Original ArticlesPrediction of muscle force involved in shoulder internal rotation*,**
Section snippets
Methods
The function of shoulder internal rotation in static equilibrium conditions (maximum voluntary isometric contraction) was used. Internal rotation of the shoulder was defined as internal rotation about the longitudinal axis of the humerus (Figure 1).The position of 90° elevation in the coronal plane was chosen for this simulation, because this position is crucial for the functional activities of daily life and overhead throwing in
Results
The predicted muscle stress was 114.14 N/cm2 (Table I).Muscle stress RMS error for training samples RMS error for testing samples 114.14 7.5 7.7 RMS, Root mean square.
The distribution of muscle force was
Discussion
EMG-driven models can predict physiological phenomenon such as co-contraction better than optimization-based models, because the input data are derived from a measure of muscle activation. This study extended the application of Monte Carlo simulation from analyzing the effects of parameter variability in optimization models of the shoulder to analyzing these effects in an EMG-driven model.
To quantitatively capture the variability of the shoulder muscle force for the function of internal
Acknowledgements
We thank Dr. Guillaume Herzberg for providing the original data of physiological cross-sectional area for shoulder muscles.
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Supported by National Institutes of Health grant AR 41171.
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Reprint requests: Kai-Nan An, PhD, Orthopedic Biomechanics Laboratory, Mayo Clinic/Mayo Foundation, Rochester, MN 55905 (E-mail: [email protected]).