Abstract
Over 6 million people in the United States use assistive devices to improve their walking performance [Kaye et al., 2000]. In the case of people with musculoskeletal gait impairments this means finding the best methods to reduce falling and mitigate lack of stamina [Gross et al., 2018]. One common assistive device is a passive posterior walker [Durkin et al., 2016], where the user stands within the walker’s frame and, while holding the handles of the walker at their sides, pulls the walker along behind them as they walk forward. Walking with a posterior walker provides a mechanical advantage and sensory feedback that improves balance control, or stability, of the user [Bateni and Maki, 2005]. While improving stability is necessary in many populations with walking impairments, it only solves part of the walking performance problem. Improved stability will encourage people to walk more, but if the price of this improved stability is that they become exhausted sooner, they will not actually be able go any farther.
The end goal of this work was to develop a simulation tool capable of assessing how different methods of applying propulsive force might aid the user of an assistive device. To get there, we began by developing and analyzing function-based performance metrics for gait, including a stability metric able to describe differences in populations of non-fallers and an energetics metric able to quantify the cost of walking from a mechanical, as opposed to a physiological, basis. We then used these metrics to quantify how walking with a posterior walker affects their user’s stability and cost of walking. With this understanding established, we then developed a predictive simulation framework to test methods of powering a posterior walker to add propulsive forces to the user, with the intention of reducing the effort required to walk with the walker. Finally, the predictive simulation framework was validated by testing a subset of propulsion methods in the lab using a powered posterior walker, co-developed with Barron Associates Inc.
Ultimately, this work resulted in a useful predictive simulation framework to assess how possible propulsive forces may alter walking performance. This tool will dramatically increase the assistance methods that can be investigated to improve the aid assistive devices provide to their users. Potential improvements can quickly be simulated in silico, and pitfalls can be found before taking these controls into a laboratory setting. This will make laboratory testing of devices safer and more streamlined. In the use case presented here, this framework is being used to develop a posterior walker with motorized rear wheels to reduce the effort required for walking without losing the device’s stability benefits. Providing a posterior walker that reduces the workload of walking will keep this population walking longer, providing critical exercise and continued muscle development. Developing a way to better improve assistive devices will help the individuals reliant on their aid stay active longer, improving their quality of life and providing key physiological, mental, and social benefits.
