My O2.. actually with a clipless type shoe there is some constriction of your feet , because if the shoe was un constricting ,

you would pull you feet out of the shoes as you tried to unclip them, occasionally .. or while sprinting ..


sort of like a desmodromic* overhead cam , Ducati Fans , the upward and downward motion is controlled so you dont have valve float at high rpm ..


the 100 rpm spinning of the pedals is thus aided by having that tight connection of foot in shoe and shoe on pedal ..


*Desmodromic valve - Wikipedia, the free encyclopedia for non Ducati Mororbike fans.