Frog jumping as a model for muscle performance
Frog jumping provides an excellent model for investigating the limits to muscle-powered movement. A jumping frog has only a very brief period of time, and a single muscle contraction, to develop the substantial mechanical power necessary to launch on a successful jump trajectory. There is good evidence that frogs escape the limits of muscle power by using an elastic mechanism, whereby muscle work is stored slowly in tendons and released rapidly to power the jump. We are working to understand how this mechanism works, with the goal of revealing fundamental rules that govern how muscles and tendons function together. Areas of focus include the role of the skeletal lever system and passive muscle elasticity, as well as comparative studies to examine the link between muscle properties and locomotor performance.
Performance of muscle-tendon systems for energy absorption
We most commonly think of muscles as motors for producing mechanical power, such as in a frog jump. But muscles also absorb mechanical energy. In terrestrial systems, energy absorption is no less important than energy production, as it is essential for deceleration, running, jump landing, and maneuvering. Yet, we know relatively little about the control, energetics, or mechanics of energy absorption by muscles during natural movements. Our current studies in this area include an examination of the role of tendons in energy absorption. We use wild turkeys as a model, because we can measured force, length and activity in individual muscles in these animals. A central hypothesis is that tendons act as a buffer, storing energy rapidly and releasing it slowly to muscles during activities like jump landing and downhill running. Energy-absorbing activities are often associated with damage to muscle and other structures, thus they are important both to our understanding of human musculoskeletal health, and to our understanding of how the risk of injury has shaped muscle, tendon and bone properties through evolution.
Determinants of muscle force and velocity
Muscles change shape when they contract. Recently we showed that these shape changes vary depending on the force of contraction, and that variable shape changes influence the force and velocity output of the muscle. This example illustrates a question of ongoing interest: how are the force and speed of muscle contraction influenced by muscle architecture, the connective tissue structures that envelop muscles, and the dynamic changes in these structures that occur during a contraction? We are using both isolated muscle and in vivo approaches to understand how tissue and organ-level function influence the mechanical performance of muscles.
Energetics and mechanics of muscle function in walking and running
We have an ongoing interest in how the elastic function of tendons influences the mechanics of force production in muscles during walking and running. This research seeks to advance our understanding of the determinants of the metabolic energy cost of locomotion. A central hypothesis of this work is that the elastic function of tendons allows muscle contractile elements to operate at lengths, velocities, and power outputs that favor economic force production. This work involves both experiments with isolated muscle-tendon units and studies of muscle mechanical function during locomotion.