Meeting Abstract
Behaviors like chameleon tongue projection, a mantis shrimp punch, or a leaping frog are impressive examples of animal movements. These movements far exceed the mechanical power capacity of skeletal muscle. In order to amplify mechanical power, muscles stretch elastic structures prior to movement. This stores potential (elastic) energy. When elastic structures recoil, the stored energy is rapidly released to amplify power. Evidence for this catapult-like mechanism has been observed in even sub maximal frog jumps and in many species the mechanical power of a jump is well beyond the capacity of hindlimb muscles. If frog jumps are powered through the elastic recoil of tendons and the contraction of muscles is decoupled from the movement of the animal, then we would expect jumping performance to be largely independent of temperature. Yet, frog jump distance improves significantly with increased temperature. This apparent disparity suggests that either the contribution of elastic mechanisms is somewhat limited or that the mechanical properties of tendons have some degree of thermal sensitivity. We hypothesize that the maximum rate of recoil and energy release increase with temperature. To test this prediction we isolated the tendon tissue from bullfrog plantaris muscle-tendon unit. We then applied a 3% stretch to the tendon before rapidly unloading the tendon to measure the speed of recoil and rate of energy release. Experiments conducted at 10, 20, and 30°C show that tendon recoil speed increased significantly (p<0.05) with temperature. Thus, these findings suggest that rate properties of tendons do vary with temperature. Therefore, power-amplified behaviors using elastic mechanisms may not be completely insensitive to variation in environmental temperature.
