The purpose of this study was to investigate the determinants of postu
ral orientation by examining stance kinematics and kinetics at various
interpaw distances. Four adult cats were trained to stand, unrestrain
ed, on a force platform. Three-dimensional ground reaction forces and
kinematics, as well as EMG activities, were recorded during stance at
five different anteroposterior (AP) distances and two widths. Stance d
istance was varied by changing the distance between the four force pla
tes mounted on the platform. All cats used a strategy of maintaining a
constant horizontal orientation of the trunk and levering the limbs a
t the girdles while maintaining constant intralimb geometry to accommo
date the changes in stance distance. The direction of the ground react
ion forces covaried with the limb axes. As a result, the joint torques
were conserved in the forelimb, and varied within small ranges in the
hind. Increased tonic activity in the extensors of the back, the hip,
and the ankle was observed at shorter distances while increased knee
extensor activity was observed at longer distances. A cost function, d
efined as the sum of squared 3-D joint torques, was minimal for the hi
ndlimb at a stance distance which corresponded to the preferred distan
ce naturally assumed by each cat on the floor. Thus, in the maintenanc
e of stance posture, trunk orientation and intralimb geometry is const
rained, the goal of which is to minimize muscular effort or energy exp
enditure.