in elbow stability: an in vitro study. Journal of Shoulder and Elbow Surgery, 2009. 18(2): p. 260-8.
  4. Udall, J.H., et al., Effects of flexor-pronator muscle loading on valgus stability of the elbow with an intact, stretched, and resected medial ulnar collateral ligament. Journal of Shoulder and Elbow Surgery, 2009. 18(5): p. 773-778.
  5. Morrey, B.F. and K.N. An, Articular and Ligamentous Contributions to the Stability of the Elbow Joint. American Journal of Sports Medicine, 1983. 11(5): p. 315-319.
  6. Buffi, J.H., et al., Computing Muscle, Ligament, and Osseous Contributions to the Elbow Varus Moment During Baseball Pitching. Ann Biomed Eng, 2014.

We’ve published other articles summarizing our research, check them out here!

Comment section

  1. Bradley Thompson -

    Great stuff. It’s awesome seeing people working on this problem scientifically instead of from either a money making side (Modus sleeve) or from simple guess work (throw less throw less!). Keep up the great work!

    • drivelinekyle -

      I think the Motus Sleeve will be great. But I don’t think it’s the final answer to everything like it’s being pushed in the media. In fact, I’ve ordered three units and I’m waiting on them to ship. They promised a mid-February launch date, but I haven’t heard anything and I’ve pinged them a few times….

  2. Patrick -

    Would love to hear any recommendations in terms of exercise selection to implement in an arm care program that Dr. Buffi suggests.

  3. noothernameisleft -

    Maybe this explains why Japanese pitchers can successfully throw a lot more pitches in a game. Its’ training their muscle more; it would be an interesting study comparing the two countries.

    I personally believe most of the arm problems occur because kids suppinate their arm during release, rather than pronate. To pronate the thumb touches opposite side pocket on release is correct in the finishing position for a 4 seam fastball. To suppinate, the baby finger touching pocket and is unhealthy for developing age players.

    They and their parents and coaches think they are throwing a fast ball, but they are really throwing a type of curve. You can test this out by playing catch with a kid and watch the ball come into your glove. If it doesn’t have backspin and 12/6 rotation, (proper 4 seam fastball movement) his arm slot is wrong and most likely due to the finishing position of his hand. The sooner it’s corrected the better for both arm care health and accuracy in fielding plays.

    A Dad and coach of a few hundred kids over the years.

  4. Stanley Beekman -

    Thanks for the interesting article. I always enjoy reading what Biomechanical engineers write. There is something I would like to see, and that is a graph of the forces on the elbow during a pitching cycle, so a proper exercise program can be developed. The missing piece that is not discussed is the neurological component. An example of this would be if the muscle spindle cell get damaged, then the reaction time changes. This could lead to a functional weakness at a time when strength is required to off load the ulnar collateral ligament.

  5. Why Sir Isaac Newton is Still the Foremost Expert in Pitching Biomechanics - Driveline Baseball -

    […] As I’ve said before, for a specific pitcher, it remains unclear how much force is felt specifically by the UCL during each individual pitch. Researchers have attempted to gain a better understanding of UCL loading during pitching by calculating the total force load on the elbow under a variety of conditions. They’ve done this using an approach called inverse dynamics. […]

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