Fig. 1.

Conceptual illustration of the AMI. Mechanical linkage of innervated muscles restores natural contracture-stretch relationships, leading to activation of native mechanoreceptors and bi-directional communication with the central nervous system. AMI function is described as follows: at rest, both AMI muscles are at resting length and tension. When the agonist muscle contracts under volitional or reflexive activation, the antagonist is passively stretched, causing increased spindle discharge in the antagonist. This spindle activity is interpreted by the central nervous system (CNS) as a change in phantom joint position. Force feedback is provided to the CNS as artificial stimulation of the antagonist muscle causes it to contract in opposition to the agonist, creating tension at the agonist musculotendinous junction and increasing agonist Golgi tendon organ (GTO) discharge. This is interpreted by the CNS as torque about the phantom joint. A representation of muscle spindle and GTO state is shown for each condition.