EFFECTS OF PRECISION AND FORCE DEMANDS, GRIP DIAMETER, AND ARM SUPPORT DURING MANUAL WORK - AN ELECTROMYOGRAPHIC STUDY

Musculoskeletal disorders in the neck, shoulder, and arm are common in some occupational groups, and have been ascribed to high precision de mands and sustained static load in the neck-shoulder region. In order to evaluate the influence of precision and force demands in manual wor k related to arm support, instrument grip size, the muscular activity in neck, shoulder, and arm muscles was recorded by electromyography. T his EMG and perceived exertion were estimated during a simulated work situation where 12 subjects followed a rotating track, using a handhel d 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 t he muscular load of the two dominant muscles with postural stabilizati on function (extensor carpi radialis and infraspinatus); (b) the force factor itself had no specific influence on the muscular load of the i nvestigated muscles; (c) arm support, but not hand support, was of sig nificant importance for the load of three dominant shoulder muscles (t rapezius, supraspinatus, and anterior deltoid); and (d) the two differ ent hand grip diameters did not change the activity of any muscle inve stigated.