Thread by @BaseballFreak_9

BIOMECHANICS THREAD (long one, strap in):

Integrating assessment data into programming and using retest data to make sure we're on the right track: Changing Shoulder Abduction.

From a blog that @Bryan__Leslie and I wrote (edited by @OC____ ):

drivelinebaseball.com/2018/12/changi…

Within the biomechanics reports, we obtain various kinematic metrics of the upper and lower body during the throwing motion.

Today, we're going to focus on shoulder abduction, a primary metric for arm path. The angle between the humerus and the torso in the frontal plane.

We’ve seen, on average, elite throwers are more consistent with their shoulder abduction from front-foot contact through ball release—almost as if their elbows and shoulders rotate on the same plane as one another.

Here's Page 2 of our report with the upper body kinematic positions. Shoulder abduction is highlighted in the table (red box), and the path the angle follows from foot contact to ball release is the purple line on the graph.

This athlete has a consistent path around 90 deg 🔥

Biomechanically, it makes sense that we would want to have consistent movement in this plane. During the arm action, the humerus will already have to move through the transverse plane (shoulder horizontal abduction), out of scap load, and into release.

Additionally, the fastest movement in sports will be occurring at this joint through the internal rotation of the humerus, at speeds upwards of 6,000 deg/sec. Extra movement of the humerus at the level of the shoulder could possibly create inefficiencies and unwanted stress.

IMPORTANT NOTE: Not all arm paths are equal. Not everyone needs to subscribe to this idea of shoulder abduction being at 90 degrees from foot contact to ball release. This is a general observation, and ultimately everyone throws a little differently.

The Assessment:

Here’s a great example of an athlete that we have assessment and retest data on who needed to make a similar change. When he showed up, we deemed that his shoulder abduction path “had room to improve.”

Did ya see it? It’s right there. Here let’s try a different view, maybe that’ll help.

How about now? No? To be honest, neither did I, and I spend everyday looking at these images.

But when we look at the data for the shoulder abduction path, It’s pretty clear that the path of the humerus is inefficient with room to improve. A great example of how the biomechanics report can provide objective data that we otherwise would have missed.

Report notes ⬇️⬇️⬇️

- The arm starts almost 19 degs above 90 at foot contact
- drops down below 90 to about 87 degs
- then comes back up to 107 degs by ball release.

That’s quite a bit of unnecessary movement around an axis that we’d like to see stay more consistent.

This was noted in the athlete’s training profile:

“Shoulder abduction at ball release is pretty high , so really make sure to keep an eye on your arm path and make sure that your aren't exaggerating the elbow spiral. Pivot pickoffs are going to be the best drill to feel that.”

The Retest:

Data means nothing if we don’t monitor and then retest. So a few months later, following an emphasis on arm action and arm path, we re-tested this athlete in the biomechanics lab. It doesn’t look like much, but we made pretty significant changes.

Again, it’s hard to tell in the video, but the report is able to fill in the rest of the story:

That’s a pretty clean arm action. You can see the purple line of shoulder abduction staying fairly consistent at around 90 degrees from foot contact through ball release

Here’s another view where I’ve overlayed the assessment and retest data. The assessment data will remain in color while the retest data is now black.

A few important things to note from this overlay: ⬇️⬇️

- Cleaner abduction path (purple)
- Maintaining a good amount of shoulder horizontal abduction/scap load (red line).
- Achieving significantly more maximum external rotation (MER). It’s possible that this new abduction position allowed the athlete to achieve greater MER.

Additionally, this athlete gained 5 mph from his assessment mound velocity (84 mph) to his exit mound velo session (89 mph). While also maintaining a low Max Varus moment from assessment (74 Nm) to retest (80 Nm).

Let’s see what the overlay looks like when we compare the motion capture of both reports:

Red: assessment
Green: retest

Again, it’s hard to see much, but here are some notes: ⬇️

- It doesn’t appear that the retest elbow is that much “lower” which means that trunk positioning and tilt are heavily influencing shoulder abduction angle.
- Greater maximum external rotation could be related to this more efficient abduction path.

A closer look at that MER change

Even if it’s just for a few frames, you can see the arm resting a little deeper into lay back which could have larger implications for velocity and stress reduction that we're (mainly our Romanian super-computer @Alex_Caravan) still looking into!