Right now, notice where your head is in space. Is it out forward over your chest, or is it more directly up and over your shoulders?
If not,then,as if someone pulled a thread from the top of your skullcap straight up...pullyour head up-
Doing this a little each day will loosen your back muscles & arm muscles a bit. (might even help with pain)
I bet you're nearsighted & put your head down to the screen when you read, just like me.
Now, about those arms-
I hold my pencil and mouse tight. Death grip. Been working on loosening for years.
I rest by not using either.
Turns out, touch screening a phone, uses the same death poke, and the arm up in the same tightly bent position.
Check how you're doing it
If any of you find an answer, let me know!
Take care of yourselves out there!