Riding a bike in a competitive or athletic manner demands a modicum of flexibility, core strength, and upper body strength, but does little to develop these strengths. Obviously, if one is not inclined to maintain this kind of fitness, riding a bike in this manner is not a good idea.

Regardless of how you want to tilt your upper body, maintaining a straight spine is important. Many riders, mostly men, I've observed, appear to need to curve their spines at the pelvis, shoulder, or both. I don't understand why.