I didn't much get what you meant.
Could you explain it a bit more?

Foot-to-leg pathing is a ♥♥♥♥.
Essentially, you give it two coordinates - one where the foot starts (when the leg is as contracted as possible), and one where the foot ends (when the leg is as extended as possible). The foot slides in a straight line from point A to B as the frames cycle. So if your sprites don't have the ankle moving in a straight line at an even speed, you're going to have problems.