Surface EMG of shoulder and back muscles and posture analysis in secretaries typing at visual display units

• Published in: International archives of occupational and environmental health Vol. 72; no. 6; pp. 387 - 394
• Main Authors: KLEINE, B.-U, SCHUMANN, N.-P, BRADL, I, GRIESHABER, R, SCHOLLE, H.-C
• Format: Journal Article
• Language: English
• Published: Berlin Springer 08-09-1999
• Subjects: Adult; Analysis of Variance; Back; Biological and medical sciences; Computer Terminals; Electromyography; Female; Humans; Injuries of the limb. Injuries of the spine; Linear Models; Medical sciences; Muscle, Skeletal - physiology; Musculoskeletal Diseases - physiopathology; musculoskeletal system; Occupational Diseases - physiopathology; Posture; Shoulder; Time Factors; Traumas. Diseases due to physical agents; video display terminals; Human; Trapezius muscle; Back (anatomy); Shoulder; Diseases of the osteoarticular system; Computer; Fatigue; Electromyography; Occupational exposure; Display screen; Occupational medicine; Posture
• ISSN: 0340-0131; 1432-1246
• DOI: 10.1007/s004200050390

A study was carried out to investigate temporal changes of activation of shoulder and back muscles in workers at visual display units by means of surface EMG. Moreover, postural parameters were recorded to distinguish fatigue-related from posture-related changes of the myoelectrical activity.
Nine healthy female office workers typed texts spoken from tape during three 1-h-long sessions. After the first and again after the second hour there was a break of 15 min. Sixteen-channel surface EMG was bipolarly recorded from the erector spinae, trapezius, deltoid and sternocleidomastoid muscles. Root mean square (RMS) and power spectrum median frequency of the EMG were calculated. Sitting posture was assessed using an eight-channel movement analysis system with ultrasound markers. The position of the seventh cervical spinous process and the left and the right acromion were analysed synchronously with the EMG characteristics using regression analysis.
The normalised RMS of the left and right trapezius muscle increased, while the median frequency did not change. The increase of the normalised RMS was significantly lower when the linear influence of posture was excluded. On average, the distance between C7 and the left and right acromion decreased within each working an hour. C7 became lower on average by 5.5 mm within an hour, whereas the acromions became lower by only 1.7 mm (left) and 3.3 mm (right).
The increase in trapezius muscle activity was partly related to a lifting of the shoulders to compensate a slight slumping of the back. Another part of the EMG activity increase has to be attributed to fatigue, to attention-related activity or to the combination of both. Therefore, training of the back muscles and a varied organisation of work might have a preventive effect with respect to musculoskeletal complaints in VDU workers.