I have been playing the piano off and off for a couple of years now. I just recently started practicing again since I'm out of school for the summer. I've been practicing diligently for a couple of weeks, but I've found that when I practice, I get tension at my wrists, and on a couple of muscles in my forearms. My arms are very skinny and aren't that strong. The tension in my wrists is usually felt after I'm done playing and I turn my palms upward. I never feel any sharp or shooting pains, so I know it's not carpel tunnel. Do I have to watch out for tendonitis? Or could it be that I've been away from the piano for sixth or so months, and my muscles that have normally been used are out of shape? I also have pains in my upper back muscles from moving my arms briskly, like I've pulled them, but I know that's going to go away soon. That's normal for me. Again, it's only in my wrists and a couple of muscles in each of my forearms.
The most demanding piece that I've been playing is Albert Elmenreich's Spinning Song, and my arms/wrists first ached after playing it for 45 minutes straight (when I was learning it, which was at a very rapid rate). After I had learned almost all of it, except the middle section, my arms at wrists began to hurt a little bit less. If they ever did ache, I would just practice the middle section very slowly to ward off any tension. Now, having learned it, I can usually play it about 8 or 9 times before any muscle tension seems to occur in either my wrists or forearms, and that's usually if I don't play anything else. Any thoughts?