relationship of COG and COP during quiet stance
In the case if the COP ahead the COG (see the sketch below), a counter-clockwise moment (Ia) is present at the ankle joint, resulting in backward rotation of the trunk and the balance is regained.
In the case if the COP behind the COG, a clockwise moment is present at the ankle joint, resulting in forward rotation of the trunk and the balance may be lost and possibly fall forward.