For life drawing we practised drawing feet, I was using reference drawings from Burne Hogarth – Dynamic Figure Drawing . I found their breakdown works best in a practical sense for drawing more than the other tutorials I’ve found.
Though it was harder in application , mainly when I was bending the foot with how the ball of the foot bended as well.
reference: Hogarth, B. (2008). Dynamic figure drawing. 1st ed. New York, NY: Watson-Guptill.