Analyzing Modeled Torque Profiles to Understand Scale-Dependent Active Muscle Responses in the Hip Joint.

Fletcher R Young,Matthew C Tresch,Roger D Quinn,Hillel J Chiel,Alexander J Hunt,Charles J Heckman

doi:10.3390/biomimetics7010017

Fletcher R Young, Matthew C Tresch + Show 4 more

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https://doi.org/10.3390/biomimetics7010017

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Animal locomotion is influenced by a combination of constituent joint torques (e.g., due to limb inertia and passive viscoelasticity), which determine the necessary muscular response to move the limb. Across animal size-scales, the relative contributions of these constituent joint torques affect the muscular response in different ways. We used a multi-muscle biomechanical model to analyze how passive torque components change due to an animal’s size-scale during locomotion. By changing the size-scale of the model, we characterized emergent muscular responses at the hip as a result of the changing constituent torque profile. Specifically, we found that activation phases between extensor and flexor torques to be opposite between small and large sizes for the same kinematic motion. These results suggest general principles of how animal size affects neural control strategies. Our modeled torque profiles show a strong agreement with documented hindlimb torque during locomotion and can provide insights into the neural organization and muscle activation behavior of animals whose motion has not been extensively documented.

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Locomotion involves the coordination of many different neuromechanical systems
Multi-legged locomotion is a common task performed by animals that vary broadly in size, the fundamental components of the nervous system remain mostly consistent
We demonstrate how the size-scale of an animal affects the relative contributions of the constituent joint torques, resulting in the emergence of at least two different modes of control when the size-scale is relatively large or relatively small

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Introduction

Locomotion involves the coordination of many different neuromechanical systems. High-level descending commands and low-level reflex pathways work together to control animal limb segments. The constituent properties of an animal’s biomechanics require its nervous system to be tuned for the tasks that the animal routinely performs [1,2]. Multi-legged locomotion is a common task performed by animals that vary broadly in size, the fundamental components of the nervous system remain mostly consistent. A leg performs different functions during its swing and stance phases of movement and, requires different muscle activations [3]. Motion is assumed to be dominated by the passive properties of an animal’s limb and is affected by gravity, similar to a pendulum. In contrast, the leg provides power that propels the animal forward and involves a complex coordination of muscle activity to counteract the destabilizing effects of gravity (similar to an inverted pendulum) and maintain posture [6,7]

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