Altering Compliance of a Load Carriage Structure in the Medial-Lateral Direction
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For work or recreation, many individuals transport heavy loads within a backpack. Carrying substantial weight while walking typically causes an increase in muscle activity, metabolic energy expenditure, and increases likelihood of injury. Understanding different modes in which a carried load can interact with a user could help inform design decisions of smart load carriage devices that minimize the burden of carrying weight. We explore this concept in this thesis by investigating a novel mode of load carriage: allowing carried weight within a backpack to oscillate in the medial-lateral direction. To date, our understanding of oscillating load carriage dynamics are constrained to the sagittal plane. Previous studies have explored vertically oscillating carried weight and have observed reductions in peak load carriage forces experienced by the user and reductions of the metabolic cost of walking. We seek to expand this understanding by investigating medial-lateral oscillating load carriage and its effects on gait. We created a novel load carriage device, and through device modelling, chose device parameters that resulted in out-of-phase mass oscillations with respect to trunk medial-lateral excursions. We found that peak load carriage forces were significantly reduced when walking with an oscillating mass, compared to a fixed mass. However, contrary to peak load carriage forces, the metabolic power of walking significantly increased. We identified an increase in the frontal plane interaction moment experienced by the user during oscillating conditions that increased with mass oscillation amplitude. This suggested that perhaps reducing the amplitude of mass oscillations may improve the metabolic response of users. The second objective of this thesis was to generate electricity from the oscillations of the carried mass. We developed an energy harvesting module that generated 0.22 W of electricity while carrying 9 kg of weight. The energy harvesting module also acted as a system damper reducing the amplitude of mass oscillations. We found that with reduced mass oscillations, the metabolic power required to walk with the device was not significantly different than walking with the mass rigidly fixed. The knowledge garnered through this exploration of medial-lateral load carriage will help inform future decisions on smart load carriage device design.