Flow is a well documented phenomena in neuroscience/cognitive processing literature. I had to read a whole book on it when I was taking a course on brain based learning a few years ago, so we could provide appropriate learning strategies and activities that would engage kids. I remember immediately making the connection to how I felt when I was riding. I was a new rider when I was reading this stuff, and I think now, it's a lot harder for me to get that feeling. Cycling feels like hard work a lot of the time! However, I feel the flow when I finish.