My research focuses on the biomechanics of animal locomotion, at the intersection between biology and physics. In order to move through their environment, animals must use physiological processes to generate force, transmit this force via the musculoskeletal system and morphology, and control it via the nervous system, all while navigating through sometimes mechanically complex and heterogeneous environments. I use a variety of systems to study these principles, including snakes, frogs, and early tetrapods. Snakes are capable to traversing a tremendous range of environments with a greatly simplified body plan, dramatically changing their interactions with the environment using different control strategies and gaits, such as sidewinding, lateral undulations and concertina locomotion. Frogs use elastic tendons in a catapult mechanisms, allowing them to generate jump power outputs far beyond the limits of muscle power, showing the potential for musculo-skeletal morphology to dramatically alter function. And early tetrapods moved through a novel and challenging mechanical environment with primitive limbs and limited control, posing an intriguing biomechanical puzzle. I study these and other systems using a variety of techniques on the biological systems (e.g. motion capture, high-speed video, inverse dynamics, in vitro muscle testing), along with construction of biomimetic robots and robophysical models, which allow us to command different control schemes and experimentally manipulate morphology in a controlled, repeatable manner.
The transition from life in the water to life on land is one of the most significant evolutionary events since multicellularity evolve, and resulted in a wide range of mechanical and physical challenges for previous aquatic organisms to adapt to. A key challenge is that of locomotion, as these organisms were transitions from an environment in which their body weight was mostly supported via buoyancy and propulsion could be achieved by hydrodynamic interactions, into an environment in which the body must either be supported by limbs or dragged on the substrate and propulsion can only be generated by substrate interactions. My previous work has included the interaction between the organisms and the flowable, granular substrates such as sand and mud which predominate in shoreline habitats. These substrates can either jam like a solid of yield and flow like a fluid, resulting in complex interactions between the substrate and organism. My colleagues and I found that using a tail along with limbs may have provided a crucial benefit, allowing organisms to traverse a wider range of substrate conditions with greater reliability. Future work will include dynamics of underwater walking, how this behavior may have preceded and developed into terrestrial walking, and how it can be replicated in underwater vehicles for exploration.
Elongate, limbless body forms are widespread among animals, including numerous cases of secondary convergence on this form, with snakes being the most widespread and successful of these secondarily limbless groups. In spite of their lack of limbs, snakes can swim, climb, glide, slither through dense vegetation, crawl through tunnels, and sidewind across dunes, with many species being capable of most of these behaviors. We seek to understand the fundamental mechanics and control of these diverse modes of snake locomotion, particularly their interactions with the environment, and to replicate these feats with robotic systems to enable access into the cluttered, complex, confined environments in which snakes excell.
Frogs are one of the most capable jumpers among vertebrates, often achieving jump distances of dozens of body lengths, over 2 meters in the most exceptional species. The crucial feature of these jumps is a "catapult mechanism" in the frog leg, which allows the large calf muscle to slowly load energy into an elastic tendon, which then recoils and releases the stored energy much more rapidly than muscle would be capable of. Such catapult mechanisms require a catch, but unlike invertebrates (which typically have an anatomical latch to control loading and recoil), frogs rely on a dynamic catch mechanism. We seek to investigate the mechanics of this catch mechanism, its evolution, and the overall evolution and biomechanics of frog jumping in order to understand how to control and power high-acceleration movements in a controllable fashion.
Interested in joining the lab? We are always looking for enthusiastic students with an interest in animal locomotion, including both undergraduates and prospective graduate students. Email Dr. Astley for more information.