The goal of the works presented in this paper is to study the feasibility of the in-vivo estimation of the musculo-tendon dynamics using an original approach. Contrarily to usual literature in this field the Hill-Stroeve based model parameters are estimated, and not only some global parameters with little physiological meaning. This estimation is based on the computation of the inverse kinematics and the inverse dynamics of the human body, using a musculo-skeletal description. It also includes an optimization of the muscle force. Muscles are described by a modified and simplified Hill-type model. Parameters involved in this model are estimated in-vivo. In the preliminary works the flexion-extension of the elbow joint only is considered. Experimental set-up includes EMGs acquisition and motion capture data. Movements are chosen to limit cocontraction of antagonist muscles. Results are given for three of four muscles involved in the joint movements. Such results are very important for medical applications in rehabilitation, sport science, study of muscle diseases