The best way to explain the most efficient pedal stroke is through this clock diagram (below). I'll start with 12 o'clock. At the top of the pedal stroke your foot should be at the same position as it is at 6 & 9 o'clock. That is, the heel should be slightly elevated from the toe. Your hip extensors or glutes are ready to kick in and drive the foot forward at the top. At this position you'll feel the toes hitting the fronts of your shoes. At 1 o'clock, your knee extensors, or quads, are ready to kick in and supplement the glutes. The 2 o'clock position is the position of max power applied to the pedal because your glutes and quads (the biggest muscles) are both fully engaged. Your heel will drop down from its elevated position so that your foot is horizontal to the ground. At the 3 o'clock position your foot will be horizontal and your heel may drop slightly below the toe level depending on the grade and/or how hard you're pedaling. At the 4 o'clock position your glutes will acquiesce and let the quads takeover. At 5 o'clock, or bottom of the stroke, your calves kick-in and takeover for the quads. At 6-7 o'clock, your ankle dorsiflexor or shin muscles kick-in. At this point you should feel like you're scraping mud from the bottoms of your shoes. The hamstrings do all the work from 8-9 o'clock. At this point you're actually pulling up slightly on the pedal (a lot if you're climbing). You may not feel it but you are. At 10 o'clock through 12 o'clock it's all hip flexor. Again, you're pulling up slightly on the pedal.
Notice the foot position on the pedal is just about the same at the 6, 9 and 12 o'clock position. Also, notice when pedaling correctly you're utilizing ALL of your leg muscles- front and back including the glutes. You want good balance. i.e. you don't want strong quads and weak hamstrings or glutes. You want everything strong.
The Winter months are the months you want to work on pedaling efficiency. One leg pedaling drills are probably a good idea to inject into your winter training plan/workouts. You'll know if you have a good pedal stroke if it isn't jerky or erratic. If it is, work on being smooth throughout the entire clock.
Check out the photo of Bradley Wiggins below. Notice the foot position at 12 o'clock and 6 o'clock. i.e. heel slightly elevated. That's what I'm talking about.
Power ON! Coach Rob