Meeting Abstract

112.5  Tuesday, Jan. 7 11:15  Torque production and stability during narrow branch locomotion CHADWELL, BA*; YOUNG, JW; NEOMED; NEOMED jwyoung@neomed.edu

During locomotion on narrow branches, lateral movement induces increases in the angular momentum of the center of mass (COM) that, if unchecked, will topple the animal from the branch. Grasping appendages may facilitate balance on narrow branches by allowing animals to exert opposing torques about the branch, thereby minimizing disruptive angular momentum. To investigate the relationship between torque production and stability, we collected high-speed video of two marmoset monkeys ( Callithrix jacchus, mean body mass: 392g) moving across broad (5cm diameter) and narrow (2.5cm diameter) horizontal supports. We used a custom array of 6 force poles to measure applied torques about the support, and adapted force plate ergometry methods to quantify the angular momentum of the COM. Here, we analyze a preliminary dataset of 13 strides on the broad support and 12 strides on the narrow. Preliminary data indicate that net torque across locomotor strides remains quite small (5cm mean: -0.115 Ncm; 2.5cm mean: -0.074) and does not differ between pole diameters (p=0.21). Low net torque is partially due to the cancellation of torques between the right and left limbs. On average, right- and left-side torques have opposing orientations but similar magnitudes (Right mean: 0.367 Ncm; Left mean: -0.465 Ncm), such that they are negatively correlated (rho=-0.6, p=0.028). Changes in angular momentum induced by applied torques are generally opposed to the angular momentum of the COM about the pole, and on average explain 35% of the within stride variation in COM angular momentum. Overall, these data support the assertion that grasping appendages facilitate stability by permitting arboreal animals to exert opposing torques about the branch, though other mechanisms of balance control are no doubt important as well. Supported by NSF BCS-1126790.