M.J. Muñoz

A 3D active-passive numerical skeletal muscle model incorporating initial tissue strains. Validation with experimental results on rat tibialis anterior muscle

This paper presents a three-dimensional finite element model of skeletal muscle and its validation incorporating inital tissue strains. A constitutive relation was determined by using a convex free strain energy function (SEF) where active and passive response contributions were obtained fitting experimental data from the rat tibialis anterior (TA) muscle. The passive and active finite strains response was modelled within the framework of continuum mechanics by a quasi-incompressible transversely isotropic material formulation. Magnetic resonance images (MRI) were obtained to reconstruct the external geometry of the TA. This geometry includes initial strains also taken into account in the numerical model. The numerical results show excellent agreement with the experimental results when comparing reaction force-extension curves both in passive and active tests. The proposed constitutive model for the muscle is implemented in a subroutine in the commercial finite element software package ABAQUS.

Determination of passive viscoelastic response of the abdominal muscle and related constitutive modeling: Stress-relaxation behavior

In this paper, the authors investigate the passive viscoelastic properties of rabbit abdominal wall. In vitro strain relaxation tests were performed in the oblique muscle (in two perpendicular directions), the rectus abdominis and the linea alba in the longitudinal direction. Based on experimental data, a model for the viscoelastic mechanical properties of this tissue is presented here. In particular, we used a 3D non-linear viscoelastic model to fit data sets obtained from tissue of the rabbit abdominal wall. Uniaxial relaxation tests were carried out for samples obtained from the abdominal wall. The experimental results clearly demonstrate the anisotropy and nonlinearity of the abdominal tissue. The stress relaxation was higher in the transverse direction (closer to muscle fibers) with an average value of the final stress ratio of 48%, than in the longitudinal direction with around 56% of this ratio for the oblique muscle. These tests, at several stretch levels, presented a different behavior depending on the region where the tissue sample was located. There was no dependence between the stress relaxation ratio and the stretch level for the oblique muscles in their longitudinal or transverse directions (p>0.01). In contrast, for rectus abdominis and linea alba a dependence between the stress relaxation ratio and stretch level was found. Our study revealed an increase in the stress relaxation ratio for the rectus abdominis (p<0.01) and a decrease for the linea alba with higher stretch levels (p<0.01). Overall good predictions ε<0.115 were obtained with the model proposed for the oblique muscle (no dependence on the stretch level) and to reproduce the non-linear viscoelastic response of rectus abdominis and linea alba.

On simulating sustained isometric muscle fatigue: a phenomenological model considering different fiber metabolisms.

The present study shows a new computational FEM technique to simulate the evolution of the mechanical response of 3D muscle models subjected to fatigue. In an attempt to obtain very realistic models, parameters needed to adjust the mathematical formulation were obtained from in vivo experimental tests. The fatigue contractile properties of three different rat muscles (Tibialis Anterior, Extensor Digitorium Longus and Soleus) subjected to sustained maximal isometric contraction were determined. Experiments were conducted on three groups

On Using Model Populations to Determine Mechanical Properties of Skeletal Muscle. Application to Concentric Contraction Simulation

(n=5)

Oxidative stress prediction: A preliminary approach using a response surface based technique

(n=5) of male Wistar rats

Caracterización de la fatiga muscular en músculos con diferente metabolismo fibrilar. Un estudio experimental in vitro

(313 pm 81.14,hbox {g})