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

models have been developed. Because of the complexity and the redundancy of
anatomical structures of the hand and forearm, several sophisticated musculoskeletal
models of substructures have been suggested (Sancho-Bru et al., 2001; Valero-Cuevas
et al., 2003; Vigouroux et al., 2009; Wu et al., 2009). However, some researchers have
also designed biomechanical models that take into account the whole complexity of the
musculoskeletal system of the hand and forearm (Albrecht et al., 2003; Tsang et al.,
2005; Chalfoun et al., 2005; Li et Zhang, 2009; Johnson et al., 2010). More recently a
complete musculoskeletal model of the hand and forearm composed of 21 segments, 20
articulations (providing 24 degrees of freedom) and 46 muscle units has been developed
and used to estimate muscle forces and joint loads during a cylinder manual task
(Vignais et Marin, 2011).
However, one the main problem with musculoskeletal modeling is the lack of studies
reporting successful validation of internal parameters estimates. Musculoskeletal
validation processes depend on the biomechanical modeling approach. Firstly, the
inverse approach estimates muscle force by using external force data combined with
inverse dynamics and static optimization (Tsirakos et al., 1997). Muscle forces
estimated are typically compared to EMG activity patterns to validate results of this
approach. More precisely, the optimization technique used for the investigation of
muscle behaviour of the upper extremity is based on minimizing sum of squared muscle
forces. Secondly, in the forward approach, an initial set of muscle activations are fed
into a forward dynamics model of the musculoskeletal system to estimate the produced
movement. Then the solution is compared against experimental data and the process is
iterated by updating the muscle activations that best reproduce the experimental
kinematics (Erdemir et al., 2007). Thus the validation process of models based on the
forward approach is commonly assessed by its performance while tracking experimental
data (kinematics, kinetics, EMG). Concerning estimation of muscle forces, the
validation is solely based on comparing EMG data with estimated muscle activation
patterns.
The purpose of this study is therefore to design a validation process for a
musculoskeletal model of the hand and forearm based on experimental data. This
process will be performed at two levels: the first will deal with muscle activation
patterns comparison and the second will concern external forces comparison. A
calibration process will be proposed based on results from the validation process.
3. MATERIALS AND METHODS
3.1 Musculoskeletal modeling of the hand and forearm
In order to model the musculoskeletal model of the hand and forearm, a three-step
process has been developed (see Fig. 1):