Impact of a Portable Autonomous Exoskeleton on Human Exertional Metrics During Sloped Walking

Abstract

The Biomechatronics group of the MIT Media Lab has developed an autonomous powered exoskeleton capable of providing a significant metabolic benefit to the user when walking on level ground. To gain a better sense of the practicality and versatility of this system, an assessment of metabolic and biomechanical performance on surfaces other than level ground is warranted. While other groups have evaluated aspects of exoskeleton performance on inclined terrain, no group has provided a direct quantitative comparison of sloped walking without any device to sloped walking wearing a powered autonomous ankle exoskeleton. We hypothesized that a leg exoskeleton capable of providing a significant metabolic benefit on level ground through substantial positive mechanical power and minimal added distal mass would continue to provide a significant metabolic benefit on an incline, and that such a system would also provide no significant metabolic cost on a decline. In this study, the effect of the MIT exoskeleton on human exertional metrics was evaluated through measurement of respiratory metabolics while walking on an instrumented treadmill at +/- 15% grade. At the same time, electromyography was performed to evaluate differences in muscle activation. In four healthy male subjects, the exoskeleton was found to impart no net metabolic benefit nor net cost to the user during inclined walking or declined walking, with a trend suggestive of metabolic benefit on an incline and a trend toward added metabolic cost on a decline. The lack of significance is likely the result of the low sample size, however these trends are likely attributable to the much higher overall metabolic cost of inclined walking relative to the amount of mechanical power applied by the exoskeleton, and a net destabilizing effect of powered plantarflexion during careful ramp descent. In demonstrating lack of cost on an incline and highlighting a possible added metabolic cost during powered decline walking, this study further characterizes both the the practical utility as well the limitations of an autonomous powered exoskeleton for military, recreational, rehabilitative, or other use.