Meeting Abstract

98.10  Wednesday, Jan. 7  Muscle performance during frog jumping: influence of series elasticity on muscle length-tension behavior AZIZI, E*; ROBERTS, TJ; Brown University; Brown University manny_azizi@brown.edu

The remarkable jumping ability of most frogs cant be explained solely from muscle properties. The maximum power available from hindlimb muscles has been shown to be insufficient to power these ballistic movements. Its been suggested that frogs utilize elastic energy storage in tendons to amplify muscle power during jumps. We explore this elastic mechanism by quantifying the activation timing and length changes of the bullfrog plantaris muscle during jumps. We hypothesize that the muscle will be active and begin to shorten prior to ankle extension, functioning to store elastic energy in tendons. This initial fiber shortening can be substantial and may limit the force generating capacity of fibers due to muscle’s length-tension effects. Therefore, we also characterize the length-tension properties of the same muscle using the same transducers immediately following jumping experiments. This protocol allows us to map the in vivo muscle length changes onto the length-tension curve in order to test the hypothesis that significant muscle shortening against tendons decreases force output. We find support for the use of elastic energy storage by showing that the plantaris fibers become active and begin shortening in advance of ankle extension. We also find that the plantaris fibers do not develop passive force until stretched to relatively long lengths. This allows the resting length of the muscle to be shifted towards the descending limb of the active length-tension curve allowing most of the fiber shortening during a jump to occur over the plateau of the length-tension curve. The passive compliance of this muscle enhances active force production during an elastic energy storage mechanism reliant on muscle shortening. Supported by NSF grant 642428 to TJR.