Effects of Ankle Exoskeleton Power and Actuation Timing on Movement Variability and Metabolic Cost of Walking
Advisor Information
Philippe Malcolm
Location
Dr. C.C. and Mabel L. Criss Library
Presentation Type
Poster
Start Date
3-3-2017 2:15 PM
End Date
3-3-2017 3:30 PM
Abstract
Walking is one of the most primal movements and an essential part of everyday life. While humans use many strategies to reduce metabolic energy cost, walking still requires a considerable amount of metabolic energy. Lower extremity exoskeletons have become an established technology designed to reduce metabolic cost. Recently, it was reported that they might increase the variability of the locomotor system making the system more noisy and unstable, but optimal assistance properties for gait variability remain unclear. This could be a main concern for people with a mobility disorder. We investigated the effect of ankle exoskeleton power and actuation timing on gait variability and metabolic energy cost of walking. Data was collected for ten healthy participants wearing a powered ankle-foot exoskeleton during a 4-minute treadmill walking trial at 1.25 m∙s-1 in ten different assistance conditions. Largest Lyapunov exponent (LyE) was calculated to quantify the pattern of stride-to-stride fluctuations of the ankle angle kinematics. The metabolic rate and LyE were compared between conditions. Optimal assistance was achieved at 42% of the stride and average power of 0.4 W∙kg-1 for both the LyE and metabolic rate. This resulted to a 50% lower LyE and a 21% reduction in metabolic cost compared to walking with the exoskeleton deactivated. These results emphasize the importance of optimizing exoskeleton actuation properties to provide a more stable and metabolic efficient human locomotor system.
Effects of Ankle Exoskeleton Power and Actuation Timing on Movement Variability and Metabolic Cost of Walking
Dr. C.C. and Mabel L. Criss Library
Walking is one of the most primal movements and an essential part of everyday life. While humans use many strategies to reduce metabolic energy cost, walking still requires a considerable amount of metabolic energy. Lower extremity exoskeletons have become an established technology designed to reduce metabolic cost. Recently, it was reported that they might increase the variability of the locomotor system making the system more noisy and unstable, but optimal assistance properties for gait variability remain unclear. This could be a main concern for people with a mobility disorder. We investigated the effect of ankle exoskeleton power and actuation timing on gait variability and metabolic energy cost of walking. Data was collected for ten healthy participants wearing a powered ankle-foot exoskeleton during a 4-minute treadmill walking trial at 1.25 m∙s-1 in ten different assistance conditions. Largest Lyapunov exponent (LyE) was calculated to quantify the pattern of stride-to-stride fluctuations of the ankle angle kinematics. The metabolic rate and LyE were compared between conditions. Optimal assistance was achieved at 42% of the stride and average power of 0.4 W∙kg-1 for both the LyE and metabolic rate. This resulted to a 50% lower LyE and a 21% reduction in metabolic cost compared to walking with the exoskeleton deactivated. These results emphasize the importance of optimizing exoskeleton actuation properties to provide a more stable and metabolic efficient human locomotor system.