It's been some time since I thought of physics, but isn't that true that everytime you are riding up hill or against the wind, you are overcoming an opposing force? In that case, the forces you are creating by pedaling, in order to overcome the friction and gravity is Force=mass x acceleration. That would mean that even if you are riding at a constant speed, you are actually accelerating against decelerating forces while the mass is more or less constant. That would mean that you are actually accelerating more/less at all times. Of course these forces become much more significant when the hill is steep and/or the headwind is strong, neverheless you are constantly accelerating the bike against these decelerating forces, so that rotating mass is more significant practically at all times....