Meeting Abstract

66.6  Thursday, Jan. 6  Using bio-robotic tools to explore muscle force-length and force-velocity properties in aquatic locomotion RICHARDS, Christopher T.*; CLEMENTE, Christofer J.; Harvard University richards@fas.harvard.edu

Understanding swimming biomechanics is challenging because of the complexities of fluids and the poor knowledge of neural input versus muscle output. Recent bio-robotics advances explore how various limb motions and morphologies influence fluid propulsion. Separately, physiologists have characterized muscle dynamics in isolation from the external environment. Yet, muscle mechanical output comes not only from neural activation and intrinsic muscle properties, but also from coupled interactions with fluid forces. Using a servo motor-driven robotic frog foot, we tested how interactions between neural activation, intrinsic muscle properties and limb morphology determine contractile dynamics. To initiate motion, an activation waveform was sent to a Hill-type muscle model in a computer. Every 0.1 ms, motor force output was updated from motor position and velocity feedback, causing the servo motor to behave like muscle. Foot motion output emerged from interactions between the water and the motor as dictated by force-length (FL) and force-velocity (FV) properties in the computer model. Using muscle FL and FV properties from frog muscle, we varied activation magnitude and resting length (RL). Preliminary data suggest that as activation increases, peak motor force and power increase ~2-fold from 0.36 to 0.65 N and from 2.1 to 5.6 mW, respectively. Yet, at each activation level, altering the virtual muscle’s RL (from 90 to 120% optimal length) enhanced motor power by more than 3-fold. Corroborating recent work in jumping frogs, our preliminary findings suggest that FL effects may be as important as activation in determining the development of muscle force against a hydrodynamic load.