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Musculoskeletal system
Published in A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha, Clark’s Procedures in Diagnostic Imaging: A System-Based Approach, 2020
A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha
The shoulder joint is a synovial ball-and-socket joint formed between the head of the humerus and the glenoid cavity of the scapula (Fig. 3.18a). The glenoid cavity is shallow, which makes the joint unstable. It has a wide range of movements and relies on muscle support for stability. The joint capsule is lax to permit the wide range of movements available at the joint. It attaches close to the margin of the head of humerus, except inferiorly where it attaches 2–3 cm distally. The capsule is strengthened by four muscles, subscapularis, supraspinatus, infraspinatus and teres minor, which are known collectively as the rotator cuff. Subscapularis originates on the anterior aspect of the scapula and inserts into the lesser tuberosity of the humerus. Supraspinatus originates from the supraspinous fossa of the scapula and inserts into the superior aspect of the greater tuberosity of the humerus. Infraspinatus originates from the infraspinous fossa on the scapula and inserts into the middle portion of the greater tuberosity. Teres minor originates from the upper two-thirds of the axillary border of the scapula (posterior surface) and inserts into the inferior aspect of the greater tuberosity.
Shoulder problems
Published in Richard Graveling, Ergonomics and Musculoskeletal Disorders (MSDs) in the Workplace, 2018
The supraspinatus muscle runs from the supraspinatus fossa of the scapula (shoulder blade), across the shoulder joint, and attaches to the greater tubercle of the humerus (the bone of the upper arm). It passes over the head of the humerus and underneath the acromial arch of the scapula, a route that makes it particularly susceptible to impingement between these bones. It contributes to abduction of the humerus (moving it sideways, away from the body) and stabilisation of the shoulder joint.
Upper extremity injuries
Published in Youlian Hong, Roger Bartlett, Routledge Handbook of Biomechanics and Human Movement Science, 2008
Ronald F. Zernicke, William C. Whiting, Sarah L. Manske
The supraspinatus tendon is the most commonly injured tendon in the rotator cuff (Li et al., 1999; Figure 28.1). It was previously believed that the high prevalence of tendinopathies in the supraspinatus tendon is due to a hypovascular region found in the distal 1.0–1.5 cm of the tendon (Moseley and Goldie, 1963). More recently, however, researchers found that the vascular pattern may be sufficient to meet the metabolic needs of the muscle (Malcarney and Murrell, 2003).
A design tool to estimate maximum acceptable manual arm forces for above-shoulder work
Published in Ergonomics, 2022
Supraspinatus tendon compression, shear, and tension can also increase when the deltoid muscle, which is the primary muscle for abducting and flexing the shoulder, becomes fatigued. The supraspinatus muscle stabilises the shoulder and assists in abduction when the deltoid is fatigued. For above-shoulder work, once the deltoid fatigues, and the force it can generate is reduced, workers will shift to a shrug posture to reduce loads on the shoulder muscles (Fuller et al. 2009). With deltoid muscle fatigue, the humerus is translated in the superior direction and this increases supraspinatus compression (Dickerson, McDonald, and Chopp-Hurley 2020). Shoulder fatigue may also lead to less scapular rotation during upper arm rotation, and this may further increase impingement (McQuade, Dawson, and Smidt 1998, McQuade, Wei, and Smidt 1995). Muscle fatigue is related to the level of muscle load relative to strength (e.g. Maximum Voluntary Contraction, MVC%) and the duration of muscle load (e.g. duty cycle). Fatigue can be controlled by following recommendations from the Maximum Acceptable Effort (MAE) equation (Potvin 2012) or the ACGIH Upper Limb Localized Fatigue Threshold Limit Value (ACGIH 2016). Repetitive, hand intensive work should be designed so that these guidelines are not exceeded.
Considerations for Industrial Use: A Systematic Review of the Impact of Active and Passive Upper Limb Exoskeletons on Physical Exposures
Published in IISE Transactions on Occupational Ergonomics and Human Factors, 2019
Tasha McFarland, Steven Fischer
While the arm is raised, the subacromial space narrows, and as the muscles of the shoulder fatigue, their ability to maintain the position of the humeral head in the glenohumeral cavity lessens, thereby further reducing the subacromial space (Chen, Simonian, Wickiewicz, Otis, & Warren, 1999; Grieve & Dickerson, 2008). This may increase the risk of tearing or impingement of the supraspinatus tendon and lead to shoulder injury (Grieve & Dickerson, 2008). A study on the effects of shoulder muscle fatigue showed that there were changes in scapulothoracic and glenohumeral motion following a fatigue protocol, in which the most fatigue occurred in the infraspinatus and deltoid muscles (Ebaugh, McClure, & Karduna, 2006). These effects are important within the context of this review, as few studies looked at muscles of the rotator cuff; only one study measured muscular activity of the infraspinatus (IF; Kim & Nussbaum, 2019). Consequently, there was insufficient evidence in the overall literature to determine if passive upper limb exoskeletons can reduce muscular fatigue of the IF muscle. Subsequent studies should monitor the effects on rotator cuff muscles in particular, due to their strong association with shoulder pathology.
Muscle fatigue during assisted violin performance
Published in Ergonomics, 2023
Clara Ziane, Etienne Goubault, Benjamin Michaud, Mickaël Begon, Fabien Dal Maso
Very few studies have assessed MMF during violin playing and never with DAS. Chan et al. (2000) assessed median frequency of left trapezius and found no significant difference before and after a violin practice session of 2–3 hours. Violinists’ RPE had however only reached 3 ± 2 on the CR10 Borg scale (i.e. light perceived exertion). As perceived exertion is not a direct measure of muscle fatigue, it is possible that increases in RPE at low levels of perceived exertion reflect central or neuromuscular junction fatigue (Merletti and Farina 2006) rather than muscle fatigue itself, which makes Chan et al. (2000)’s results difficult to compare with ours. More recently, Moller et al. (2018) showed an EMG shift towards lower frequencies for the left medial deltoid and upper trapezius after one hour of playing the violin in a group of musicians unaffected by PRMD. Consistent with their results, we found a significant decrease in the left medial deltoid’s median frequency during the unassisted condition, while DAS prevented the MMF at the superior trapezius. Trapezius muscles stabilise and support scapular movements. Fatigue at the trapezius can lead to a muscular imbalance and in turn to an upper crossed syndrome, which is one type of the PRMD reported in violinists (Mizrahi 2020). In addition, we observed a beneficial effect of DAS on left supraspinatus’ median frequency. This Condition*Time interaction was only marginally significant (P=0.057) due to small sample size (n = 6) but effect size was large (dz = 1.0), suggesting a true effect of DAS on this muscle’s MMF. The supraspinatus abducts the arm and stabilises the glenohumeral joint. Reduced muscle fatigue of the supraspinatus may limit occurrence of subacromial impingement syndromes, which also are a type of PRMD reported in violinists (Mizrahi 2020). Lower MMF at shoulder muscles were previously reported by a different research team using the same assistive device (Lavallée-Bourget et al. 2022). These latter findings further support DAS benefits, which were observed for relatively short playing times (∼10 minutes) in our study, making passive assistive devices a promising tool to prevent injuries of the left shoulder.