Biomedical Engineering Reference
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Fig. 8.5 a Biceps of a male subject supported in a test rig, b hysteresis force-displacement
curves of the stressed biceps at different external loads (i.e. muscle tensions)
soft tissue regions, as encountered in the seated or recumbent body position
( Chaps. 6 and 7 ). Under dynamic loading, such as during walking, running or
automotive crash, a different situation is encountered. Here, the muscles or muscle
groups, active during body motion, must be modelled as active elements. Aside
from adequate material equations employed for continuum mechanical description
of muscles (to date employing the contractive H ILL model, Hill (1938), which is
based on three rheological elements), appropriate in vivo experiments are essential
to determine the material functions. A feasible approach conducted by the authors'
group is to load (i.e. stress) selected (single) muscles in a defined way and at the
same time perform indentation experiments to generate force-displacement data.
''Material curves'', which parametrically depend on respective muscle tension can
thus be obtained. Figure 8.5 depicts characteristic biceps loading and unloading
curves obtained from a male subject at eight different external loads (i.e. muscle
tensions), (Wrobel 2011) and (Sachse 2012).
8.5 Micro-Mechanical Modelling of Adipose Tissue
The mechanical characterization of human tissue material in Sect. 5.2 is based on a
phenomenological description, whereby the material is treated as a continuum. The
tissue deformation is described on the macroscopic level and the material is
regarded as uniformly or continuously distributed. The discontinuous character of
the tissue on the microscopic level is ignored.
The source of certain empirical observations, however, such as the blocking or
''lock-up'' effect when adipose tissue is compressed, as described in Sect. 5.2.2.3
and reported by (Comley and Fleck 2010), cannot be explained with the previously
described approach. One feasible approach to gain insight into such an effect is
modelling the material with non-classical continuum models (C OSSERAT - and/or
gradient theories) which can represent the inhomogeneous continuum element as a
continuum again. However, this approach has the disadvantage that additional
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