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Elastic- and viscous-like properties of the upper arm estimated by the indentation method

The purpose of this study is to estimate the elastic-and viscous-like properties of the human upper arm using the indentation method. Healthy male subjects put their upper arms horizontally on a table. An indenter was placed 1-2 mm over the upper arm. When the indenter was moved vertically with a robot arm, the displacement of the indenter and the force were measured. First, the relationships between the displacement and the force were modeled using several variations on the non-linear Voigt model. The model based on Herz's theory did not provide a good approximation of the indentation responses, but the proposed model did. Next, the indentation point dependency of the upper arm was investigated. The muscle hardness (elasticity and viscosity) was invariant in a relatively large area of the upper arm. Finally, the elastic and viscous coefficients of the upper arm were estimated when the subject was holding a weight. The heavier the weight was, the larger the elastic and viscous coefficients were. The results suggest that the muscle hardness can be evaluated quantitatively with the elastic and viscous coefficients estimated by the proposed model.