Meeting Abstract
42.4 Saturday, Jan. 5 Do hindlimb joints serve multiple functions during jumping in the Cuban tree frog? HSIEH, S.T.*; ROBERTS, T.J.; Harvard University; Brown University sthsieh@post.harvard.edu
Cuban tree frogs (Osteopilus septentrionalis) are some of nature�s best vertebrate jumpers, capable of exceeding 20 body lengths in one leap. Although these jumps are by necessity characterized as a single bout of explosive energy release, frogs are also able to maneuver during the push-off phase, such that the final center of mass trajectory is at an angle to the initial body orientation. We tested the hypothesis that the hindlimb joints in frogs serve different functions during a jump. Based on limb muscle morphology, we expected that distal joints would produce the greatest amount of power for the jumps, whereas proximal joints would exert a greater effect on controlling jump performance. Frogs were filmed using two synchronized, high-speed cameras filming at 500 fps while simultaneously recording three-dimensional ground reaction force (GRF) data with a custom-built tri-axial force platform. Hindlimb joint moments and power were calculated using three-dimensional inverse dynamics. During a jump, hindlimb joint extension proceeded proximal to distal. The speed of joint extension was least at the hip and greatest at the ankle. Ankle joint power remained constant and low during most of push-off and spiked shortly after peak vertical GRF, indicating the likelihood of elastic energy storage early in the jump followed by elastic energy release. Most of the power was produced at the ankle (64-83% of total power peak), and significantly less was produced at the hip and knee. Whereas this pattern was consistent for the ankle, joint power production at the knee and hip was much more variable. These data suggest differential function of hindlimb joints during jumping in frogs: while the ankle is responsible for the storage and amplification of power required for producing the long-distance jumps, the knee and hip may serve an added function of modulating jump performance. Supported by NSF grant 642428 to T.J.R.
