Meeting Abstract

69.5  Monday, Jan. 6 09:00  The mechanics of elastic loading and recoil in anuran jumping ASTLEY, H. C.*; ROBERTS, T. J.; Georgia Institute of Technology; Brown University henry.astley@gmail.com

Many animals use catapult mechanisms to produce extremely rapid movements for escape or prey capture, resulting in power outputs far beyond the limits of muscle. In these catapults, muscle contraction loads elastic structures, which then recoil to release the stored energy extremely rapidly. Many arthropods employ exoskeletal latches to lock the joint in place during the loading period, which can then be released to allow joint motion via elastic recoil. However, jumping vertebrates lack a clear anatomical catch, yet face the same requirement to load the elastic structure prior to movement. There are several potential mechanisms to allow loading of vertebrate elastic structures, including the gravitational load of the body, a variable mechanical advantage at the ankle, and forces generated by the extension of proximal joints. To test these hypothesized mechanisms, we collected simultaneous 3D kinematics via XROMM and single-foot forces during the jumps of three Rana pipiens. We calculated joint mechanical advantage, moment, and power using inverse dynamics at the ankle, knee, hip and ilio-sacral joints. We found that the hip moment exerts a downward force at the knee which counteracts the moment of the ankle, and the reduction in this downwards force allows the ankle to extend using elastic recoil. Mechanical advantage also changes throughout the jump, with the muscle contracting against a poor mechanical advantage early in the jump during loading and a higher mechanical advantage late in the jump during recoil. These mechanisms both serve to oppose joint motion during elastic loading then allow it during elastic recoil, facilitating increased elastic energy storage and improved jump performance.