The article presents an analysis of experimental studies of the human body behavior under vibration. The results of these studies are the basis for the construction of the human body mechanical models, which are used in the construction of vibration protection systems. The main attention is paid to solving the problem of determining the mechanical model parameters and solving the problem of the uniqueness for this problem solution. Deciding on a single set of model parameter values is crucial to creating a vibration protection system. Unfortunately, this problem has not been investigated before. In this regard, the possibilities of obtaining a unique solution having available the experimental seat-to-head transmissibility or modulus of the input mechanical impedance have been studied. On the example of mechanical models with two degrees of freedom, it has been shown that in general this problem has no unique solution. In addition, for each type of experimental results it was established what additional experimental data were you need to get for the problem to have a single solution. In particular, it is necessary to know not only the transmission from the seat to the head but also the transmission from the seat to each part of the model.