Experimental studies of the behavior of the human body exposed to vibration serve as the basis for the development of mechanical models. The problem of uniqueness of model parameters is of key importance when the model is used to create effective vibration protection systems. This paper examines the possibility of obtaining a unique set of model parameters when there are experimental data as an amplitude-frequency characteristic or the absolute value of the input mechanical impedance. Using a three-degree-of-freedom model as an example, we have demonstrated that this problem does not have a unique solution in the general case. We have elucidated additional experimental data required to ensure that the solution is unique.