Passive Mechanical Properties of Skeletal Muscle: Analyzing the Effects of Denervation with Mathematical Modelling in a Rabbit Quadriceps Model

Abstract

Background: The aim of the study was to analyze the effects of denervation on skeletal muscle in-vitro passive mechanical properties utilizing a fraction- al order viscoelastic material model.
Methods: 24 New Zealand rabbits were grouped into two; control group (n = 8) and denervation group (n = 16). In-vitro passive mechanical tests were performed on healthy and denervated quadriceps muscles. Relaxation and creep test curves were fitted with the best fitting curve of the ‘three-element fractional viscoelastic material model’. Following this eight material param- eters characterizing the passive mechanical material properties were extract- ed for each specimen (E1, E2, τ, βr, 1/E1, 1/E2, η and βc).

Results: The fractional order viscoelastic model demonstrated good curve-fitting to the experimental data and least square error values were found to be below 1%. There were statistically significant differences in two parameters for stress relaxation. Firstly, denervated skeletal muscles demon- strated a more solid material behavior in stress relaxation tests (βr) (p = 0.042). Secondly, healthy muscles were relaxed significantly faster than denervated ones (τ) (p=0.017). There was no significant difference between groups in creep tests.

Conclusions: Denervation altered some in-vitro stress-relaxation properties of the skeletal muscles but did not affect creep performance. The effects of pathological conditions in the passive mechanical properties of skeletal mus- cle can be analyzed with fractional order viscoelastic material models.