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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.”
Designing for Upper Torso and Arm Anatomy
Published in Karen L. LaBat, Karen S. Ryan, Human Body, 2019
The glenohumeral joint forms the roof of the axilla and the pectoralis major and latissimus dorsi muscles form the bulk of the front and back walls. Serratus anterior, the deep torso muscle which helps to move the scapula on the rib cage, forms the medial wall and the humerus forms the lateral wall. Nerves, arteries and veins, and lymphatic vessels lying between the glenohumeral joint and the more superficial tissues (fascia and skin), pass through the axilla to and from the arm. The skin in the axilla has hair and numerous sweat glands.
Increasing physical activity in the vehicle with an interactive seating system in a male sample
Published in Ergonomics, 2023
Forward head posture is listed as a contributing factor for neck pain in driving, which is further aggravated by sitting with slumped posture. This phenomenon is also referred to as the upper crossed syndrome (Caneiro et al. 2010; Kang et al. 2012). According to Page (2011) the upper crossed syndrome is associated with an hyperactivity of the m. trapezius pars descendens, m. levator scapulae, and the pectoralis muscles as well as an underactivity of the deep cervical flexors, the m. trapezius pars transversa, m. trapezius pars ascendens, and m. serratus anterior. Besides stretching exercises for the rhomboid muscles and the m. trapezius pars descendens, strengthening of the m. trapezius pars transversa and m. trapezius pars ascendens is proposed as a countermeasure by Bae et al. (2016).
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.