A MODEL PREDICTING INDIVIDUAL SHOULDER MUSCLE FORCES BASED ON RELATIONSHIP BETWEEN ELECTROMYOGRAPHIC AND 3D EXTERNAL FORCES IN STATIC POSITION

To study the potentiality for developing an EMG-based model for the hu man shoulder, mapping of relations between static hand forces and elec tromyographic (EMG) activity of 13 shoulder muscles, were performed. T he procedure was to perform by the hands slowly varying isometric forc es up to 20% maximum voluntary force in the three-dimensional space. B y combining these data with literature values on muscle physiological cross-sectional area and moment arm data, an EMG-based model was devel oped for estimating muscle forces in the glenohumeral joint. The model was validated for one standardized position by comparing joint moment , calculated from EMG by using the model, with moments from the extern al force. The highest correlation between these moments was found assu ming a linear EMG/force calibration at low force level( < 20% MVC), gi ving correlations from 0.65 to 0.95 for the abduction/adduction moment and from 0.70 to 0.93 for the flexion/extension moment, for the six s ubjects. Moments calculated from EMG were for most subjects somewhat l ower than the moments from the external force; the mean residual error ranged from 1.6 to 9.9 Nm. Taking this into account, the results can be used for assessment of muscle forces based on recordings of externa l forces at the hands during submaximal static work tasks without subs tantially elevated arms. (C) 1998 Elsevier Science Ltd. All rights res erved.