Is the limb axis, with respect to t

Is the limb axis, with respect to the vertical, the geometrical
reference value which is regulated during stance? An alternative explanation has been proposed
by Macpherson and by Fung and Macpherson
[PI. By changing the interlimb distance in the sagittal
and frontal plane, they concluded that the length
and the orientation of the trunk with respect to the
supporting surface, i.e. an external reference frame, is actually
regulated, the legs being used as levers to maintain
the trunk length constant, while the interlimb distance
is varied. These authors concluded that the preferred interlimb
distance during natural stance corresponds to the
distance involving the least energy consumption.