Organismal physics: Resonance mechanics, self-excited oscillations and the multiscale physics of muscle underlying agile flight of insects

Via Zoom

The ability to move is a trait of all animals. Yet how do animals, including ourselves, get around in this complex and uncertain world with an ease and agility we find hard to recreate in engineered systems?

Underlying these behaviors are compositions of immensely complex physiological subsystems (brains, muscles, bodies), yet what often emerges through evolutionary timescales and environmental interactions is a functional performance that can (sometimes) afford simple analysis on the scale of behavior. In this talk, I will use the agile locomotion of insects to show how an organismal physics approach can give insights into this emergent, functional simplicity. I will show how insects operate as resonant mechanical systems to power flight but do not necessarily operate at their resonant frequency because of consequences for control. We will explore how insects have evolved two different strategies for powering this resonant flight system using muscles that either provide periodic oscillatory forcing or use a stretch-responsive property to set up self-excited limit cycles. While these two strategies have been known for some time, we find that they can be unified in a single dynamic systems framework that shows how major evolutionary transitions reflect transition in this dynamical response. Finally, I will discuss how muscle’s ability to power movement is shaped by its unusual multiscale structure. High-speed x-ray diffraction through living muscles shows that living muscle is active crystalline matter – the regular arrangement of actin and myosin filaments produces a lattice that dynamically changes spacing as a muscle contracts. A single nanometer difference in muscle lattice spacing can account for how one muscle acts like a motor while another acts like a brake. We cannot yet emulate the motility seen in nature, nor derive behavior, but the emergent dynamics of animal locomotion is an exciting opportunity to explore how complexity gives way to function and the physical and physiological mechanisms that are the enablers of this performance.

Host: Zachary Jackson and Bingkan Xue