Abstract
Ensuring glenohumeral stability during repetitive lifting tasks is a key factor to reduce the risk of shoulder injuries. Nevertheless, the literature reveals some lack concerning the assessment of the muscles that ensure glenohumeral stability during specific lifting tasks. Therefore, the purpose of this study was to assess the stabilization function of shoulder muscles during a lifting task. Kinematics and muscle electromyograms (n = 9) were recorded from 13 healthy adults during a bi-manual lifting task performed from the hip to the shoulder level. A generic upper-limb OpenSim model was implemented to simulate glenohumeral stability and instability by performing static optimizations with and without glenohumeral stability constraints. This procedure enabled to compute the level of shoulder muscle activity and forces in the two conditions. Without the stability constraint, the simulated movement was unstable during 74%±16% of the time. The force of the supraspinatus was significantly increased of 107% (p<0.002) when the glenohumeral stability constraint was implemented. The increased supraspinatus force led to greater compressive force (p<0.001) and smaller shear force (p<0.001), which contributed to improved glenohumeral stability. It was concluded that the supraspinatus may be the main contributor to glenohumeral stability during lifting task.
Highlights
The glenohumeral joint enables the greatest articular mobility in the human body at the expense of its stability [1,2,3]
Glenohumeral instability may be caused by an external contact, internal forces produced by the muscles surrounding the humeral head may result in glenohumeral instability
To the best of our knowledge, this study is the first that evaluated the contribution of shoulder muscles in glenohumeral stability during dynamic movement such as a lifting task
Summary
The glenohumeral joint enables the greatest articular mobility in the human body at the expense of its stability [1,2,3]. Clinical instability is usually defined as any translation of the humeral head [4, 5] while, from a biomechanical point of view, glenohumeral joint instability occurs when the resultant glenohumeral reaction force points outside the glenoid surface [6]. Escamilla et al [8] pointed out that the activation of the anterior deltoid may cause a translation of the humeral head and reduce the stability of the glenohumeral joint. Movements such as lifting task for which middle and anterior deltoids are the main prime movers [9, 10] may be subject to glenohumeral instability
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