## RE: Muscle's curve

Nashwa Abdel Baki writes:

>I'm looking for the stress-strain curve and other parameters defining
>the characteristics of muscles. As I know it is defined as a nonlinear
>viscoplastic material. Could any one help me?. I would appreciate any reply.

You do not say whether you are interested in the properties of passive,
or of activated muscles. One way to describe the constitutive behaviour of
activated muscle (which in a certain sense is indeed visco-plastic) is:

F = u(t)f(L)g(dL/dt) + h(L),

with F the force being generated, u(t) the "active state" (normalized between
0 and 1), f(L) the force-length curve with its maximum at the maximal
isometric force and g(dL/dt) the force-velocity curve (Hill's equation), with
a maximum of 1 at dL/dt=0. h(L) represents the elastic properties of the
passive muscle (parallel elastic element). In case of no activity (u(t)=0),
only the second term remains, so this model may be too simplistic if you
are interested in passive muscle properties. Mathematical models for the
functions f,g and h can be found for example in several publications by
H. Hatze (e.g. A myocybernetic control model for skeletal muscle, Biological
Cybernetics 25:103-119 (1977) ).

The model may be further developed by adding a series elastic element,
in which case you obtain a first order differential equation.

Hope this information is helpful. I would also be interested in the opinions
of other BIOMCH-L subscribers.

Ton van den Bogert
Dept. of Veterinary Anatomy,
University of Utrecht, Netherlands.