SUMMARY

Wearable devices that alter foot-ankle mechanics, such as exoskeletons and modified footwear, can change locomotion performance. For example, ankle exos have been shown to reduce metabolic cost of walking, while high-heeled shoes have been shown to increase metabolic cost. Previous studies provide insights on how foot-ankle devices alter biomechanics and energetics, but the mechanism linking altered biomechanics and whole body metabolic cost remains unclear for human walking. Additionally, little is known about how small changes in loading on the biological system over long time periods impacts muscle-tendon (MT) structure. These potential changes in structure may lead to altered function. The goal of this thesis was to ask: 1) How do devices that change foot-ankle mechanics alter whole body metabolic cost? 2) Can relatively small changes in musculoskeletal loading over long time scales impact MT structure? and, 3) How do changes in MT structure impact locomotion function? We developed computational and experimental frameworks to investigate how acute and chronic changes to MT mechanics impact structure and energetic cost of walking. Through our work, we showed that A) active muscle volume at the ankle can drive whole body metabolic cost of walking (in-vivo), B) the number of steps taken in passive ankle exos (in-simulation) and modified shoes with raised heels or raised toes (in-vivo) drives calf MT material and morphological adaptation during long-term use of devices (i.e., over months) , and C) chronic changes in calf MT properties can profoundly impact locomotion performance (in-vivo). Taken together, our research pushes fundamental understanding of MT structure-function of the human foot-ankle during walking to ecologically relevant time scales. In doing so, our research can inform the field of wearable technology offering guiding principles for design, control and/or prescription based on emerging principles of long term neuromechanical adaption of end users.