Originally Posted by koala logs

It's actually easy once you get used to it. If I set my trainer to zero resistance and just pedal along at 120 rpm for 10 minutes or more, my heart rate doesn't go any higher than 75 bpm and my breathing doesn't feel elevated at all. It feels literally effortless like I'm doing nothing and just sitting at my chair reading a good book. But that only came after two months of progressive training for increasing cadence rpm.

Pro TT racers will often hold cadence of up to 120 rpm during races.