# Prosthesis Embodiment in Lower Extremity Limb Loss: A Narrative Review
## 4 Results
### Agonist-Antagonist Myoneural Interface
After calibrating a custom prosthesis capable of performing subtalar joint movements, subjects were asked to generate a specified torque while ascending or descending stairs. Participants with traditional amputations experienced the same motion reversals described in Section 2.1, whereas AMI amputees did not [50; 52]. Embodiment was also observed directly. Traditional amputees described the experiment as \"playing a video game for the first time\" and the prosthetic \"behaved in a way that was somewhat surprising\", while AMI amputees felt that the custom prosthesis was their leg and that a conventional prosthetic \"doesn't have the same animation to it\". [52]. AMI also enhances embodiment by enabling superior residual limb motor control compared to traditional amputation techniques that improve ownership and agency. Because AMI has high biomechanical fidelity, coordination between the AMI prosthesis and the contralateral limb is nearly indistinguishable from coordination between non-amputees' legs [50; 56]. In addition, the kinematics of the virtual limb is well-modeled by a model that represents the kinematics of the intact limb [56], indicating that the prosthesis \"feels\" and can be controlled like the native limb. This model could be used to create more personalized prosthetic devices that take into account scar tissue, other defects, and subject-specific perceptive responses [51]. Finally, for traditional amputees, activating the muscles associated with inversion or version of the virtual joint also activates the muscles associated with plantar flexion or dorsiflexion. However, the activation of unwanted muscles is less of a problem in amputees with AMI [21; 51]. In fact, amputees with AMI can also activate additional synergetic muscles to create a more natural, efficient, and controlled motion [51]. By reinstating natural agonist-antagonist muscle dynamics, AMI directly improves embodiment by restoring both proprioception and motor control. Enhancing these feedback mechanisms strengthens the user's sense of ownership and agency, enabling the prosthesis to feel and function like a natural limb. The AMI approach is still being improved to address notable drawbacks. In [21], patients with peripheral vascular disease were excluded from this study due to concerns about peripheral neuropathy. The graft harvesting process involved in AMI destroys capillaries and risks compromising the revascularization of the muscle [57], which may be a concern in patients with microvascular pathologies such as diabetes. Mild cellulitis was observed in two of the three subjects in [21], but this was resolved with oral antibiotics. A further drawback is that two-step procedures are necessary for proximal amputations, such as AKAs, because surgeons cannot immediately identify which sections of the remaining proximal sciatic nerve in the stump correspond to specific nerves that previously served the muscles of the distal lower leg [41]. As noted in Section 4.2, the main drawback of AMIis that the bandwidth to convey non-proprioceptive feedback is limited. This limitation motivates the cutaneous mechanoneural interfaces discussed in the next section.