Fig. 1.
Determining static and dynamic stability of locomotion. A: frontal view of the cat demonstrating unconstrained and narrow path walking conditions. Gray and open squares indicate estimated centers of the joints or paws. Angle q is the hip and shoulder angle in the frontal plane. B: perspective view of the cat during walking and definition of the hindlimb plane (the forelimb plane was defined in the same way). Three open markers on each limb were used to define unit vectors v, u, and w and the limb plane (see text for further explanations). C: dorsal view of the cat during walking: black-and-white circle, center of mass (CoM); black-and-white diamond, extrapolated center of mass (XCoM) position. Paw prints indicate paws on the ground that form the base of support, a lighter gray area. Filled circles are markers on iliac crests, scapulars, at the corner of each eye and ear. D: definitions of the base of support, index of static stability (ISS), index of dynamic stability (IDS), and its components, i.e., index of dynamic stability in the frontal plane (IDSf) and index of dynamic stability in the sagittal plane (IDSs) (see text for further explanations).