Meeting Abstract

69.11  Jan. 7  modeling time-varying fluid forces on an anuran foot to determine the power requirements of the ankle joint during swimming RICHARDS, Christopher T*; BIEWENER, Andrew A; Harvard University richards@fas.harvard.edu

During swimming, the anuran foot generates drag-based hydrodynamic power both by moving parallel to the direction of swimming (translation) and by pivoting about the ankle joint (rotation). Although translation and rotation are continuous throughout the propulsive stroke, these two components of foot motion are likely to be driven by two distinct groups of muscles. Proximal muscles extend the hip and knee joints to translate the foot whereas ankle extensors rotate the foot. Because drag-based hydrodynamic power is proportional to the square of the total velocity of the foot (the sum of translational and rotational velocity), ankle muscles must produce power to rotate the ankle joint in addition to generating instantaneous force to resist drag as proximal muscles translate the foot. We hypothesize, therefore, that the role of the ankle is twofold: (1) to produce hydrodynamic power by rotating the foot rapidly and (2) to produce large forces rapidly to control the orientation of the foot as it translates. Preliminary model results suggest that proximal joints (hip and knee) generate roughly 84% of the drag power through translation alone. These findings suggest that the principal role of the ankle joint in anuran swimming is not to generate hydrodynamic power, but to transmit power from proximal joints by rotating the foot, such that it is oriented perpendicular to the flow during rapid translation.