Originally Posted by
Bacciagalupe
That doesn't mean you are actually applying usable force to the drivetrain. It doesn't take a lot of force to create that sensation / subjective impression.
The amount of power that actually makes it to the drivetrain in those situations is negligible.
Basically, they put pro cyclists into stationary bikes with pedal-based power meters, instruct them to pedal in different fashions, and measure the output. E.g.
http://www.ncbi.nlm.nih.gov/pubmed/17545890
And for bonus points, this is some raw data from Metrigear's pedal-based power meters, which show what's actually happening when you're pedaling. The right leg applies force on the downstroke; the amount of power drops to zero; and then it climbs again. When the right leg is at the 12:00 and the left leg is at the 6:00, that's the "dead spot." It only
looks like continuous force is applied to the drivetrain when you average it out.
I.e. your legs are not supplying continuous power to the bicycle. A bicycle is a two-stroke engine, and foot retention doesn't change that.
No one is saying clipless pedals magically give you continuous power, that's just silly. These graphs are exactly what I would expect for steady state cruising along with or without clipless pedals. I do notice a bit of negative values, especially on the right foot. Its small, but I wouldn't call that insignificant. The fact that you can unweight your pedal completely without your foot floating off is also very significant for power production.
I completely agree with their conclusion - that pedaling technique is not that significant to power output. Notice their conclusions mention nothing comparing to platforms, sprinting or climbing a steep hill. Is there a graph showing power output on platforms? I find when I am on platforms that I never fully unload the upstroke pedal, and my feet start hurting a lot quicker.