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Repetitive TasksRisk Assessment and Task Design
Published in R. S. Bridger, Introduction to Human Factors and Ergonomics, 2017
That the shoulder joint requires muscle activity to be held in place might alert the ergonomist to its likely susceptibility to rapid fatigue and damage when exposed to static loads or repetitive actions. One of the simplest ways to reduce occupationally induced shoulder stress in many jobs is to provide armrests, slings, or other means of supporting the weight of the arms to enable the shoulder muscles to relax. Whenever the hands or arms are used, muscle activity is necessary to keep the humerus in its socket and to hold the scapula in place on the thorax. The stabilizer muscles of the scapula are at a great mechanical disadvantage when the arms are held forward of the body (or cantilevered) and static muscle contractions are needed to resist the resulting moments. One of these muscles, the serratus anterior, acts to pull the scapula into the thorax. Excessive load or fatigue of this muscle may cause pain in the upper back. Damage to the serratus anterior can result in a condition known as a “winged scapula” where the scapula protrudes because it is no longer held close to the thorax due to muscle weakness. Carrying heavy rucksacks can damage the nerve supply to this muscle resulting in a condition known as “rucksack palsy.”
Activity of periscapular muscles and its correlation with external oblique during push-up: Does scapular dyskinesis change the electromyographic response?
Published in Journal of Sports Sciences, 2018
Rodrigo Cappatode de Araújo, André Luiz Torres Pirauá, Natália Barros Beltrão, Ana Carolina Rodarti Pitangui
Changes in the positioning and movement of the scapula have been conceptualised as scapular dyskinesis and associated with different shoulder disorders (Kibler et al., 2013). In order to fix and improve scapular function, it is suggested to strengthen the periscapular muscles (Ludewig et al., 2009). Some researchers have proposed the push-up as an alternative to strengthening these muscles, including inserting unstable surfaces, in order to increase the neuromuscular demand (Andrade, Araújo, Tucci, Martins, & Oliveira, 2011; De Araújo, De Andrade, Tucci, Martins, & De Oliveira, 2011; K.-M. Park et al., 2014). However, the advantages of performing such exercises on unstable surfaces are still uncertain (Behm & Colado, 2012).
Comparison of throwing kinematics and muscle activation of female elite handball players with and without pain – the effect of repeated maximal throws
Published in Sports Biomechanics, 2023
Tina Piil Torabi, Birgit Juul-Kristensen, Mogens Dam, Mette K Zebis, Roland van den Tillaar, Jesper Bencke
Furthermore, before maximal shoulder extension, the serratus anterior increased muscle peak activity after the FFP and after the maximal shoulder extension the muscle peak activity, decreased in both groups. Before the maximal shoulder extension, the serratus anterior contributes to upwardly rotate the scapula. The scapula provides a stable base to transfer forces from the trunk to the shoulder and arm during throwing, and to stabilise the shoulder joint, while creating space in the subacromial area by elevating the acromion when elevating the arm (DiGiovine et al., 1992; Meister, 2000; Mihata et al., 2015). Earlier studies (Kibler et al., 2013; Meister, 2000; Neer, 2005) have described muscle force couples for the scapula, which includes upper and lower parts of the trapezius paired with the serratus anterior muscle. To elevate the acromion, the muscle force couple of the lower trapezius and serratus must be appropriate. The analysis shows a significant interaction in the timing of the upper trapezius before maximal humeral extension, and an increased muscular activity in the serratus anterior after the FFP before the maximal shoulder extension, and this may be a compensation for the stable changes of muscle peak activity in the upper and lower trapezius, change in timing of the upper trapezius, and the increased maximal external shoulder rotation (Figure 6). A decreased elevation of the acromion will decrease the subacromial space and increase the risk of subacromial impingement (Meister, 2000; Neer, 2005). Earlier studies have described that forces generated during the overhead throwing motion create stress across the shoulder joint, and can develop damage in the joint, even though no earlier injury has been registered (Escamilla & Andrews, 2009; Escamilla et al., 2007, 2014; Jobe et al., 1989). Therefore, based on this analysis, the importance of a well-coordinated muscle recruitment of the scapula humeral muscles will impact the kinematics of the overhead throwing motion while playing with or without shoulder pain.