Restoration of Normative Postural Control

Lab Visit Experience for Participants with lower limb amputation: * Number of Lab Visits: 15 visits. Clinicians may recommend skipping some of the visits or tasks based on clinical evaluation and status of the participants. * Length of Lab Visit: three hours maximum 1. First visit: the purpose of the first visit is to conduct consent and conduct measurements to decide walking speed and ABC (amputee balance confidence) score. 2. Second visit: this visit is to ensure that the amputees' own socket system can be integrated into the powered prosthetic leg and validate the effectiveness of the EMG interface. 3. Third and fourth visits: baseline evaluation with powered prosthesis and passive prosthesis. Each participant will finish the two visits. One of the visits is dedicated to their own passive prosthesis and the other visit is for the powered prosthesis. The sequence of the evaluation is randomized. The tasks conducted in the two visits are generally identical. The only difference is that one of the visits uses the participants' everyday prosthetic foot and the other uses the powered prosthetic ankle 4. Fifth and sixth visits: these visits are dedicated to have the participants trained to regain muscle coordination, which is critical to use the powered prosthetic ankle. All the participants will go through these trainings. Based on whether the participants are selected as the powered prosthetic group (Group A) or the passive group (Group B), the participants will finish this training with the powered prosthetic leg or a passive prosthetic leg. 5. Seven - eleventh visits: These visits are designed to give participants needed training, so participants are able to integrate the action of the powered prosthetic ankle with their full body motion for various tasks. To ensure that contribution of the training procedure to the performance changes are considered, all the participants will go through the training with the prostheses aligned with their group. 6. Twelfth-thirteenth visit (duplicate of Third and fourth visit). These visits are used to evaluate the impact of the training program on the performance of the participants to conduct tasks which are not included in the training procedure. Each participant will conduct the task with both passive and powered prosthetic legs on different days. 7. Fourteenth-fifteenth visits (duplicate of Third and fourth visit). These visits are used to understand the long term effects of the training program on the participants. These visits will be conducted three months after the 13th visits.