Animation drawings of walks and runs, from Richard Williams survival guide

 this was helpful for me to understand the structure of a walk cycle. Looking at the bottom drawing the pelvis shows the body, with inertia downwards force demonstrated through arrows.  the movement goes up in multiples of 6  starting from zero so the next step will be six, then 12 then 18 then 24, Working with 24 frames per second which is what most film companies use.