Originally Posted by Speedo
=The energy that goes into spinning up a wheel, you get back; it is conserved.
I guess it depends how you define "conserved" because someone else has argued that this is not accurate. He says the bike is a conservative system, but muscles are not. Thus you lose energy every time you pedal; energy does not all of a sudden go back into your leg. The discussion is in terms of frame flex, but it does get to this issue in a roundabout way.
http://bikeforums.net/showthread.php?t=268395