WALTER, Rebecca; CARRIER, David; KIM, Hyein; Univ. of Utah: Acceleration in Dogs

An animal�s ability to accelerate rapidly is likely to play an important role in many predator-prey interactions. To better understand the mechanics of acceleration in quadrupedal mammals, gait characteristics and ground forces of dogs were analyzed during rapid accelerations. Dogs were videotaped as they made standing starts with their fore or hindlimbs on a force plate, and from one and two strides behind it. The subjects were often observed to begin accelerations by temporarily unweighting the forelimbs or throwing them forward while they flexed all four limbs and adopted a more crouched posture. This movement may serve some preparatory function. Crouching could improve the mechanical advantage for applying acceleration forces and throwing the forelimbs forward would increase the amount of joint excursion over which the limbs could apply force. After this initial maneuver, dogs either took additional steps with one or both forelimbs or proceeded directly with the hindlimb push-off. A half-bound was used for the first strides. Mean and maximum vertical forces applied by the hindlimbs increased and contact times decreased as the dogs progressed from the push-off to the first strides. The maximum accelerating forces and net fore-aft forces applied by the hindlimbs were similar between the push-off and the first accelerating strides. The lack of greater accelerating forces by the hindlimbs during push-off may have been due to frictional limitations of the carpeted trackway on which the dogs ran. Alternatively, horizontal forces could also be limited during the push-off, where vertical forces are lower, if the dogs are constrained to avoid nose-up pitching moments that could accompany a high horizontal to vertical force ratio.