Transfemoral prosthesis users typically perform the sit-to-stand motion unilaterally, placing minimal load on the prosthetic side. This increases the risk of injury and accelerates the degeneration of the intact limb. To address this, understanding compensation strategies is essential. Predictive neuromusculoskeletal modeling offers a method to investigate this. The aim of this study was to develop and validate a neuromusculoskeletal model with reflex-based muscle control to simulate the sit-tostand motion in non-amputees and transfemoral amputees with a passive prosthesis. We developed a three-dimensional sit-tostand musculoskeletal model of a non-amputee (20 degrees of freedom, 24 muscles) and a transfemoral amputee (20 degrees of freedom, 19 muscles), both incorporating a two-phase stand-up controller based on an existing two-dimensional reflex controller. We compared the simulation framework to measured kinematics, muscle activations, ground reaction forces, and existing literature on degrees of asymmetry and muscle forces. The developed framework was used to optimize prosthetic knee and ankle stiffness and damping for the sit-to-stand motion with a passive prosthesis. The simulated kinematics of the non-amputee matched measured kinematics. The prosthesis model indicated compensation strategies involving increased thoracic and lumbar extension, lumbar bending towards the non-amputated side,
increased pelvic tilt combined with decreased hip flexion, and heightened muscle activation and force. Optimization results suggested a knee stiffness of 0.1432 [Nm/deg] and damping of 0.0246 [Nm·s/deg], while the ankle required a stiffness of 0.1968 [Nm/deg] and damping of 0.1350 [Nm·s/deg]. These values are recommended for testing in future experiments.

Energy harvesting has gained lots of interest over the past few decades. This study explores the application of energy harvesting in lower limb prosthetic devices. The control system of a lower limb prosthesis includes sensors, wireless
systems and other active components which all require battery power. In order to save some of this battery power, reduce weight, and have the devices have a longer runtime, a form of energy regeneration is desired. Therefore the goal of
this study is to design and experimentally evaluate an energy harvesting system to power the control system of lower limb prostheses. The final prototype is designed following the process of setting up functional requirements, constraints and wishes. This leads to three derived concepts. After an evaluation against performance criteria and an in-depth evaluation concerning the power output, the compliant spring design is chosen to be worked out further and evaluated with a newly designed vibration shaker table. The relevant findings are laid out in the results. From these findings, interpretations and implications are discussed further, concerning advantages and limitations of the energy harvesters and the experiment. Results from the conducted experiment show a peak power output of 25.8 mW at an input amplitude of 12 mm and a frequency of 9 Hz. A power mass ratio of 0.21W/kg is achieved. The design meets the power demand requirements to power microprocessors and sensors of the control system of a lower limb prosthesis and extends runtime with 15.7%. However it is still important to investigate the power requirements for state of the art lower limb prostheses. Furthermore, it is recommended to improve overall efficiency in future studies, compare the results with state of the art energy harvesters based on vibrations, and execute a gait test for further design validation. The results from this study demonstrate comparable data and present the innovations possible in prosthesis design and the advancements in utilizing ambient power sources for energy harvesting. Enhancing the overall efficiency of this design, and promoting comparable results to other designs in the existing literature, could emphasize on the potential of energy harvesting applications.