The Motus sleeve and its role in injury prevention

motus sleeve 1

In 2018, 17 major league pitchers had Tommy John surgery (through 9/12), and even though this is actually down a bit from previous years (per FiveThirtyEight), this still represents more than an entire team’s worth of pitchers getting Tommy John! There are a lot of reasons for this trend, but it is safe to say that any pitcher (or position player, for that matter) with aspirations of playing at a high level should make sure they are following a training program designed to keep their arm healthy. With this in mind, I wanted to talk about how the Motus sleeve (aka, the motusTHROW sensor) is a good tool for monitoring arm stress and workload, and how it can help prevent injury when used in conjunction with a well-rounded training program.


What does the Motus sleeve tell you?

motus readout

The Motus sleeve essentially gives you four pieces of information on every throw: your arm stress (peak elbow valgus torque, in Newton-meters), arm speed (peak forearm angular velocity in rotations per minute), arm slot (angle your forearm makes with the ground at ball release in degrees, i.e., a sidearm slot is 0 degrees and a true over the top slot is 90 degrees), and shoulder rotation (angle your forearm makes with the ground at max external rotation in degrees). Aside from this, it also tracks the total number of throws on a given day, and can account for different ball weights in its calculations by “tagging” certain throws accordingly. Unfortunately, all of this data is deleted at the end of each day, unless you buy a premium analytics program called Motus dash.

The most useful metric of these four is the arm stress. Obviously, all else being equal, a higher stress throw is more dangerous than a lower stress one at the same intensity level, as a higher stress throw generally implies more torque being placed on your Ulnar Collateral Ligament, or UCL. If we make this “all else equal” assumption (which I will discuss below), then the utility of the Motus sleeve is obvious. If an athlete is complaining of medial elbow pain, he (or she) could use the Motus sleeve during a training session experiment with different cues or movement patterns, and see which ones lend themselves to lower stress readings and get rid of their elbow pain.

It is important to note in using the Motus sleeve that, for a given athlete, arm stress and velocity are usually proportional, and Driveline defines the mstress metric as (arm stress / velocity in MPH) * 100 as a way of normalizing for this. In other words, for a given athlete we would expect the mstress of a low intensity 50 MPH throw to be the same as the mstress of a higher intensity 80 MPH throw. This is useful when using the Motus sleeve at lower intensities (e.g., using it on a 70% intensity day), so that you can make sure your mstress at 70% isn’t higher than your mstress at 100%.

The other metrics have some use as well, but the one to really watch is the stress. I’ve found the arm speed metric to be useful at estimating my perceived effort on a given throw. For me, a game intensity throw recently has been in the 800-900 RPM range, so I can sort of work backwards from this and make sure that, say, a supposed “70%” throw isn’t creeping up towards that range. The arm slot metric may also be useful for some guys, although it’s important to note that this isn’t a measure of contralateral tilt or shoulder abduction, since the sensor can only measure the angle of your forearm relative to the ground, not the angle of your torso or of your forearm relative to your torso. The shoulder rotation metric also could be useful, although I haven’t looked into that one very much yet.


Limitations and issues


Likely the biggest limitation to the device is the fact that it is unable to determine how much of the total stress/torque on each throw is actually torque on the UCL, and how much is distributed throughout the surrounding musculature. For example, in this blog post on Driveline’s blog, research analyst Michael O’Connell notes how a throw with 30 Nm of torque on the UCL and 34 Nm of torque on the surrounding musculature would give the same total stress reading of 64 Nm as a throw with 20 Nm on the UCL and 44 Nm on the surrounding musculature. Of course, the second throw is preferable to the first, as the goal is ultimately to reduce the stress on the UCL, but this issue of not being able to measure that stress directly makes these two throws look identical. Because of this, looking at a stress value from a given throw with no context isn’t very useful, because it is possible for one pitcher to be completely healthy at, say, 80 Nm of stress, and another pitcher to get injured at 60 Nm.

What can be useful, however, as O’Connell points out in the same blog post, is to compare how the total stress changes under different training protocols, different drills, or in response to different cues. For example, if a pitcher has stresses around 65 Nm in a bullpen and complains of elbow pain, and he tries a certain cue or new drill to address the elbow issue, he could retest his mound stress and see if it is lower than it was before. Essentially, the value of the Motus sleeve (for right now) lies in tracking changes in stress over time and in response to different training modalities, rather than just measuring the raw stress value itself.


Another more minor issue is the fact that the Motus sleeve has to be worn exactly correctly in order to measure accurately. Basically, if the sleeve is too loose, or if the sensor is oriented incorrectly, the readings could fluctuate or just be off by a consistent amount every time. This is to be expected to some degree, given that you have a device that fits in the palm of your hand capable of calculating your arm stress, arm speed, etc., but from personal experience I’ve noticed that the stresses can vary by as much as 20 Nm if the sensor is not set up properly. This is a huge margin for error, given that most guys have stresses in the double-digit range, so make sure that your sleeve is set up properly and is not too loose (see linked article for help with this).

Overall, in spite of these issues, I would argue that the Motus sleeve is a very valuable piece of equipment, especially for guys with injury histories. As long as you use it every day, or at least during high-intensity throwing days, the objective data the sleeve gives you is very useful in my opinion. Plus, as we begin to understand more and more how the stress is distributed during a throw, the Motus sleeve will be able to tell us more and more information.


My week of training

I didn’t make a blog post corresponding to last week because we didn’t have any games after Thursday, but now that conference games are picking up, I’ll be posting one each week, and plan on posting one each week after the season ends as well. Anyways, here are my stats from last weekend:

3/22/19 vs. La Verne: 0+ IP, 0 H, 3 R, 3 ER, 3 BB, 0 K, 0 HR, 0 HBP

It was another frustrating game for me on Friday, as I ended up walking three guys (all on 3-2 counts I think) and getting pulled. It’s been a frustrating year on the whole up until now, as I know that I have some of the best stuff of anybody in the SCIAC, but I just haven’t been able to put everything together yet so far this season. That being said, we still have over half of our schedule left, and I’m not going to let myself finish the year the way that I started it. I think the issue I’ve been having mentally is focusing too internally and not focusing externally on a pitch-to-pitch basis, meaning that I am not clearing my mind before the pitch and thinking only about shoving it past the hitter.

In terms of my arm health, a positive takeaway from the game Friday was they my stresses were pretty low in the bullpen before I came into the game (I didn’t wear the Motus sleeve during the game), and my arm has been feeling solid. For reference, the bullpen readings once I got up to game intensity were about 50-55 Nm, which from past experience I’ve found to be a good benchmark to aim for. The only issue I’ve been having arm-health wise is that sometimes my Motus sleeve readings fluctuate from day-to-day, in that I’ll have days where everything feels the same mechanically, but my stresses jump a bit, and I’m still working on smoothing that out. Overall, though, the stress numbers have dropped a bit from last week, which is a good sign. I didn’t have any video from this past week, but I’ll try to get some video up here for next week’s blog post!


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