We did 51 miles yesterday. My legs were fine and I could have done another 25. The pain was in my neck and shoulders. My deltoids got very tired and sore, and my neck got pretty stiff too. My deltoid endurance has gotten better this year, but I was still pretty darn tired at the end of the ride. Is it possible my handlebar is the incorrect width, or is this stricty a problem with my riding form and muscle stamina?