This study proposes in vivo tests and design of experiments to determine the influence of experimental factors on the mechanical response of the soft tissue. The experimental factors considered are: room temperature (A), indentation velocity (B), indenter temperature (C), pump pressure (D) and muscle activation (E). An inverse method was developed to obtain the constants for constitutive equations of a multilayer biological model (skin, hypodermis, and muscle) through the use of indentation tests in combination with a finite element method. For each combination of the experimental factors, two groups of constants were established from the inverse method. Sixteen combinations of experimental conditions and their corresponding constants for the Mooney-Rivlin constitutive equations were obtained to be used in further numerical models. The factor D and factor interactions ADE, CDE, and ACDE were statistically significant with respect to skin mechanical response. Therefore, it can be concluded that there is not a current equation able to represent the mechanical properties of the skin under all the experimental conditions considered in this study.