Then you have never really sprinted up a steep, short- to moderate-length climb. Not accelerating, just maintaining speed as the grade increases. I don’t think there’s any way to do it without some kind of good foot retention. I guess a guy who can spin really fast could downshift and manage it, but most humans are better off upshifting, standing up, and putting into play several muscle groups, not just the same few that we use for cruising on level ground.