Shoulder strain in keyboard workers and its alleviation by arm supports

Abstract

Keyboard work consists mostly of dynamic contractions of the small muscles of the forearms and hands. This is accompanied by continuous activity in the arm, shoulder and neck muscles keeping the head and hand in the correct position. Eliminating the weight from the arm by means of support and the position of the arms influences the electrical activity of shoulder muscles when working at a keyboard. We studied the influence of elbow angle; as well as that of different arm supports, on electrical activity of upper trapezius muscle during keyboard work in healthy workers and persons suffering from shoulder pains. The measurements were carried out in the laboratory. EMG activities, which where measured as mean square root (RMS)-values at every 100-millisecond period in trapezius muscle when working, were lower, the greater the elbow angle. Furthermore electrical activity decreased when subjects used arm supports while working. It is evident that the static load to shoulder muscles can be lowered significantly in keyboard work, when the forearms are at an angle of at least 100 degrees and by using arm supports. The most convienient and ergonomic working position can also be found individually be the method used here.

The impact of computer display height and desk design on muscle activity during information technology work by young adults

“…Aaras et al (1998) and Visser et al (2000) report decreased UT activity with the provision of forearm support. However, Cook et al (2004a,b), Erdelyi et al (1988) and Tepper et al (2003) found no difference in UT activity with forearm support. Differences in the nature of the supports and the nature of the tasks performed may have contributed to the differing results.…”

Electromyographic evaluation of muscular work pattern as a predictor of trapezius myalgia.

“…Crosssectional studies have shown that pat ients with trapezius myalgia use their muscles at a higher static level than healthy subj ec ts do (3)(4)(5). Subjects who ha ve suffered mu scle pain on a previou s occasion, but not during a recording sess ion, have also shown a higher static electromyographic (EMG) level than subj ec ts without sy mptoms (6) .…”

Effects of spinal mobilisations on lumbar and hamstring ROM and sEMG: A randomised control trial

“…Recording MVC would have increased muscle activity potentially influencing data recorded at rest, during ALF and AKE [48] . Within a data collection session where no individual changes to the configuration of the EMG set-up (electrode placement, amplification, filtering) has taken place and whilst under constant temperature and humidity conditions EMG data does not need to be normalised against a MVC to be interpreted [49][50] .…”