When I ride for more than about 30-40 miles I get a really bad muscle pain in the middle of my upper back, between my shoulder blades. I can't determine if it is just from lifting my head up to look forward (just neck pain extending on down into the upper back) or if it is from my having my shoulders tense and pulled up and back. I try to relax my upper body as much as I can, but I still have problems with this. On 60-70+ mile rides it gets unbearable. Does anyone else have this problem?