Paraplegic standing supported by FES-controlled ankle stiffness

Area of Science:

• Biomedical Engineering
• Neurorehabilitation
• Biomechanics

Background:

• Maintaining upright stance is challenging for individuals with spinal cord injuries.
• Functional electrical stimulation (FES) offers potential for restoring motor function.
• Upper body control plays a significant role in maintaining balance.

Purpose of the Study:

• To investigate if paraplegic subjects can achieve standing balance using upper body voluntary and reflex activity.
• To assess the efficacy of closed-loop controlled ankle stiffness via FES in supporting balance.
• To evaluate the contribution of FES-regulated ankle stiffness to balance maintenance.

Main Methods:

• A paraplegic subject was supported by a mechanical apparatus maintaining knee and hip extension.
• Training sessions focused on developing upper body balancing strategies with apparatus-supported ankle stiffness.
• Closed-loop FES was implemented to regulate ankle stiffness, replacing mechanical support.
• A method for controlling antagonist muscle moments was utilized.

Main Results:

• The subject successfully learned to use upper body movements for balance.
• Following FES implementation, the subject maintained balance without difficulty.
• Balance was lost when the FES support was removed.

Conclusions:

• Voluntary and reflex upper body activity, modulated by FES-controlled ankle stiffness, can enable standing balance in paraplegia.
• Closed-loop FES regulation of ankle stiffness is a viable method for balance support.
• The findings underscore the critical role of ankle proprioception and active stiffness in maintaining upright posture.