Again..we should appreciate the 'system' and try to tune each component of the system. Power and body mass(power to weight ratio) is very important to that system(this ric and I agree)...but this is just one part of the system dynamics. When you tune the entire system..you become a more effecient/economical cyclist. I consider technique, balance, and elegance a part of that system.as well as genetic factors. mental factors, tactics, explosiveness, physiological factors, etc. Economy/effeciency is essentially the art and science of knowing the importance of the system approach...and training and tuning the system..and further..putting it into practice on the open roads...and managing it under race conditions in a way that makes the most of your power(neuro muscular) and cardio/vascular/respiratory fitness level.