Low frequency vibrations by human body locomotion during stance phases on one leg, and their analyses, must be related to the joints of the leg. Especially the ankle shows cardan joint properties, causing inversion of the foot before toe-off. Inversion is turning the footsole inwards, eversion is turning it outwards. This foot inversion was determined by means of anatomical specimens, using modern imaging techniques. Mean value of about 9° inversion prior to toe-off corresponds with in vivo measurements from literature. Comparative observations in the hind limb of the opossum, a primate predecessor, reveal essential differences regarding lower leg coupling mechanisms.