Originally Posted by Carbonfiberboy

Steady power is really easy on the trainer. It's way harder out on the road. It's not that cadence is varying so much as it is that force is varying. We seem to have pretty good speed sensors in our legs. Micro variations in road grade and wind cause us to increase force in order to maintain speed and cadence. Possibly that is more evident in those of us who have practiced holding a steady pace. Riding a paceline, nothing is more frustrating than a lead rider who doesn't hold steady. I admit to being shocked at the power variations at a steady speed and cadence when I first went out with a PM, which was after weeks of roller work with that bike and PM.

I would also like to stress that everything that we see on our HRMs is relevant to training. The variations do take a lot more experience to interpret than does power, but that doesn't change their relevance. They only seem random if one doesn't understand what's going on.