Acceleration and balance in trotting dogs

TLDR

During quadrupedal trotting, diagonal limb pairs land together and simultaneously exert forces on the ground. The authors measured ground‑reaction forces on each limb with four force platforms, calculated vertical and fore‑aft impulses, and demonstrated that acceleration‑induced pitching moments redistribute vertical impulse to the hind or fore limb to maintain stability. At steady‑state trotting the forelimb carries about 60 % of the vertical impulse, matching its share of body weight, while acceleration or deceleration shifts vertical impulse to the hind or fore limb, respectively.

Abstract

ABSTRACT During quadrupedal trotting, diagonal pairs of limbs are set down in unison and exert forces on the ground simultaneously. Ground-reaction forces on individual limbs of trotting dogs were measured separately using a series of four force platforms. Vertical and fore–aft impulses were determined for each 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 accelerated or decelerated during a trotting step, the vertical impulse was redistributed to the hindlimb or forelimb, respectively. This redistribution of the vertical impulse is due to a moment exerted about the pitch axis of the body by fore–aft accelerating and decelerating forces. Vertical forces exerted by the forelimb and hindlimb resist this pitching moment, providing stability during fore–aft acceleration and deceleration.