Meeting Abstract

17.5  Jan. 4  Effects of limb placement on the mechanics of quadrupedal arboreal locomotion LAMMERS, A.R.; Cleveland State Univ., Ohio a.Lammers13@csuohio.edu

Quadrupedal animals which frequently move on arboreal substrates face unique challenges to maintaining stability. One such challenge to overcome is the tendency to topple over the sides of the branch. Any limb contact will generate a torque (twisting moment) about the long axis of the branch (unless limb force is directed toward the center of the branch). If the reaction torque is not balanced over a stride, the animal may throw itself off one side of the branch. Previous data show that the manus and pes of many animals contact arboreal substrates on different parts of the branch cross-section. This study measures the relationship between limb placement on a simulated branch and the torque generated about the long axis of the branch. Gray short-tailed opossums and laboratory rats ran across an artificial tree branch. While these animals can readily move on branch-like surfaces, the arboreal trackway was too wide in diameter for either species� manus or pes to grip the branch. The trackways was instrumented to measure torque about the long axis of the branch and vertical, fore-aft, and mediolateral forces. High-speed video was used to determine where the manus and pes contacted the branch. Preliminary data indicate that the magnitude of the peak torque is about 1.5 times greater in forelimbs than in hindlimbs. Plots of torque vs time appeared similar to vertical force vs time in both limb pairs, even though forelimbs contacted the branch on its dorsal aspect while hindlimbs contacted the branch laterally. Thus it appears that body weight is the most important factor contributing to torque generated about the long axis of the branch. Mediolateral force, an order of magnitude less than vertical force, contributes little to this torque. Placement of the limbs on the branch may have little effect on the torque generated.