# A continuum model of skeletal muscle tissue with loss of activation

## TL;DR

This paper develops a continuum hyperelastic model for skeletal muscle tissue that incorporates aging-related loss of activation, using experimental data fitting and the active strain approach to simulate sarcopenia effects.

## Contribution

It introduces a novel continuum model that accounts for muscle activation loss due to aging, combining experimental data fitting with the active strain approach.

## Key findings

- Model captures reduced muscle activation in aging.
- Numerical simulations illustrate effects of activation loss.
- Model provides a framework for studying sarcopenia.

## Abstract

We present a continuum model for the mechanical behavior of the skeletal muscle tissue when its functionality is reduced due to aging. The loss of ability of activating is typical of the geriatric syndrome called sarcopenia. The material is described by a hyperelastic, polyconvex, transverse isotropic strain energy function. The three material parameters appearing in the energy are fitted by least square optimization on experimental data, while incompressibility is assumed through a Lagrange multiplier representing the hydrostatic pressure. The activation of the muscle fibers, which is related to the contraction of the sarcomere, is modeled by the so called active strain approach. The loss of performance of an elder muscle is then obtained by lowering of some percentage the active part of the stress. The model is implemented numerically and the obtained results are discussed and graphically represented.