What the muscles do
A muscle can only pull. Shorten it to see what it moves.
A model, not an atlas: the muscle shapes come from real 3D meshes, fitted to a figure with the measurements of ANSUR II; joint limits from the usual norms (AAOS), the limits of the hamstrings, the front of the thigh and the calf from Kendall's length tests.
Shapes of muscles and bones: BodyParts3D, © The Database Center for Life Science, CC BY 4.0, fitted to the figure and simplified.