My arm and shoulder numbness went away when I got my fit adjusted so that I wasn't putting so much weight on my wrists. The backpack might be contributing to that, or maybe it is a fit issue. The solutions for me were to be able to sit more upright, with my arms a little closer together, and my hands closer to me, ie Woman Specific Design mainly. I took it further though and also got a higher stem and a handlebar that could be tilted up a bit so that it is even closer to me.