Meeting Abstract

79.3  Friday, Jan. 6  Dynamic stability during quadrupedal arboreal locomotion: Body segment contributions to angular momentum LAMMERS, A. R.*; ZURCHER, U.; School of Health Sciences, Cleveland State University; Department of Physics, Cleveland State University

Traveling on narrow tree branches and twigs presents a challenge to maintaining balance and avoiding falls. To remain stable while running quickly on an arboreal support, animals may rely less on static stability (increased duty factor, modified limb phase, crouched posture, etc.) and more on dynamic stability, which results from movement. We examined angular momentum in the trunk and head, forelimbs, and hindlimbs of Siberian chipmunks (Tamias sibiricus) running on a cylindrical trackway about half the diameter of the chipmunks’ torso. We marked body segments on the chipmunks’ fur using white paint, and videotaped the running animals using two 210 Hz video cameras. By digitizing the two videos, we assembled a set of 13 three-dimensional points representing the head, segments of the torso, the tail, and the right forelimb and hindlimb. Using body segment masses obtained from a cadaveric specimen, and the linear and angular velocities of the three-dimensional coordinates, we calculated linear and angular momentum of the entire body, and of the torso/head segment, tail, right forelimb, and right hindlimb. Preliminary data show that fore-aft linear momentum was far greater than vertical, and mediolateral linear momentum fluctuated around zero. Rolling angular momentum also fluctuated around zero for all body segments; yaw angular momentum also fluctuated around zero, but there were relatively large moments when the forelimb or hindlimb lifted off. Pitch angular momentum was considerable, and the forelimb and hindlimb each contributed about twice the angular momentum of the torso. Because a non-zero pitch angular momentum makes falling of the sides of the branch less likely, we conclude that limb movement plays a major role in maintaining dynamic stability during fast arboreal locomotion.