Motus Research Part 1

As most of you know if you’ve been following me on twitter (@PitchMechanics) I’ve been releasing some research on a couple athletes I’ve been working with here in my new setup at Prime Performance. I’ve gotten some great feedback but wanted to have a central place for everyone to go back and see the data, testing methods, etc. in case anyone wants to replicate any of it themselves.

Day 1:

Testing Method: After the thrower completed a full warm-up, we began to play catch with a weighted baseball. He made 15 throws with each ball (11, 9, 7, 5oz in this order) and the Motus sensor recorded the data. The first 15 throws with the 11oz ball were “warm-up” throws while the remainder were “shuffle” throws where the pitcher did a simple shuffle into the throw, similar to how an outfielder may make a long throw.

Hypothesis and Goals of the study: My hypothesis was that as the weight of the ball DECREASED, the stress (defined by Motus as the “measure of the peak torque (Nm) placed on the UCL during the pitch near the time of maximum shoulder rotation”)  on the arm (as measured by the Motes sensor) would INCREASE. My main goal of this study was just to get a sense of baseline readings with the different weighted balls and see if any of the readings were different enough to be statistically significant. I was also curious to see if (and if so, how much) the different weights impacted arm speed, arm slot and shoulder rotation.

Results and Findings: My hypothesis was generally supported as the overall stress increased as the weight of the ball decreased. Turns out the arm stress readings were fairly equal throughout the study with only a slight increase in the average stress as the weights decreased. With the 9oz ball, the stress reading ranged between 24 and 29Nm. With the 7oz ball the range was between 25 and 32Nm and finally with the 5oz ball, the range was  27 to 35Nm.

As you can see, both the floor and the peak of the readings with each ball increased as the weight decreased. Why is that? Well, there are many theories. Here are a few links from the people at Driveline who are way smarter than me: Comparing Overload vs Underload Stress and Weighted Ball Research Supporting Their Use.

Something that was also apparent after looking at the data was the strong correlation between arm speed (green line) and shoulder rotation (red line), which isn’t all that surprising when you think about it. The more the shoulder can externally rotate/”load” the faster it should be able to internally rotate/”unload”.

My final major finding was the steady drop in arm slot (purple line) as the pitcher threw more and likely began to fatigue a bit. Most pitching coaches and gurus agree that a drop in arm slot is an indication of shoulder fatigue. After discussing with this thrower’s trainer and looking over his assessment, he already has a tight left oblique muscle. In this instance it’s entirely possible that tight left oblique caused some early fatigue and the subsequent drop in arm slot. Which lead me to our next study…which you’ll definitely want to read.

Below you’ll find pictures of the full data set. Please feel free to reach out through twitter or via email ( of you have any questions, comments, or concerns or if something else jumped out at you!


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