Understanding adaptive mechanisms in locomotion by integrating motor control, tissue performance and mechanical constraint

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Animal locomotion is the result of a complex combination of neural commands, tissue performance and environmental mechanical constraint. Our understanding of how these combine to result in flexible animal locomotion is limited, as demonstrated by the inability of engineered robots to navigate complex environments. My research program aims to build on what we know about active tissues (nerves and muscles) and apply it in the context of the system's passive constraints (material properties of bones, connective tissue and the external environment). We will use the different mechanical environments associated with water and land to test changes in behaviour and tissue performance during locomotion. From tissues to the whole-animal, this research program uses comparative biomechanics, bio-material properties testing and modeling to clarify the mechanisms that drive locomotory performance. Objective 1: Quantify mechanical constraint in locomotion. We will quantify motor control patterns (electromyography techniques) and reaction forces (force-plate and particle imaging velocimetry techniques) during free walking and swimming in a model amphibious fish. Extracted data will guide material properties testing of both active (muscle) and passive (bone and connective) tissues to test the hypothesis that a changing external force environment influences the safety factor within which animal tissues operate. Quantification of the structural contribution of passive tissues and changing muscle performance through novel ranges of motion will address predictions on how external and internal forces constrain biomechanical performance and, over the longer term, cause plastic tissue responses. Objective 2: Predicting performance through modeling. Experimental data from whole animal and tissue experiments will inform Hill-type and finite element models to map force profiles experienced by fins and body throughout a step/swim cycle. These models will test the hypothesis that bone and muscle morphological plasticity is induced by a change in environmental forces by quantifying the magnitude and orientation of forces that cause tissue plasticity. Objective 3: Quantify the effect of plasticity on performance. Developmental plasticity can dramatically change an animal's form; how this change impacts performance is underexplored. Using our established techniques for raising fish on land, we will link plasticity to functional performance by analyzing changes in behaviour and tissue material properties in land acclimated individuals. Acclimated fish data will test individual tissue/force models (Obj. 2) with a goal to produce an overarching predictive model that includes the effects of plasticity on tissue performance and overall animal function. This research program iteratively uses a diversity of approaches to integrate active tissue behaviour with passive mechanical constraints to explain the adaptive capacity of animal tissues and resulting locomotory performance.