Meeting Abstract

6.6  Friday, Jan. 4  Three-dimensional joint mechanics and kinematics of jumping lizards OLBERDING, JP*; HIGHAM, TE; Univ. of California, Riverside; Univ. of California, Riverside jolbe001@ucr.edu

Hindlimb kinematics are often examined and related to locomotor performance in lizards, but establishing a causal link between individual joint movements and whole-animal performance requires an understanding of joint mechanics. This study examines the mechanical contributions of each hindlimb joint movement and the patterns of joint mechanics that result from increased demand on the hindlimb (increased whole-animal performance) during jumping, an ecologically important form of locomotion for many species of lizards. We placed collared lizards, Crotaphytus collaris, on a custom 6-axis force plate and encouraged them to jump onto a vertical wall near the force plate. We recorded simultaneous force data and 3D high-speed video, then used inverse dynamic modeling to calculate kinematics, moments, powers, and work for the ankle, knee, and hip of one hindlimb, around each of the three axes of rotation. The correct positioning of the limbs prior to jumping was necessary to effectively generate power at the joints. Prior to jumping, the lizards took a small step forward bringing the hindlimbs into a crouched position with the feet oriented forward along the long axis of the body. A more laterally oriented foot at the start of the jump reduced the angular excursion of ankle extension resulting in a lower peak power and less work from that movement. Ankle and knee extension and femur retraction did the majority of positive work during the jump and more work was done by knee extension and femur retraction in jumps with a higher peak COM velocity. Increasing the angle of the body relative to horizontal at takeoff decreased the work done by knee extension and the peak power output at that joint. These results suggest that the individual joints may be modulated differently when whole-animal performance increases.