I would like to thank thesis my directors José Luis Pons Rovira, Eduardo Rocon de Lima and Juan Camilo Moreno Sastoque. Furthermore, I would also like to thank my tutor Sira Elena Palazuelos Cagigas for her extraordinary guidance, advice, and for helping me develop the present work. Especially thanks to Juan and Eduardo, who never give up on me and insisted carry on at moments when finishing seemed impossible. Also, I would like to thank Fernando, without him this thesis wouldn´t had been finished. He stood by me and provided me with the necessary equipment for my work. I would like to thank Soraya and all the staff of the biomechanical laboratory of the National Paraplegic Hospital in Toledo for their contribution to the design, development, and performance of the evaluation studies with patients. Finally, I appreciate all the subjects and patients that participated in this study without them, nothing would have been possible