One of the problems with "raising the arms as if holding a ball" is that raising the arms can also raise the shoulder. Many people have very tense shoulders, so when they raise their arms they cannot just raise the arms but unconsciously and unintentionally also raise their shoulders.
A different kind of problem with "raising the arms as if holding a ball" is that some people don't have a sense or feeling in the shoulder joint to know if they are raising the arm independently of the shoulder or not.
And yet another kind of problem with "raising the arms as if holding a ball" is that some people don't have a sense or feeling in the shoulder joint to know if they are pulling the shoulders forward or not as they are raising the arms to hold the imaginary ball.
The shoulders including the upper chest and upper back area can be tricky and can take a long time to work through.
As I was reviewing my oldest Zhan Zhuang Training Journal entries, I found a few scattered references to the shoulder exercises I was doing back in 1999-2000 to help me with the above mentioned problems. I thought pulling these notes together would make a nice post.
What is interesting is that even after years of doing Tai-chi, after years of doing what I thought was relaxing, I still needed to relax further and deeper! Such is the level of relaxation that can be discovered while doing zhan zhuang!
So here we go...
One purpose of this exercise might be to discover how to relax your shoulder when your arm is raising. Another purpose might be to discover that the shoulder and arm can move independently. Another purpose might be to feel deeper into the shoulder (as you shift or step forward and backward) while raising and lowering the arm.
After a hundred repetitions of this over many days, then slowly seek to find what muscles are minimally needed to lift one hand off the swing at various points in the swing arc while keeping the shoulder relaxed. Slowly wean yourself from the swing.
Of course, in zhan zhuang we are looking to feel connectedness. However, sometimes it helps to temporarily focus on an isolated area to resolve a "sticky point" in that area. Sometimes the shoulders and shoulder area can be a really big "sticky point" and may take more work than this simple exercise to resolve.
Well, there you have it. This helped me feel a little bit more into my shoulder. And of course, there are other exercises but this is pretty much where and how I started. Hope this helps you as well. Happy practicing!