Effects of a Powered Ankle Exoskeleton on Walking Biomechanics and Perception in Middle-Aged and Young Adults

Abstract

Walking is one of the activities of daily life with the highest energy expenditure. Ankle exoskeletons have been developed to assist with walking by rehabilitating function, enhancing user capabilities, and/or reducing physiological demands. However, ankle exoskeleton research has been conducted primarily with young adults. It is important to include individuals across the lifespan in research because aging affects gait mechanics. One age-related change is the distal-to-proximal shift, a phenomenon in which propulsive joint work shifts proximally from the ankle to the hip with increasing age. To ensure individuals of all ages can effectively use an ankle exoskeleton, the device must be tailored to the individual user. Powered exoskeletons use controllers that store and execute commands to determine how assistance is provided through control parameters (e.g., peak torque, quasi-stiffness coefficient). Tailored control parameters have been shown to reduce metabolic cost more than standard settings. Understanding how users perceive exoskeleton assistance is important, as perception is closely related to factors that influence performance and trust in the exoskeleton system. For example, age affects the ability to perceive forces, likely due to age-related changes in sensation and neuromuscular control. This dissertation examines powered ankle exoskeleton assistance during walking in both young and middle-aged adults. The first study evaluates gait characteristics and muscle activation resulting from modifications to the quasi-stiffness control parameter in young adults. The second study investigates gait characteristics, muscle activation, and energy expenditure while walking with and without an ankle exoskeleton in middle-aged adults, a population that has been underrepresented in ankle exoskeleton research involving able-bodied individuals. The third study evaluates the perception of changes in peak torque while walking with an ankle exoskeleton in both young adults and middle-aged adults. This dissertation contributes to the growing body of literature on ankle exoskeletons by providing insight into how middle-aged adults respond to powered ankle exoskeleton assistance and how changes in control parameters influence physiological outcomes and perception. These findings highlight the importance of considering individual differences when designing exoskeleton controllers to optimize performance and inform the development of future exoskeleton control strategies and training protocols, particularly for middle-aged adults.