Meeting Abstract
8.8 Jan. 4 Quadrupedal walking, trotting, and galloping reveal different collisional patterns as assessed by center of mass velocity and whole-body ground reaction force vectors LEE, David V.; Harvard University dvlee1@gmail.com
The collisional perspective of Ruina, Bertram, and Srinivasan (2005) demonstrates that energetic losses can be reduced by employing several, sequenced collisions, instead of just one, to redirect the center of mass during legged locomotion. As they discuss, this fundamental mechanical observation holds important implications for quadrupedal gait. Here, collisional patterns of different gaits were tested experimentally in both dogs and goats. A series of four force platforms measured all of the foot forces during a stride of walking, trotting, or galloping. These individual forces were summed to determine the total ground reaction force (GRF) vector. Hence, multiple, overlapping footfalls were considered a single collision. Motion capture was used to measure the animal�s velocity immediately preceding the first footfall of the stride and this initial velocity, along with CoM acceleration measured from the force platforms, was used to determine the center of mass (CoM) velocity vector. A perpendicular relationship between the CoM velocity vector and the total GRF vector would minimize collisional loss, so the deviation of these two vectors from perpendicular, termed �collision angle�, was used to characterize differences between gaits. Collision angle was least in walking, intermediate in galloping and greatest in trotting. Velocity angles were greatest in walking and trotting, whereas, GRF angles were greatest in trotting and galloping. During walking and galloping, collision angle was significantly less than the sum of velocity and GRF angles but collision angle was similar to this sum during trotting. Together, these results suggest a collision reduction strategy in walking and galloping, where footfalls tend to be out of phase, but greater, unmitigated collisions in trotting.
