In the RKC we use the term “Packing the shoulder” quite a bit, but what does it mean?
From the RKC manual: “Packing the shoulder” refers to scapular retraction (back) and depression (down). The ability to “suck the shoulder into its socket” is very important for health and performance.
We do this by engaging the lats and other muscles surrounding the shoulder joint. “Packing the shoulder” is just an easier way to remember it and explain it to our students who may not have a background in anatomy. A simple explanation is usually the most effective.
Now, if you look at top-level presses, either overhead or bench, they naturally pack their shoulders under a heavy load (or they were coached to do so). The unskilled person will tend to shrug the shoulder up and winds up going nowhere when the load gets heavy. Most of us had to learn this skill.
Mark Toomey, SrRKC did some experimenting with a fluoroscopy, which according to Wikipedia is “ an imaging technique commonly used by physicians to obtain real-time moving images of the internal structures of a patient through the use of a fluoroscope”.
I have included a couple of videos for comparison below, and you can see in real time that the clavicle, humerus and scapular move in different ways. With the packed shoulder, the bones glide right thru the range of motion. Without it, they visibly jam into each other.
“This was shot using a piece of PVC pipe filled with expanding foam insulation sprayed inside. I took a barbell to the OR with two wheels, but the metal bar created interference with the flouro machine. Went to Home Depot, got the pipe and the foam, then taped the two 45lb plates to the bar. I wanted to really load the shoulders, but the total weight was only about 95 pounds using the pipe instead of the bar.
I was standing with the bar/pipe held at the base of my skull, behind the neck, shoulders down and scaps retracted as hard as I could. Hips were neutral.
We show this when docs say, “You should never press behind the neck.”
I agree, you never should UNTIL you’ve been taught to press properly.
Here is an overhead press with OUT scapular retraction
Here is an overhead press, but with the packed shoulder: