The rotational range of motion in a shoulder joint is an important indicator of function and resilience in athletes as well as the general population. As you can see in this video, this is done by measuring how much your humerus (the upper arm bone) can rotate within its capsule in the shoulder blade. Trainers and therapists look at three measures:
- Internal rotation
- External rotation
- Total rotation (internal + external rotation)
All of these numbers are important, and tell us different things. For instance, it is normal for throwing athletes such as baseball players to have decreased internal rotation in their dominant shoulders but increased external rotation. Our bodies are highly adaptable, and the soft tissue and bones of a throwing athlete will actually adapt to the demands of throwing in order to increase external rotation. In this case, the important thing is that the total range of motion is still around 180 degrees, even with the loss of internal rotation.
With non-throwing athletes, the degree of internal rotation at each shoulder is important. A healthy shoulder will have around 70-90 degrees of internal rotation. If you see less than that, it is a strong sign that you have some issues to address and are at increased risk for pain and injury. It is a common misconception to think of the rotation of the shoulder as being controlled solely by the arm. But, keep in mind that your arm is rotating within the glenoid fossa of the shoulder blade, and your shoulder blade can move all over the place. Beyond the shoulder blade, consider the ribcage, which also moves around and can hold a wide range of positions. Your shoulder blade floats on the ribcage, which provides its base of support. Move the ribs, you move the shoulder blade. Move the shoulder blade, and you move the arm. Thus, the total range of motion available at the shoulder – and the quality of that motion – is influenced not just by the tissue quality and motor patterns at the shoulder itself, but also by the position and movement of the ribcage and shoulder blade. This is why this test can tell us so much. It’s a reflection of almost everything that’s happening in your upper body, from how you breathe to how you throw a baseball.
One issue with the shoulder rotation test is that it can be cumbersome to precisely measure the range of motion of the shoulder in each direction and to keep track of the data. It’s not just taking the measurement once that matters; it’s being able to see how those numbers shift over time. To do this with current technology, it’s necessary to either use a somewhat awkward plastic gadget called a goniometer or (as you can see in the video above) to use an electronic inclinometer. Both methods are cumbersome and add an additional layer of time, complexity, and hassle for the practitioner. From there, data tracking becomes another issue. Most practitioners either enter test data into a spreadsheet or just log it by hand in a notebook or paper file. This is another step that takes time, attention, and energy that could otherwise be spent helping people. At Cipher Skin, we build smart sensors that automate these kinds of tests.
With our Cipher Skin Arm BioSleeve, our very first application automates this shoulder rotation test so that data capture is secure, accurate, and immediate. The data is instantly captured and stored in a cloud-based database. This makes the testing process faster, easier, and more effective and enables more efficient long-term data storage.