Tuning biomechanical energetics with an exoskeleton to improve stability during walking

Exoskeletons are promising tools to improve multiple aspects of our daily lives – they can increase our strength, improve our efficiency during walking and running, and lower our risk of injury during tasks such as lifting. Further, passive exoskeletons with elastic elements can be lighter and cheaper than their motor-driven counterparts, while also being able to assist us by modulating the mechanics of muscles and biological joints. However, one critical aspect of locomotion which we do not understand the influence of passive exoskeletons on is stability. This dissertation addresses the interaction between the areas of locomotion stability, muscle mechanics, and passive exoskeleton assistance through the lens of mechanical energetics. The overarching goal was to understand whether a passive hip exoskeleton can shift the mechanical energy demands imposed by a perturbation during walking by altering underlying muscle and joint dynamics to improve stability. Chapter 2 describes and validates a novel method for delivering transient, unilateral perturbations in belt speed on an instrumented treadmill. Chapter 3 assesses the effects of different perturbation timings on the mechanical energetics of the leg and joints, with a principal finding being the ankle of the perturbed leg and the knee of the unperturbed leg reflect the energetic demand of a perturbation. Chapter 4 extends this analysis to the level of a hip flexor/knee extensor muscle, the rectus femoris. Using a custom semiautomated application for tracking rectus femoris dynamics, the mechanical energetics at the level of fascicles and the muscle-tendon unit were estimated, with the principal finding that the rectus femoris better reflected the energetic demands of the hip than the knee on the contralateral leg. Finally, Chapter 5 assesses the influence of a passive hip exoskeleton on stability during perturbed walking both from the perspective of whole-body angular momentum and mechanical energetics. The principal findings from that chapter indicate a disconnect between definitions of stability effects, with the exoskeleton having deleterious effects on the fluctuation of momentum but limited effects on energetics. In all this dissertation contributes valuable first insights into proximal muscle mechanics during human walking and the potential impacts of passive exoskeletons on stability.

Date

2022-07-26

Resource Type

Text

Resource Subtype

Dissertation

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