For kicks and giggles sometime, try tightening the muscles of the forearm/wrist and shoulder while relaxing the muscles around the elbow. It's entirely possible to do, but until your cerebellum figures it out, you can wish all you want to do this seemingly simple task. When you try to relax your arm above the elbow, I guarantee you'll relax the muscles of the shoulder and wrist, at least if this is the first time you've tried this.
Intellectualization is great, but words are words.
I was taught early on in my aikido training about relaxing various muscle groups while tightening others. The first was learning to grasp someone firmly with one hand while relaxing the rest of the body, from the elbow up through the shoulder and down through the rest of the body.