Ask the Expert: Foot position during the pedal stroke
I turned to ICA team member Tom Scotto to help me answer the question and this is what Tom said:
Tom has said he will soon write a full article on the biomechanics of the foot and optimal pedaling position.
I'll add a little more to that from what I've taught at Spinning® orientations over the years.
If you notice elite level riders, they do tend to have a toe down position. Lance Armstrong has a particularly pointed toe. But it's still not an overly exaggerated pointed toe. This foot position tends to happen naturally on its own when the bike set-up is correct and when riders have a fluid and relaxed pedal stroke without a lot of conscious thought.
Now, take a loot at a lot of novice cyclists as they pedal. Very often they point the toe down but keep it pointed throughout the entire pedal stroke. Their calf muscles are firing the entire time and the ankle joint is locked in a position of plantar-flexion. I'm not so sure why this is such a common tendency with novice riders, because it looks and feels so uncomfortable, but it really is very common. You'll notice it indoors with your newer students.
A rough rule of thumb is that too much dorsi-flexion (heel down/toe up) is often a result of the saddle being too low; too much plantar-flexion (toe down/raised heel) throughout the entire pedal stroke may be a sign of a saddle that is too high. But it's important to realize that is not always the case; sometimes you'll see the beginner cyclist push the toe down even when the saddle is too low - a very strange looking pedal stroke indeed!
The solution is to encourage your students to pedal with a fairly flat foot, allowing the ankle to articulate as needed as the leg moves through the pedal stroke. There shouldn't be a lot of thought about moving the toe up and down. Rather, think of the foot as being a firm lever (as Tom suggested) and letting the ankle joint relax so that it isn't locked, but not so much that the heel tends to drop on the downstroke or that you are consciously trying to pull the toe up on the upstroke. In the diagram above you'll see that the only time the toe is dropped relative to the lower leg is at the bottom. The rest of the time, even though the heel seems to be higher than the toe, if you look at it relative to the tibia, it is still at a 90 degree angle.