Sammendrag
LOW-LEVEL MUSCLE ACTIVITY AS A RISK FACTOR FOR WORK RELATED SHOULDER-NECK PAIN: COMPARISON OF TRAPEZIUS AND EXTREMITY MUSCLES DURING WORK AND LEISURE Mork, P.J.M., Holte, K.A., Westgaard, R.H. The Norwegian University of Science and Technology, N-7491 Trondheim, Norway. BACKGROUND AND AIM Work-related musculoskeletal pain is more frequent in the upper (descending) trapezius than in other muscles in occupational settings with low physical workload (1). If muscle activity is a causal factor in pain induction, it can be argued that frequently pain-afflicted muscles should show elevated activity levels, or sustained activity patterns, compared to muscles not frequently associated with pain. In addition, if workload represents a significant risk factor for neck and shoulder pain, it can be hypothesised that the EMG response during work should differ from leisure for the pain-afflicted muscles. The study aims to characterise low-level muscle activity during work and leisure, and to examine potential differences between muscles that are frequently pain-afflicted and muscles that seldom are associated with pain. METHOD Vocational EMG was recorded over the workday and the subsequent leisure period for 27 secretaries. Seven muscle sites were recorded including the upper and lower trapezius (bilaterally), the middle deltoideus, the biceps and the hand flexors. In the analysis, variables quantifying general muscle activation (static, median activity level) were included, as were a variable quantifying the duration of pauses in the EMG activity. RESULTS Trapezius muscles (upper and lower) generated higher EMG levels than the other muscles during work. During leisure, this difference was less profound in that trapezius activity was reduced, while for the other muscles only small differences in activity level were discerned from work to leisure. CONCLUSION If muscle activity is a causal factor in pain induction, the study indicates that the trapezius muscle may be more vulnerable than other muscles to pain development in occupational settings with low physi
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