Abstract
The purpose of the present study is to establish a method to estimate viscoelasticity of muscle, subcutaneous tissue and skin by using mechanical stimulation. Six healthy male subjects participated in the experiment. The tibialis anterior muscle in voluntary isometric contraction was stimulated with a vibrator. The driving force(f), the vibrator acceleration(a), and the acceleration on the skin(y) were detected with an impedance head close to the muscle belly, and two acceleration sensors attached on the skin of 2 cm proximal and distal site of the muscle belly. The frequency response function between f and a, G(ω), biomechanical impedance, and the frequency response function between a and y, H(ω), were calculated. The undamped natural frequency, which mainly reflected the elasticity, was calculated as the frequency at which the real part of G(ω) or H(ω) become equal to zero. Effective vibration mass, elastic modulus, viscous modulus, and damping factor were estimated by approximating the frequency response function to that of a mass-damper-spring model with the nonlinear least square method. The undamped natural frequency of G(ω) increased as the contraction level increased, while that of H(ω) did not. The function G(ω) dominantly reflected the muscle characteristics because the vibrator was forced into the skin. The elastic modulus of the muscle increased, and effective vibration mass and viscous modulus did not increase, and damping factor decreased as the contraction level increased. At 2 cm proximal or distal site, the subcutaneous tissue and the skin had a dominant effect because they were the propagating medium of the vibration. In conclusion, viscoelasticity of the muscle, the subcutaneous tissue and the skin could be estimated with G(ω) and H(ω), respectively.
