Extraction of quasi-linear viscoelastic parameters for lower limb soft tissues from manual indentation experiment

A manual indentation protocol was established to assess the quasi-linear viscoelastic (QLV) properties of lower limb soft tissues. The QLV parameters were extracted using a curve-fitting procedure on the experimental indentation data. The load-indentation responses were obtained using an ultrasound indentation apparatus with a handheld pen-sized probe. Limb soft tissues at four sites of eight normal young subjects were tested in three body postures. Four QLV model parameters were extracted from the experimental data. The initial modulus Eg ranged from 0.22 kPa to 58.4 kPa. The nonlinear factor E, ranged from 21.7 kPa to 547 kPa. The time constant r ranged from 0.05 s to 8.93 s. The time-dependent material parameter a ranged from 0.029 to 0.277. Large variations of the parameters were noted among subjects, sites, and postures.