Nervous systems are built to interface with the external world and control behavior. Behavior unfolds as a set of actions elicited by the integration of stimuli with internal states. Our field has made considerable progress toward understanding how sensory signals are converted into internal representations that direct motor commands. By contrast, comparatively little is known about how stereotyped actions —walking for instance— emerge from coordinated patterns of muscle contractions generating controlled and reproducible movements. In this KITP program, we will examine the physical principles governing locomotion, the ability to move in space in a purposeful way. Although the modalities of locomotion can dramatically differ in fluids (swimming and flying) and in terrestrial conditions (crawling and walking), all forms of motion rely on exerting forces on the environment to produce thrust while possibly sensing forces exerted by the environment on the body through proprioception.

Physics is central to the genesis and the control of locomotion. Connecting the output of the brain with movement is described in terms of mechanics. We will review the state of knowledge about the neuro-mechanics of locomotion and sensation with a focus on proprioception. We will compare the solutions that have evolved to permit motion in flying, swimming and walking animals. We will examine physical mechanisms that produce different modes of locomotion in the absence of inputs from the brain. We will then evaluate the role of brain inputs in the organization of stereotyped sequences of movement. We will explore how dynamical systems theory and computational modeling can be used to describe feedback loops that bind sensation and action. Finally, we will reach out to the field of robotics to define how working hypotheses about neuromechanics can be tested in the physical world as well as in real-world conditions.