I'm seeing a physical therapist right now for some shoulder problems (basically, my ligaments are too lose and my rotator cuff isn't strong enough). The first time I went I asked if cycling was still allowed and she said aerobars would be my best bet becasue being in that position would encourage co-contraction of all the supporting shoulder muscles and would be like strengthening without realizing it. She didn't think that being upright (hand on the flat part of the handlebars as opposed to in the drops) was a very good idea. I haven't been able to get aerobars for financial reasons, but staying in the drops seems to have helped a bit.