Exoskeleton Footwear to Improve Walking Performance and Subject-reported Preference

Claudication due to peripheral artery disease (PAD) causes patients to walk less and slower, lose independence in daily living activities, and be sedentary compared to their healthy counterparts. The investigators' research has identified functional limitations in the walking patterns of claudicating patients. The most prominent and consistent deficit is of the posterior calf muscles, the ankle plantarflexors, to generate healthy ankle torque and power during walking. Previous work in the investigators' laboratory has established that these functional deficits are related to the presence of a myopathy in the legs of patients with PAD which is characterized by myofiber degeneration and muscle fibrosis. An intervention that compensates for impaired muscle physiology and performance is needed to improve walking ability and independence in patients with PAD.

The long-term goal of this project is to improve the quality of life of patients with PAD by using assistive exoskeletons. Currently, there is a critical treatment gap for those patients with PAD whose disease presentation does not warrant operative revascularization (based on risk-benefit analysis that considers multiple factors including disease severity, comorbid conditions and operative risk), but who desire to regain their walking ability and independence. Ankle-foot orthoses have recently been implemented to reduce the demands for biological ankle plantarflexor torque and to compensate for power deficiency. Biological ankle torque/power is torque/power generated by the plantarflexor muscles apart from that provided by an assistive device. The investigators have developed a lightweight and low-cost 3D printable elastic exoskeleton and footwear combination called exoskeleton footwear (EF). The EF assists with push-off by using springs that mimic ankle plantarflexor forces. Exoskeletons that assist propulsion address both the myopathy and low blood flow problems associated with claudication. Mechanical force from the EF compensates for insufficient muscle propulsion force, while decreasing blood flow demand and the muscular stress caused by ischemia. A properly designed exoskeleton will likely allow patients with PAD to walk longer without pain or walk the distance needed for completing daily activities with less stress to the affected leg. As a first step the investigators propose to determine the effect of EF on walking performance, focusing on how different levels of EF support contribute to changes in the biological ankle torque and power, energy cost, and calf muscle oxygenation. The investigators will test healthy older adults to ensure and confirm comfort, low risk of injury to the foot and calf, and high potential for device adoption in patients with PAD.

The EF will then be evaluated in patients with PAD. Healthy older individuals are selected for the initial phase of the project because, like patients with PAD, they produce less push-off torque and power during walking compared with healthy young; making them an appropriate model for PAD limitations. Furthermore, compared to patients with PAD, healthy older can tolerate longer walking trials, which are necessary to identify effective device parameters and also have a significantly lower risk of developing foot and calf injuries while the comfort and shape of the EF are assessed and adjusted to accommodate individuals with different foot and leg morphologies.

Hypothesis: Walking performance will improve with EF in healthy older and patients with PAD. The investigators hypothesize there will be an EF assistance level to satisfy subject-reported preference and walking performance goals.

Specific Aim 1: To determine the levels of EF assistance force which produce better walking performance in older subjects. Improvements in walking performance will be assessed by measuring how different levels of EF assistance contribute to changes in the biological ankle torque and power during push-off, the energy cost of walking, and the calf muscle oxygenation during walking.