There is an increasing need for transfemoral prostheses that provide gait support, stability, safety and comfort. Although there are many prostheses available in different levels of complexity and price, there is still room for improvement. It has been proved that the cost of transport (CoT) for walking is significantly increased for transfemoral amputees with respect to their healthy peers. Assisting push-off is one of the main challenges in prosthesis design. Push-off is normally achieved by plantarflexion of the ankle joint. Prosthesis designs should aim to restore this function in order to lower the amount of energy needed for walking.

This study aims to investigate the effect of prosthesis design on the gait pattern through musculoskeletal modelling and predictive simulations. Two prosthesis designs are modelled for these purposes, after which several variations on these models are made. It is hypothesised that the prosthesis that assists in push-off through ankle plantarflexion, should result in a gait pattern that is closer to a healthy one. It should also decrease the CoT. Furthermore, we aim to evaluate the use of modelling and simulations in the customisation of prostheses.

OpenSim was used to create a total of eight models based on a model with 9 degrees of freedom and 18 muscles: a healthy person, a conventional prosthesis model, two scaled versions of the conventional prosthesis model, the walkMECH prosthesis and three variations on the walkMECH. SCONE was used to find an optimal gait pattern for each of the models through the CMA-ES method. CoT-, gait-, degrees of freedom- and reaction force objectives were minimised. The results were evaluated by comparing the CoT, joint angles, ground reaction forces and muscle activation of each model.

The CoT for the healthy model was found to be higher than reported before, based on both experimental and simulation studies. As a result, we have little confidence in the CoT estimation of our models. This is further exacerbated by the finding of a lower CoT for the conventional prosthesis than for the healthy model, in contrast to earlier reports. The results for most other measures were irregular, making it difficult to draw conclusions from them. It is expected that the predictive optimisations did not reach a global minimum, and that the results are therefore not accurate. Future research should aim to solve this problem. It should also be attempted to find the cause of the difference in CoT between our simulations and those of others.

No conclusions could be drawn from the results. Nonetheless, there is a clear potential for the use of musculoskeletal modelling and predictive simulation in the investigation of the effects of prosthesis design on gait.

Paralympic sports are growing more popular. Besides the dedicated training of the athlete, technology is crucial to empower amputees to perform at their highest level. The recent carbon fibre Running-Specific- Prosthesis (RSP) have energy stored and return capabilities that allow runners with amputations to perform almost as able-bodied. However, due to the difference in power output between a biological ankle and a RSP, unilateral transtibial (UTT) amputees need to adjust their biomechanics to an asymmetric pattern. It is known that the stiffness of the blade has a great influence on the performance of the athlete. The main challenge was to find a method to prescribe the optimal stiffness for a particular athlete, that allows him/her to performthe best in a race. The current approach to advice a RSP is based on the bodyweight of the athlete and the coaches and athletes wishes. Nevertheless, as a result of the insufficient number of subjects and the difficulty to performa randomised control trial, there is limited evidence about the UTT athlete capability of adapting their muscle activity to different prosthesis stiffness and the optimal RSP stiffness for them. In order to investigate this, two main goals for this master thesis project were raised: to implement a musculoskeletal model of an UTT amputee athlete wearing a RSP and predict its optimal running biomechanics through predictive forward dynamic simulations; to find the optimal athlete-RSP stiffness combination that maximizes the running performance. Five different stiffness of a Flex-Run ¨Ossur (Reykjavík, Island) RSP were modelled and simulated for the maximumvelocity the model could reach. Results: firstly, the model could perform better with a middle-class RSP category. It enhanced the hip muscles to exert more power in the blade during the first part of the stance phase. However, the prosthetic leg generated 41.2% lower total average power, including the RSP power, than the intact leg. The RSP made up 24.8% of the total prosthetic leg power. Secondly, the intact leg benefited from an improved push-off of the prosthetic leg having a favourable landing that allowed to exert more power and propel the body into longer flight time than with low-class RSP categories. Still, the top speed of the model was far from what athlete can achieve, but the motion and kinetic data were comparable for low running speeds. Therefore, it could be concluded that a reasonable prediction of the optimal RSP stiffness for running at about 4.6 m/s was achieved. The presented biomechanical model could potentially be used to assist coaches and athletes to have a better idea of themost suitable RSP stiffness.