Agonist-Antagonist Neural Coordination without Mechanical Coupling after Targeted Muscle Reinnervation

TL;DR

This study shows that after targeted muscle reinnervation, the central nervous system maintains coordinated control of agonist and antagonist muscles at the motor unit level, despite the loss of natural mechanical coupling.

Contribution

It provides the first evidence at the motor-unit level that CNS preserves agonist-antagonist coordination post-TMR, informing future surgical and prosthetic strategies.

Findings

Over 40% of motor units active during agonist tasks are also recruited during antagonist tasks.

Motor units show different firing rates depending on their functional role.

CNS preserves agonist-antagonist coordination despite altered mechanical coupling.

Abstract

Following limb amputation and targeted muscle reinnervation (TMR), nerves that originally innervated agonist and antagonist muscles are rerouted into one or more residual target muscles. This rerouting profoundly alters the natural mechanical coupling and afferent signalling that normally link muscle groups in intact limbs. Despite this disruption, in this study we demonstrate, using high-density intramuscular microelectrode arrays implanted in reinnervated muscles of three TMR participants, that motor units (MUs) associated with agonist and antagonist tasks remain functionally coupled. Specifically, over 40% of motor units active during agonist tasks were also recruited during the corresponding antagonist tasks, even though no visual feedback on antagonist neural activity was provided. These motor units exhibited significantly different firing rates depending on their functional role. These results provide the first motor-unit-level evidence that the central nervous system preserves coordinated agonist-antagonist control after TMR and inform restorative surgical strategies and prosthetic systems capable of regulating both limb kinematics and dynamics based on agonist-antagonist commands interplay.