Turning the Corner in Quadrupedal Arboreal Locomotion: Kinetics of Changing Direction While Running in the Siberian Chipmunk (Tamias sibiricus)

Abstract

Arboreal animals frequently change directions during locomotion on tree branches, trunks, or twigs. Linear and rotational impulses required to change direction and rotate the body while running are largely unexplored. We trained Siberian chipmunks (Tamias sibiricus) to run on narrow cylindrical trackways. The first trackway was straight and the second had a 45° bend to the right. A force pole collected substrate reaction forces and torques, and linear and rotational impulses were calculated. When the chipmunks ran and jumped across the bend, they exerted strong impulses to the left, pushing the body to the right. Before the bend the substrate reaction yaw angular impulse rotated the animal to the new heading. After passing over the 45° bend in the trackway, opposing yaw angular impulses were exerted to stop the body's rotation. Rolling angular impulses were mostly similar between straight and turning trials. We conclude that mediolateral forces are more important than craniocaudal forces to change direction in locomotion. Yaw angular impulse is necessary to start and stop the rotation of the body around the center of mass. To avoid rolling during turns, the chipmunks relied on banking rather than exerting rolling torques.