Predicting muscle forces in the shoulder by constraining the inverse optimisation with EMG and a forward muscle model

Abstract

The Dutch Shoulder and Elbow Model (DSEM) is a musculoskeletal model of the shoulder that can be used to predict internal shoulder loading (muscle forces, joint reaction forces, etc.). The DSEM uses an inverse optimisation method to predict muscle forces from net joint moments. In this study two new modes are presented that constrain the inverse optimisation with muscle force boundaries based on muscle dynamics (inverse forward dynamical mode) and boundaries based on EMG-recordings (EMG-assisted mode). The new modes were validated with measurements of two standardised movements (abduction and ante exion) from two subjects. A proof of concept has been given that both new modes work. It was concluded that DSEM predictions can be dominated by morphological differences between the subject and the cadaver on which the DSEM is based. Until better scaling routines are developed the IFDO mode is not very useful. When EMG-constraints are added, muscle and GH-joint reaction forces are predicted to be higher. Adding EMG for one muscle can predict cocontraction in other muscles. By adding EMG-based constraints, the DSEM can account for individual strategies in control strategy for the data that was analysed and is therefore an interesting topic for future research.