I have noticed that when I ride for a long time (up to an hour) I get a sharp pain behind my left shoulder. It is really sharp, like a tight knot in my back. I wonder about it too. Is it something I just have to get used to? It doesn't feel like regular muscle soreness. I try and change positions, like riding with my hands close together in the middle of the handle bars, but I have a mountain bike and it is terribly dangerous to steer like that. I kinda want to get a road bike with the handle bars that keep your hands close together (therefore stretching out your back, which I think would be the cure), but I don't have any extra money right now. I would like someone who knows to respond.