|Standing on tiptoe|
The drawings below also show the tension of the muscles in the leg. The first shows a man standing on tiptoe and the second a woman walking on tiptoe. You can see that in both of them the lower leg is thrust slightly forward which will cause the standing figure to lean backward slightly from the torso. The gastrocnemius muscle at the back of the calf contracts, as does the biceps femoris at the back of the thigh. These two contractions cause the knee to bend slightly when a figure either stands of walks on tiptoe.
Left, standing on tiptoe, right walking on tiptoe.
An anatomical drawing of the knee, leg and ankle on tiptoe from Cunningham's Textbook of Anatomy By Daniel John Cunningham
Comic Artist's Photo Reference - People & Poses: Book/CD Set with 1000+ Color Images (Comic Artists Reference)
More photos of people walking here.