Biomedical Engineering Reference
In-Depth Information
Fig. 8.4
The detailed 3D FE model and the geometrically simplified upper limb model
(DOF) musculoskeletal system. The first musculoskeletal model consists of three-
dimensional continuum-mechanical models of the biceps brachii and triceps brachii
(including its tendons) as an antagonistic muscle pair, the humerus, radius and ulna
as three-dimensional rigid representations of the involved bones, and the elbow joint
as a one-DOF hinge joint. The prediction for the position of the radius and ulna
stems from the 1-DOF-model depicted in Fig.
8.4
.
8.6 Discussion
The strength of the electromechanical model is certainly its modular composition
and flexibility. Any part of the model can be replaced by newly developed more
sophisticated models, which for example describe the electrophysiology on the cel-
lular level, the motor unit recruitment algorithm, or the continuum-mechanical con-
stitutive equation. Furthermore, the framework can be extended to include further
models, e.g., models of muscle spindles or Golgi tendon organs, or to incorporate
afferent input in the MU recruitment model. Further, different neuro-physiological
models, in particular models that are based on system-biological approaches like
Cisi and Kohn (
2008
) can be investigated in much more detail. Understanding the
recruitment principles of single muscles and within a musculoskeletal system en-
hances the applicability of the forward-dynamics simulations based on continuum-
mechanical models.
In its current form, however, the electromechanical model also contains a number
of weaknesses. Currently, some of the integrated models stem from models derived
for different species. For example, the geometrical model is based on the human
TA muscle while the electro-physiological model of Shorten et al. (
2007
) has been
validated on mouse muscles. Moreover, when coupling different models, the number
of parameters to be determined beforehand increases. The model of Shorten et al.
(
2007
) by itself contains more than 50 ODEs and even more parameters. For many
of these values and parameters of the other models, in particular on the motor unit
distribution, only few data are available from the literature.
