OK, what I think he means is that the muscle on his right arm is weakened and smaller. What you have to do is, concentrate more on your right arm. Make sure to start slow, and don't push it to the point where it breaks again (lol.) Ask your doctor if it's alright to do weight lifting, because I know I broke my arm right before summer, and when I got it off, my right arm was considerably smaller than my left, now my right arm is bigger.