腰不動,足不發
The feet do not emit if the waist doesn't move.
勁從足下起,還得丹田足
The strength rises from the feet on the prerequisite the cinnabar field is full.
For internal practices, roots are an active relationship between the feet and the waist. Hence, moving the whole body while keeping the feet still is a way to work and enhance such relationship. Semi-static postures in the three-steps training were paying special attention to two things, keeping the feet as still as possible and the pelvis as straight as possible.