Improving reaching with functional electrical stimulation by incorporating stiffness modulation.

Area of Science:

• Neuroscience
• Biomedical Engineering
• Rehabilitation Robotics

Background:

• Functional electrical stimulation (FES) combined with intracortical recordings shows promise for restoring upper-limb function after spinal cord injury.
• A challenge in FES is that multiple muscle stimulation patterns can achieve a desired limb position, impacting performance and energy efficiency.

Purpose of the Study:

• To investigate the impact of modulating antagonist muscle coactivation during FES on reaching performance and energy consumption.
• To develop and optimize a method for automatically adjusting coactivation levels based on decoded kinematic information.

Main Methods:

• Utilized simulations to test a suite of lookup tables with varying coactivation levels for arm reaching control.
• Optimized a function to automatically switch between coactivation tables based on decoded endpoint speed and its derivative.
• Compared performance and energy usage of the dynamic modulation method against fixed coactivation levels.

Main Results:

• Dynamically modulating limb stiffness through coactivation significantly improved energy usage and/or movement performance.
• A simple function based on decoded speed and its derivative effectively controlled coactivation levels.
• The multi-table method demonstrated enhanced reaching capabilities compared to fixed coactivation.

Conclusions:

• Modulating muscle coactivation during brain-controlled FES is a viable strategy to improve energy efficiency and movement performance.
• This approach enhances the potential of FES for restoring reaching function in individuals with paralysis.
• Dynamic control of limb stiffness offers a more adaptable and efficient FES system.