Try this exercise if you want to improve these two important factors for healthy shoulders:
Thoracic Spine Mobility
The arms alternating overhead is an example of a reciprocal movement, which creates a push-pull effect on the thoracic spine in the frontal plane.
The thoracic spine needs to be mobile in ALL planes of motion, not just extension, although extension is probably the most important to focus on for most, so this is a great drill to hit something that’s neglected.
When the arm is up overhead and you’re activating the upper trap to shrug the shoulder and reach the arm out and away from your body, the muscles that connect the scapula to the thoracic spine are pulling the thoracic spine up and away (superolaterally), opening up the space on the same side of the spine.
With the arm down low, you’re firing the muscles that retract and depress the scapula like the lower trap and rhomboid minor, which will pull the thoracic spine downwards. This closes the space down on this side.
Here’s a graphic I created to help illustrate this concept (reminder I am not a graphic designer):
So when you go back and forth, you’re essentially “pumping” the thoracic spine and motion is what helps the spinal structures like the discs stay healthy because it helps stimulate blood flow into and out of the tissues.
Remember – it’s not the size of the boat but the motion in the ocean.
Oh wait, that’s something else. Nevermind.
Overhead Shoulder Mobility
Most of us need to continue working on our overhead shoulder mobility, simply because everyday life works to make it worse.
So whenever we get a chance to do a drill that helps improve it, especially when it helps improve other important areas of the body (thoracic spine), it’s a good drill to do!
Now you’ve got the background – here’s the technique:
I suggest you start off with something like 2 sets of 6 reps per, with a 5 second hold. Progress to longer holds and always focus on QUALITY vs. quantity.
If you’ve got shoulder issues, you may need more than just a single technique because it’s such a complex joint, so I suggest you check out the Scap Control course if you’re serious about fixing your problems for good.