Step-to-Step Ankle Inversion/Eversion Torque Modulation Can Reduce Effort Associated with Balance
Myunghee Kim1, Steven H Collins1,2,3
1Experimental Biomechatronics Laboratory, Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, United States.
Frontiers in Neurorobotics
|November 30, 2017
Summary
Ankle torque modulation in prosthetic feet can significantly reduce the energy cost of walking for below-knee amputees. This control strategy improves balance and reduces metabolic effort, paving the way for more efficient prosthetics.
Area of Science:
- Biomechanics
- Robotics
- Rehabilitation Engineering
Background:
- Below-knee amputation increases walking energy expenditure, largely due to impaired balance.
- Previous research demonstrated that controlling push-off work can reduce balance-related effort.
- Simulations suggested that modulating ankle inversion/eversion torque could further enhance balance.
Purpose of the Study:
- To investigate the impact of ankle inversion/eversion torque modulation on balance-related effort in below-knee amputees.
- To assess the metabolic cost reduction achievable with active control strategies in prosthetic ankles.
Main Methods:
- Employed a multi-actuated ankle-foot prosthesis emulator in five below-knee amputee participants.
- Implemented stabilizing and destabilizing ankle torque controllers, counteracting or amplifying center-of-mass deviations.
- Maintained constant average ankle torque and prosthesis work across conditions to isolate balance-related effects.
Main Results:
- High-gain stabilizing ankle torque control reduced metabolic cost by 13% compared to a zero-gain controller (p=0.05).
- Four out of five participants showed reduced metabolic rates with subject-specific stabilizing controllers, averaging a 9% reduction (p=0.05).
- No significant changes in average prosthesis mechanics were observed, indicating improvements stemmed from dynamic balance control.
Conclusions:
- Step-to-step modulation of ankle inversion/eversion torque effectively reduces metabolic cost during walking for amputees.
- This active control strategy shows promise for enhancing balance and reducing walking effort in future active ankle-foot prostheses.
- Dynamic torque modulation represents a viable approach to improve energy economy and gait stability in individuals with lower-limb loss.
