In an issue of Cycling or The Bicycle that I have from the 1950s (not sure which - I have dozens of each) there is a nice article about "ankling," which is the act of rotating the ankles to power down through a pedal stroke by allowing the foot to bend upward and then pushing back with the toes as the pedals rise from the lowest part of the stroke. Essentially this creates a miniature circular motion with the ankles as the pivot point and the pedals mirroring that motion. I do this all the time with clips on my pedals (but no cleats) and find it to be a particularly effective way to spread the tension of pedaling during long-distance rides throughout the muscles of my legs and add a bit of force to the backstroke so as to prevent momentary lapses of power as tensions moves from one leg to the other. I am sure this technique contributes to the relative comfort I felt during a 97-mile ride at a 15mph average pace (including hills) on a high-geared 4-speed bicycle last weekend, for example.
Another, far more important thing I have been trying to do is to concentrate on using my right leg (I am left-handed and my left leg is more powerful than my right) to power through pedal strokes as willfully as I do with my left. Unconsciously I have for years allowed my left leg to bear more of the burden during my rides and although it does not necessarily cause fatigue to come on more quickly with the left, is has prevented my right leg from developing apace - which would undoubtedly allow me to ride even further and faster under whatever conditions.
-Gregory