Injury models for musculoskeletal disorders are considered. It is suggested that several injury mechanisms may coexist in the same body region. This has implications for data reduction procedures used in risk evaluation by surface EMG (SEMG). Biomechanical exposure as an injury risk may conceptually be characterized by the three exposure dimensions: amplitude, duration and repetitiveness. The time dimension has become increasingly important since many work tasks are performed at low exposure amplitude. For practical purposes, static activity levels higher than 2% EMGmax appear to signify increased risk of musculoskeletal disorders. However, a lower activity level does not guarantee good health, as risk factors apparently unrelated to muscle activity also exist. Mental stress may be one such risk factor.
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References
1.
HäggG. M. (1991). Static work loads and occupational myalgia - a new explanation model. In AndersonP. A.HobartD. J.DanoffJ. V., Electromyographical Kinesiology (pp. 141–143). Amsterdam: Elsevier.
2.
HäggG. M.ÅströmA. (1997). Load pattern and pressure pain threshold in the upper trapezius muscle and psychosocial factors in medical secretaries with and without shoulder/neck disorders. Int. Arch. Occup. Environ. Health, 69, 423–432.
3.
JensenC.NilsenK.HansenK.WestgaardR. H. (1993). Trapezius muscle load as a risk indicator for occupational shoulder-neck complaints. Int. Arch. Occup. Environ. Health, 64, 415–423,.
4.
JonssonB. (1978). Kinesiology - with special reference to electromyographic kinesiology. In CobbW. A.Van DuijnH.Contemporary clinical neurophysiology. EEG (Suppl. No. 34) (pp. 417–428). Amsterdam: Elsevier.
5.
JonssonB. (1982). Measurement and evaluation of local muscular strain in the shoulder during constrained work. J. Human Ergol., 11, 73–88.
6.
MathiassenS. E.WinkelJ. (1991). Quantifying variation in physical load using exposure-vs-time data. Ergonomics, 34, 1455–1468.
7.
MonodH. (1956). Contributions á l'étude du travail statique. Paris: Institut National de Securité.
8.
RohmertW. (1960). Ermittlung von Erholungspausen für statische Arbeit des Menschen. Int. Z. angew. Physiol. einschl. Arbeitsphysiol., 18, 123–164.
9.
RoyS. H.BonatoP.KnaflitzM. (1998). EMG assessment of back muscle function during cyclical lifting. J. Electromyograph. Kinesiol., 8, 233–245.
10.
RoyS. H.OddsonL. I. E. (1998). Classification of paraspinal muscle impairments by surface electromyography. Phys. Ther., 78, 838–851.
11.
VasseljenO.WestgaardR. H. (1995). A case-control study of trapezius muscle activity in office and manual workers with shoulder and neck pain and symptom-free controls. Int. Arch. Occup. Environ. Health, 67, 11–18.
12.
VeierstedK. B.WestgaardR. H.AndersenP. (1990). Patterns of muscle activity during stereotyped work and its relation to muscle pain. Int. Arch. Occup. Environ. Health, 62, 31–41.
13.
VeierstedK. B.WestgaardR. H.AndersenP. (1993). Electromyographic evaluation of muscular work pattern as a predictor of trapezius myalgia. Scand. J. Work. Environ. Health, 19, 284–290.
14.
WestgaardR. H. (1999). Effects of physical and mental stressors on muscle pain. Scand. J. Work Environ. Health, 25 (suppl.4), 19–24.
15.
WestgaardR. H.BjørklundR. (1987). Generation of muscle tension additional to postural muscle load. Ergonomics, 30, 911–923.
16.
WestgaardR. H.De LucaC. J. (1999). Motor unit substitution in long-duration contractions of the human trapezius muscle. J. Neurophysiol., 82, 501–504.
17.
WestgaardR. H.JansenT.JensenC. (1996). EMG of neck and shoulder muscles: The relationship between muscle activity and muscle pain in occupational settings. In KumarS.MitalA.Electromyography in Ergonomics (pp. 227–258). London: Taylor & Francis.
18.
WestgaardR. H.WinkelJ. (1996). Guidelines for occupational musculoskeletal load as a basis for intervention: A critical review. Appl. Ergon., 27, 79–88.
19.
WinkelJ.WestgaardR. H. (1992). Occupational and individual risk factors for shoulder-neck complaints: Part II - The scientific basis (literature review) for the guide. Int. J. Ind. Erg., 10, 85–104.
20.
WærstedM.BjørklundR. A.WestgaardR. H. (1994). The effect of motivation on shoulder-muscle tension in attention-demanding tasks. Ergonomics, 37, 363–376.
