Meeting Abstract

18.3  Thursday, Jan. 3  Modeling the kinematic determinants of anuran swimming performance RICHARDS, Christopher T.*; BIEWENER, Andrew A.; Harvard University; Harvard University richards@fas.harvard.edu

Swimming anurans generate hydrodynamic thrust by extending their leg joints to produce translational and rotational foot motion. Variation in recruitment of extensor muscles at different joints can greatly alter foot kinematics, potentially allowing frogs to modulate thrust during a stroke by controlling the strength and timing of translation versus rotation. We aim to explore the hypothetical range of kinematic variation to understand how joint coordination influences swimming velocity, acceleration and glide distance. Our model consists of an ellipsoid body with two feet driven by actuators at the hip, knee (causing foot translation) and ankle (causing rotation). We input joint kinematics (limited by Xenopus laevis joint ranges of motion) into a blade element model and simulated swimming velocity profiles using two coupled differential equations estimating 1) hydrodynamic forces from a thin plate foot and 2) the acceleration of the frog body. As expected, the model predicted maximal swimming velocity, acceleration and glide performance when all joints extended fully (rapid translation and rotation). At minimum ankle rotation (pure translation), velocity and acceleration were reduced only by 20%. However, glide performance (defined as the swimming speed at the end of the power stroke) was reduced by 60% in the absence of rotation, suggesting that proximal joints effectively accelerate a frog by translating the foot, whereas rotation allows longer glides by sustaining thrust through the stroke. These preliminary results suggest that frogs may employ different limb kinematics to suit the various locomotor tasks in swimming.