Interaction between motion of the trunk and the angle of attack of the forelimbs in synchronous gaits of the pika (ochotona rufescens)

Abstract : During half-bound gait on a treadmill pikas (Ochotona rufescens: Lagomorpha) show a preference in the choice of the trailing limb (“handedness”). Duration of steps shows significantly higher variation in the trailing limb than in the leading limb. This observation motivated calculations of the position of the center of mass (CoM) in the body frame of the pika during half-bound cycles. CoM is aligned with first of the ulna of the trailing and second of the leading limb during major parts of the forelimbs’ stance phase. Referring to our large cineradiographic data base on the kinematics of the legs we could note that the horizontal motion of the CoM in the body is mainly determined by flexion and extension of the back. This observation underlines the determinant role of the trunk as the main engine for fast locomotion. Using high-speed video films we measured the angle of attack (defined as the angle between the ulna and the ground at touch down). We couldn’t observe any significant change with speed during half-bound, indicating the important role of self-stabilising mechanisms on the choice of kinematics.