Most people assume the pedal stroke is natural, or they somehow already have the skill set to pedal efficiently. The vector chart below is a pretty common picture of what that assumption leads to.
In order to power a bike efficiently you must push the pedal in the direction it’s going – pushing down at the bottom does no good at all, keeping weight on the pedal at the back of the pedal stroke subtracts power.
To build a good pedal stroke you must first identify the motors being used and how they work – the body is a bunch of pivots which dictate which direction any given muscle is able to apply force. Here are the muscles and pivots we’re working with:
Glutes extend the femur down from the hip.
Quads extend the tibia from the knee.
Hip flexors lift the femur from the hip.
Hamstrings draw the tibia back from the knee.
Learning how to create a force vector
You thought this was easy?
What this is showing us is that pushing in the direction the pedal is going at any given point in the pedal stroke is the sum of two force vectors (two muscles working). In this example the glutes supply downward force while the quads supply the forward force to add up to the 60 degree force angle.
The whole [ideal] pedal stroke
This is an ideal case, ignoring that some muscles are larger than others. The truth is that there will be zones where large muscle groups have mechanical advantage and zones where they don’t. We will be focusing on where the two larger muscle groups can work (glutes & quads).