PT  - JOURNAL ARTICLE
AU  - Gwendolyn M. Bryan
AU  - Patrick W. Franks
AU  - Seungmoon Song
AU  - Alexandra S. Voloshina
AU  - Ricardo Reyes
AU  - Meghan P. O’Donovan
AU  - Karen N. Gregorczyk
AU  - Steven H. Collins
TI  - Optimized hip-knee-ankle exoskeleton assistance at a range of walking speeds
AID  - 10.1101/2021.03.26.437212
DP  - 2021 Jan 01
TA  - bioRxiv
PG  - 2021.03.26.437212
4099  - http://biorxiv.org/content/early/2021/03/28/2021.03.26.437212.short
4100  - http://biorxiv.org/content/early/2021/03/28/2021.03.26.437212.full
AB  - Background Effective autonomous exoskeletons will need to be useful at a variety of walking speeds, but we do not know how optimal exoskeleton assistance should change with speed. Optimal exoskeleton assistance may increase with speed similar to biological torque changes or a well-tuned assistance profile may be effective at a variety of speeds.Methods We optimized hip-knee-ankle exoskeleton assistance to reduce metabolic cost for three participants walking at 1.0 m/s, 1.25 m/s and 1.5 m/s. We measured metabolic cost, muscle activity, exoskeleton assistance and kinematics. We performed two tailed paired t-tests to determine significance.Results Exoskeleton assistance reduced the metabolic cost of walking compared to wearing the exoskeleton with no torque applied by 26%, 47% and 50% at 1.0, 1.25 and 1.5 m/s, respectively. For all three participants, optimized exoskeleton ankle torque was the smallest for slow walking, while hip and knee torque changed slightly with speed in ways that varied across participants. Total applied positive power increased with speed for all three participants, largely due to increased joint velocities, which consistently increased with speed.Conclusions Exoskeleton assistance is effective at a range of speeds and is most effective at medium and fast walking speeds. Exoskeleton assistance was less effective for slow walking, which may explain the limited success in reducing metabolic cost for patient populations through exoskeleton assistance. Exoskeleton designers may have more success when targeting activities and groups with faster walking speeds. Speed-related changes in optimized exoskeleton assistance varied by participant, indicating either the benefit of participant-specific tuning or that a wide variety of torque profiles are similarly effective.Competing Interest StatementThe authors have declared no competing interest.EMGelectromyographyRMSroot mean square