When animals travel on tree branches, avoiding falls is of paramount importance. Animals swiftly running on a narrow branch must rely on movement to create stability rather than on static methods. We examined how Siberian chipmunks (Tamias sibiricus) remain stable while running on a narrow tree branch trackway. We examined the pitch, yaw, and rolling torques around the center of mass, and hypothesized that within a stride, any angular impulse (torque during step time) acting on the center of mass would be canceled out by an equal and opposite angular impulse. Three chipmunks were videotaped while running on a 2 cm diameter branch trackway. We digitized the videos to estimate center of mass and center of pressure positions throughout the stride. A short region of the trackway was instrumented to measure components of the substrate reaction force. We found that positive and negative pitch angular impulse was by far the greatest in magnitude. The anterior body was pushed dorsally (upward) when the forelimbs landed simultaneously, and then the body pitched in the opposite direction as both hindlimbs simultaneously made contact. There was no considerable difference between yaw and rolling angular impulses, both of which were small and equal between fore- and hindlimbs. Net angular impulses around all three axes were usually greater than or less than zero (not balanced). We conclude that the chipmunks may balance out the torques acting on the center of mass over the course of two or more strides, rather than one stride as we hypothesized.
Lammers, Andrew R. and Zurcher, Ulrich, "Torque Around the Center of Mass: Dynamic Stability During Quadrupedal Arboreal Locomotion in the Siberian Chipmunk (Tamias sibiricus)" (2011). Physics Faculty Publications. 281.
NOTICE: this is the author’s version of a work that was accepted for publication in Zoology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Zoology, 114, 2, April 2011 DOI#10.1016/j.zool.2010.11.004