Running rules as far as energy expenditure. Cycling is a refined way to cover greater distance without the energy expenditure of running. Many of us can no longer run. Cycling allows us to get the heart rate up, feel the air, work the lungs, and then after completion of a ride sit back with a short recovery time. Experienced runners have no problem transitioning from running to cycling. As far as energy expenditure, I wish I could still run, but cycling WILL DO!
__________________
No matter where you're at... There you are... Δf:=f(1/2)-f(-1/2)