Meeting Abstract

74.6  Tuesday, Jan. 6  Mechanical Differences between Trotting and Galloping in Quadrupeds ROS, Ivo G*; BIEWENER, Andrew A; LEE, David V; ANTONEN, Jennifer; HIGGINS, Trevor; Harvard U.; Harvard U.; UNLV; Harvard U.; Harvard U. ivo.ros@gmail.com

It is generally believed that quadrupeds transition from a trot to a gallop to reduce peak forces and galloping is energetically advantageous to trotting at higher speeds. To enhance our understanding of the underlying mechanics, we contrasted the interactions of the whole body ground reaction force (GRF) and the center of mass (CoM) between trotting and galloping. Goats and dogs steadily galloped and trotted over four adjacent force platforms while 3D body and limb kinematics were recorded simultaneously. In trots the GRF tightly tracks the CoM throughout the stride. As predicted by the theoretical spring-loaded inverted pendulum (SLIP) model, this leads to greater fluctuations of the horizontal translational kinetic energy (KE) and CoM trajectory compared with galloping. In contrast, during galloping GRFs of the fore and hind legs act in front of and behind the CoM respectively, producing torques about the CoM that add rotational KE to the body. This results in oscillating pitch rotations, or rotational KE fluctuations. As a consequence, galloping goats and dogs travel with a more uniform horizontal KE, flatter CoM trajectories and lower, more vertically oriented GRFs than would be expected for trots at similar speeds. Our results therefore indicate that switching from a trot to a gallop lowers peak forces by reducing the vertical GRF component, applying less work to the CoM. (Supported by DARPA Biodynotics)