This is such an amazing thread.. never have I thought about the impact of the position we ride in, and how the handlebars effect our comfort. With our arms low, as soon as they extend, the rotator cuff is recruited (may or may not feel uncomfortable right away - there are 4 muscles around / behind the shoulder), which will eventually fatigue, and put a lot of pressure on the rhomboids (diamond shaped muscle in the middle of the upper back). Since this affects a lot of structures on / around the spine, you can then start to get continued fatigue (muscle fatigue runs up the body), and a pinched nerve in the upper back or lower neck when things start to go out of alignment, and a nerve is impinged (pinched) between a muscle and something else (kind of like the pain you get in your balls sometimes - usually more the right one than the left - that comes and goes when your piriformis muscle is acting up, and you think you have testicle cancer... has anyone ever experienced this?). I love this stuff... and thank god I finally have a use for 4 years in med school!