Energy optimization and locomotion control: task, strategy, and mechanisms

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Why does an individual walk or run as they do? Determining why specific control strategies are implemented is the goal of our research program. Based on emerging evidence, we suspect that minimizing energetic cost has an important effect on the movement strategy chosen. We use a range of manipulations to expose the role of energetic cost on individual response in order to map energetic cost effects and identify the mechanisms involved in minimizing locomotion cost. These studies are organized into three project streams that my group will work on over the next 5 years (and beyond). Normal walking and running are a solution to the challenges faced by moving on legs, but the actual problems solved by these gaits are not necessarily self-evident. It is our goal to identify the constraints and opportunities available. This fills a critical gap where sensory input and motor output coordination and within limb mechanics must integrate with the physical (dynamic) environment the individual or organism moves within. Our focus is on the latter component, determining what the leg needs to do in order to generate effective locomotion, and why a particular solution is appropriate over all others (and by how much so). This as a key factor putting central nervous system (CNS) action within a functional context, so the motor control decision process can be analyzed and interpreted. The long term goal is achieved by considering the solution space available to the CNS and evaluating how a normally functioning individual/organism selects from that array of options. Short term studies employ a three stage process: (a) use optimization models to identify the functional solution space available, (b) verify that the models represent realistic empirical (human or animal) movement in the same circumstance, then (c) interrogate the model to identify the trade-offs that determine the optimization solution. Each project stream opens a novel approach to the core problem (understanding gait strategy selection). The projects allow controlled manipulation of the gait environment, providing the opportunity to directly compare model predictions (hypothesis) with empirical quantification of motor strategy expression. Organization of projects into related streams allows division of projects that make the projects amenable to participation by HQP at both the undergraduate and graduate levels. Project stream 1 uses a custom designed computer controlled oscillating harness that applies a cyclic impulse to the trunk, enabling analysis of the machine-human interaction. Project stream 2 addresses the problem of quadrupedal gait, developing original dynamics based models to understand how animal form affects locomotion. Project stream 3 takes advantage of the unusual movement strategies employed in parkour (urban gymnastics) to quantitatively map energetic consequences of a number of standard maneuvers that will allow direct experimental evaluation of movement strategy choice.