ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

Figure 1: A three-step process simulation to compute joint loads and muscle forces from a
musculoskeletal model of the hand and forearm.
- Firstly, an accurate musculoskeletal model of the hand and forearm has been
designed under the LifeMOD simulation software (MSC Software Inc., Santa
Ana, CA, USA). The model is composed of 21 segments, 21 joints providing 26
degrees of freedom, and 46 muscle units.
- Secondly, motion capture data are imported in the modeling software.
Kinematical data have been recorded during three manual tasks: a maximal
grasping task, a maximal pressing task for digit 3 and a disk gripping task. An
optoelectronic system (VICON, Oxford Metrics Ltd, Oxford, UK) was used to
track the position of passive markers in three dimensions. This system is
composed of 7 infrared cameras with a resolution of 16 megapixels which
recorded the position of 43 reflective markers of 3 mm-size attached to different
bony landmarks on hand and forearm segments. During these experiments, EMG
acquisitions of flexor digitorum superficialis (FDS) and extensor digitorum
communis (EDC) have been performed. Moreover, a manual dynamometer
enabled to record external forces during maximal grasping and pressing tasks
(see Fig. 2).
Figure 2: Manual tasks recorded during motion capture experiments: maximal grasping
(a), disk gripping (b) and maximal pressing (c).
- Thirdly, an inverse-to-forward dynamics simulation is run. Based on real
kinematical data, the inverse dynamics simulation is firstly done to drive the
model whereas the trainable elements in joints and muscles record joint
angulations and muscle-contraction histories. Then these recordable elements
are replaced with trained active elements in a subsequent forward dynamics
simulation based on proportional derivative servo controllers. During the
simulation, contact forces are also computed using an ellipsoid-plate contact