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Musculoskeletal disorders in the neck, shoulder, and arm are common in some occupational groups, and have been ascribed to high precision demands and sustained static load in the neck-shoulder region. In order to evaluate the influence of precision and force demands in manual work related to arm support, instrument grip size, the muscular activity in neck, shoulder, and arm muscles was recorded by electromyography. This EMG and perceived exertion were estimated during a simulated work situation where 12 subjects followed a rotating track, using a handheld dental instrument. Normalized mean EMG amplitude levels (% reference maximal contraction) were calculated. The analysis of variance of the results showed that (a) the precision factor affected significantly the muscular load of the two dominant muscles with postural stabilization function (extensor carpi radialis and infraspinatus); (b) the force factor itself had no specific influence on the muscular load of the investigated muscles; (c) arm support, but not hand support, was of significant importance for the load of three dominant shoulder muscles (trapezius, supraspinatus, and anterior deltoid); and (d) the two different hand grip diameters did not change the activity of any muscle investigated., NR 20140805

Musculoskeletal disorders are common among dentists, and have been ascribed to the demands of high precision work and sustained static loading in the neck-shoulder region, combined with a flexed and rotated cervical spine. In order to determine muscular load levels during dentistry, activity in neck, shoulder, and arm muscles was recorded using an electromyography technique (EMG). Normalized mean, median, 10th and 90th percentile EMG amplitude levels (% maximal reference contraction, %max-RVC) were calculated during ordinary dental work. Among the muscles investigated, the trapezius muscle on both sides had the highest mean (the right trapezius 9.0% and the left 7.6% of max-RVC) and 10th percentile amplitude levels (both about 2% of max-RVC). The trapezius muscles showed similar myoelectric activity on the right and left side, probably because of similar muscular static load on the both sides. The right extensor carpi radialis muscle had a significantly higher muscular load level than the left one, possibly due to stabilization demands on the dominant wrist during demanding precision work. The infraspinatus muscle had low activity level on both sides, reflecting that the dentists worked with a small degree of arm elevation and external rotation. The dentistry work thus seems to generate relatively high muscular load on both trapezius and dominant extensor-carpi-radialis, and relatively low load on the infraspinatus muscle., NR 20140805