A team of pathophysiologists at the University of Milan has found that climbing stairs or walking for short bursts allows people to consume 20% to 60% more energy than if they do the same activity nonstop for the same distance. In their study, published in the Proceedings of the Royal Society B, the group asked volunteers to walk on a treadmill or climb stairs while also monitoring their oxygen intake.
So, this is what cyclists do. Lots and lots of low intensity miles, to facilitate those adaptations, so that over time they put out the same power but at a much lower energy cost.
Conversely, those seeking to maintain high cardiovascular fitness must cross-train with a variety of exercises, to maintain the load on the heart a lungs .