Probably the easiest solution is to change the parent of the feet from the figure body to the ground plane. Select foot, Object > Change Parent... Select ground plane, [OK]. Repeat for other foot. This will keep the foot from reacting to movements of the models body. You can use the graph tool to eliminate all movement in the foot during ground contact. ([ctl]+[shift]+G) Also dont forget to add keys to all elements at every key frame or strange things may happen. Also as you animate your sequence be sure to look backward periodocially to make sure no strange ness is happening.