With your arm resting at your side, raise it up over your head.---
Now try and see if you can use the triceps, and the area underneath the armpit while relaxing and not activating the shoulder.
I've been trying this for a few minutes only, but I can't do it. I'm usually pretty good at figuring these things out, and I'll keep trying.
But by thinking about how my muscles work, I can't figure out how I can raise my arm like this, and not activate the shoulder. Because muscles only contract, I can't figure out how the muscles below my arm can raise my arm. When holding weight, I can activate my lat for more support, but there is no doubt, when I try it, that my shoulder has to activate.
Can you (or anyone) make a video of this, so we can see the shoulder muscles? If I touch my shoulder, I keep feeling it activate when I raise my arm.