Oh yeah, I forgot. sounds kinda weird, how can you hurt yourself so bad weightlifting that you can't play for half a year?
When you damage the nerve that tells your arm to go up, it's a problem. You can't keep the muscles in the area in shape because they don't know what to do without the nerve to tell them. The nerve has to regenerate before you can even begin to think about re-strengthen the muscles in the area. And there's very little you can do to speed up the healing of the nerve.