The present work had two objectives : On the one hand, to provide a triple methodological contribution to the analysis of motor coordination. Firstly, this contribution consists in analysing the sensibility of an inverse dynamics procedure to the quality of the anthropometric input data. A recommendation for the use of a BSP estimation method was provided to compute the net joint moments in a better way. Secondly, an evolution of a biomechanical model that includes the kinematics, BSP, groud reaction and EMG as input data into a numerical optimization process was proposed to estimate the moments developed by the knee flexor and extensor muscle groups under muscle fatigue condition. The loss of force production capacity due to fatigue was taken into account in the numerical procedure by means of a frequency analysis of the EMG signal. The spectral analysis was carried out using wavelet transform. Thirdly, a procedure was developed to estimate the individual muscle tension with an optimal prediction of the co-contraction. On the other hand, an analysis of the muscular coordination was carried out during squat exercises when faced with either an internal or an external perturbation. The external perturbation results from supplementary loads added to the subjects while muscle fatigue of the agonist muscle group qualified the internal perturbation. Our results show an exploitation of the muscle redundancy both to stabilize the joint and to produce coordinated motions. Moreover, the exploitation of the muscle redundancy in presence of fatigue differs from that observed when adding load. Thus, the Central Nervous System exploits differently, but always in an optimal sense, the muscular redundancy when faced with a perturbation.