Abstract
Glenohumeral stability is essential for a healthy function of the shoulder. It is ensured partly by the scapulohumeral muscular balance. Accordingly, modelling muscle interactions is a key factor in the understanding of occupational pathologies, and the development of ergonomic interventions. While static optimization is commonly used to estimate muscle activations, it tends to underestimate the role of shoulder’s antagonist muscles. The purpose of this study was to implement experimental electromyographic (EMG) data to predict muscle activations that could account for the stabilizing role of the shoulder muscles. Kinematics and EMG were recorded from 36 participants while lifting a box from hip to eye level. Muscle activations and glenohumeral joint reactions were estimated using an EMG-assisted algorithm and compared to those obtained using static optimization with a generic and calibrated model. Muscle activations predicted with the EMG-assisted method were generally larger. Additionally, more interactions between the different rotator cuff muscles, as well as between primer actuators and stabilizers, were predicted with the EMG-assisted method. Finally, glenohumeral forces calculated from a calibrated model remained within the boundaries of the glenoid stability cone. These findings suggest that EMG-assisted methods could account for scapulohumeral muscle co-contraction, and thus their contribution to the glenohumeral stability.
Highlights
The glenohumeral (GH) joint is the most mobile joint of the human body
Shear to compressive GH joint reaction forces predicted with EMGA remained within the stability cone boundaries, unlike those predicted with SO
The activations predicted by EMGA were more representative of rotator cuff muscles co-contractions, as well as co-contractions between the main GH actuators and stabilizers
Summary
The glenohumeral (GH) joint is the most mobile joint of the human body This mobility is enabled by the minimal congruence between the glenoid cavity and the humeral head, which compromises the GH stability. This stability requirement is largely met by the scapulohumeral muscular balance [1]. While rotator cuff muscles have been reported to act as the GH joint main stabilizers, all shoulder muscles contribute to the GH stability [3]. This intricate stability design puts the GH joint at a higher risk of dislocation, and its muscles at a higher injury hazard. The prediction of shoulder muscle interactions is a key factor in the development of ergonomic interventions
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