Acceleration and balance in trotting dogs

During quadrupedal trotting, diagonal pairs of limbs are set down in unison and exert forces on the ground simultaneously. Ground-reaction forces on i ndividual limbs of trotting dogs were measured separately using a series of four force platforms. Vertical and fore-aft impulses were determined for e ach limb from the force/time recordings. When mean fore-aft acceleration of the body was zero in a given trotting step (steady state), the fraction of vertical impulse on the forelimb was equal to the fraction of body weight supported by the forelimbs during standing (approximately 60%). When dogs a ccelerated or decelerated during a trotting step, the vertical impulse was redistributed to the hindlimb or forelimb, respectively. This redistributio n of the vertical impulse is due to a moment exerted about the pitch axis o f the body by fore-aft accelerating and decelerating forces. Vertical force s exerted by the forelimb and hindlimb resist this pitching moment, providi ng stability during fore-aft acceleration and deceleration.