Originally Posted by jim p
To me efficency is defined as my body putting out 150 watts and 140 watts going to the rear wheel of the bike as opposed to me putting out 150 watts and 100 watts going to the rear wheel of the bike.
Think about your feet on the pedals.
With no retention system, you have to maintain light pressure on the pedal as it comes up the back side or the circle in order to maintain contact between your foot and the pedal. That's "wattage" that you have to put out that's actually working against you. Forget about pulling up on the backside, just think about being able to push down less hard on the backside.
Mini toe clips are a little bit of help. Toe clips and straps are better, but your feet can still "escape" from time to time. Clipless pedals systems work better.