During the everyday life, our articulations are subjected to numerous different static and dynamic effects, in the structure of the human body they ensuring the proper attachment between the articulating bones. Within them, the various ligaments take care of the stability of the joints, their healthy functioning is essential even for ordinary daily activities. Due to the extremely serious consequences of their damage or rupture, medical science has aimed to find an adequate way to heal or replace them with natural or artificial tendons/ligaments, but so far (mostly the long term) results are not satisfactory at all. For the improvement of these procedures the better understanding and description of their mechanical behaviour is necessary. Our articulations (knee, ankle, hand and shoulder) show very difficult mechanical behaviour both from the point of loading conditions and material behaviour. Thus, the trustworthy numerical simulation of them is a very complex problem, on the top of the irregular geometry, both geometrical and material nonlinearities have to be taken into account. That is why real laboratory experiments are indispensable for the reliable numerical results. For this purpose, series of experiments have been performed on tendons and ligaments in the Biomechanical Laboratory of the BUTE. By the evaluation of the results different hyperelastic material models are parameterized and compared with the help of simple finite element models. On the basis of these models a three-dimensional numerical model is developed in Ansys, validated by real and numerical results. On this model, frequently occurring motions are investigated, focusing on the mechanical response of the major knee joints.