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Workspace Design
Published in Stephen Pheasant, Christine M. Haslegrave, Bodyspace, 2018
Stephen Pheasant, Christine M. Haslegrave
The height above the ground at which manual activities are performed by the standing person is a major determinant of that person’s posture. If the working level is too high, the shoulders and upper limbs will be raised, leading to fatigue and strain in the muscles of the shoulder region (trapezius, deltoid, levator scapulae, etc.). If any downward force is required in the task, the upper limbs will be in a position of poor mechanical advantage for providing it. This problem may be avoided if the working level is lower. One commonly hears people talk of ‘using their weight’ or ‘getting their weight on top of the action’. This is probably a misconception: what we really mean is that a vertical force may be exerted with minimal loading to the elbow and shoulder extensor muscles. A downward force, however exerted, can never exceed body weight (unless your feet are bolted to the floor), but in some positions the muscles of your arm may lack the strength to lift your feet off the ground.
Response to High-Frequency Current Passing Through the Body
Published in Leslie A. Geddes, Handbook of Electrical Hazards and Accidents, 1995
Subsequent to the operation, the patient complained of pain in the neck, left arm and shoulder. When seen in the physician’s office three days later, he was unable to completely abduct his left arm. An electromyographic study 18 days after surgery revealed “moderately severe denervation of the rhomboids, levator scapulae, supra-spinatus, infra-spinatus, and trapezius muscles,” prompting the neurologist to note that the results “may provide evidence of involvement of the nerve to the trapezius, dorsal scapular nerve, and supra-scapular nerve. This may be secondary to partial injury to the upper brachial plexus on the left.
Prevalence of scapular dyskinesis in office workers with neck and scapular pain
Published in International Journal of Occupational Safety and Ergonomics, 2023
Mantana Vongsirinavarat, Sukhon Wangbunkhong, Prasert Sakulsriprasert, Haruthai Petviset
SD was hypothesized to affect cervical function by inducing disturbances of the scapular muscles. The load on the cervical spine is predisposed by the altered movements and flexibility of the muscles attached to the cervical spine, specifically the hyperactivity of the upper trapezius (UT) and levator scapulae (LS) muscles. This loading continues to increase the mechanical loading in the cervical spine, causing neck pain [6,15]. These inflexible muscles are also reported to be associated with altered posture and SD. Tightness in the pectoralis minor (PM) and short head of the biceps muscles could result in increased scapular anterior tilt and protraction from increased pulling forces on the coracoid process [16,17]. Individuals with shorter lengths of the PM and UT muscles were found to have a greater risk of SD [16]. Moreover, the alterations of activation and strength of the serratus anterior (SA), middle trapezius (MT) and lower trapezius (LT) muscles could affect the loads and movements of other muscles [18].
Muscle co-contraction in an upper limb musculoskeletal model: EMG-assisted vs. standard load-sharing
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2021
Ehsan Sarshari, Matteo Mancuso, Alexandre Terrier, Alain Farron, Philippe Mullhaupt, Dominique Pioletti
The origins/insertions, via points, and wrapping objects of 42 muscles spanning the upper extremity joints were defined from the MRI scans, including subclavius, serratus anterior upper/middle/lower, trapezius C1-C6/C7/T1/T2-T7, levator scapulae, rhomboid minor/major T1-T2/major T3-T4, pectoralis minor/major clavicular/major sternal/major ribs, latisimuss dorsi thoracic/lumbar/Iliac, deltoid clavicular/acromial/scapular, supraspinatus, infraspinatus, subscapularis, teres minor/major, coracobrachialis, triceps brachii long/medial/lateral, biceps brachii short/long, brachialis, brachioradialis, supinator, pronator Teres, flexor carpi radialis/ulnaris, and extensor carpi radiali long/radialis bervis/ulnaris (Ingram 2015). Each muscle group of the model can be represented by up to 20 strings (Figure 3). Three strings per muscle were considered for the simulations of this study.
Improving Sitting Postures: A Pilot Intervention Using a Wearable Posture Support System
Published in IISE Transactions on Occupational Ergonomics and Human Factors, 2020
In this study, we tested the effects of a posture support system on muscle loads (fatigue) and spine curvature (GWL). In general, using the PSS for six weeks had varying degrees of impact on the dependent measures obtained. Following PSS use, most of the tested muscles exhibited smaller signs of fatigue (i.e., less negative slopes of muscle EMG MPF) during a one-hour seated task. In particular, the left upper trapezius, bilateral levator scapulae, bilateral erector spinae, and bilateral upper paraspinal each had significantly less fatigue after PSS use. These results suggest that the major impacts of the PSS system were in the upper shoulder and upper/middle back areas. Seghers, Jochem, and Spaepen (2003) found that after more than 45 min of continuous sitting, muscles around the neck-shoulder region (e.g., deltoid muscle, trapezius pars descendens, splenius capital) occasionally showed a shift of the EMG power spectrum to lower frequencies. Cervical extensors also show signs of fatigue after 20 minutes of sustained seated postures (McLean, Scott, & Rickards, 1997). Wearing the PSS may have reduced the posture load on those muscles, and thereby have resulted in slower fatigue development around the upper torso. Other muscles, such as the left levator scapulae (LLS), were found to have a slight positive slope with an increased median frequency after using the PSS. Such changes may also indicate that a different muscle recruitment strategy was employed after PSS use.