Pattern of muscle activity during stereotyped work and its relation to muscle pain

  • K. B. Veiersted
  • R. H. Westgaard
  • P. Andersen
Original Articles


Standardized and machine-paced work tasks at a packing machine were examined to evaluate interindividual variability of muscle activity patterns. Ten trained female workers, without musculo-skeletal complaints at the time of the recording, performed the work tasks while electromyographic (EMG) recordings were obtained from both upper trapezius muscles. Static muscle activity and periods of between 0.2 and 2 s duration with low muscle activity, EMG gaps, were analysed. Complaints of muscular fatigue, soreness or pain in the neck and shoulders during the last 12 months were recorded. The level of static muscle activity was 1.6 (range 0.4 to 2.5) per cent of maximal voluntary contraction and median number of EMG gaps was 4.8 (range 0.8 to 20) per minute. Workers with previous episodes of complaints (five subjects) had higher levels of static muscle activity and fewer EMG gaps than workers without such episodes (p < 0.05, Wilcoxon 2-sample test, one-tailed). Considerable interindividual variability of muscle activity patterns was found in spite of stereotyped work. No causal relations may be inferred from the correlation between the level of trapezius activity and complaints, though it indicates that individual, inexpedient muscle activity patterns may constitute an important risk factor for development of musculo-skeletal complaints.

Key words

Interindividual variability Static workload EMG gaps Neck and shoulder complaints Electromyography 


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  1. Aarås A, Westgaard RH (1987) Further studies of postural load and musculo-skeletal injuries of workers at an electromechanical assembly plant. Appl Ergonomics 18:211–219CrossRefGoogle Scholar
  2. Antti CJ (1977) Relationship between time means of external load and EMG amplitude in long term myoelectric studies. Electromyogr Clin Neurophysiol 17:45–53PubMedGoogle Scholar
  3. Bjelle A, Hagberg M, Michaelson G (1981) Occupational and individual factors in acute shoulder-neck disorders among industrial workers. Br J Ind Med 38:356–363PubMedGoogle Scholar
  4. Björkstén M, Jonsson B (1977) Endurance limit of force in long-term intermittent static contractions. Scand J Work Environ Health 3:23–27PubMedGoogle Scholar
  5. Christensen H (1986) Muscle activity and fatigue in the shoulder muscles of assembly-plant employees. Scand J Work Environ Health 12:582–587PubMedGoogle Scholar
  6. Erdelyi A, Sihvonen T, Helin P, Hänninen O (1988) Shoulder strain in keyboard workers and its alleviation by arm supports. Int Arch Occup Environ Health 60:119–124PubMedCrossRefGoogle Scholar
  7. Hagberg M (1984) Occupational musculoskeletal stress and disorders of the neck and shoulder: a review of possible pathophysiology. Int Arch Occup Environ Health 53:269–278PubMedCrossRefGoogle Scholar
  8. Hagberg M, Sundelin G (1986) Discomfort and load on the upper trapezius muscle when operating a wordprocessor. Ergonomics 29:1637–1645PubMedCrossRefGoogle Scholar
  9. Hagberg M, Wegman DH (1987) Prevalence rates and odds ratios of shoulder-neck diseases in different occupational groups. Br J Ind Med 44:602–610PubMedGoogle Scholar
  10. Hennig R, Lømo T (1985) Firing patterns of motor units in normal rats. Nature 314:164–166PubMedCrossRefGoogle Scholar
  11. Hennig R, Lømo T (1987) Gradation of force output in normal fast and slow muscles of the rat. Acta Physiol Scand 130:133–142PubMedCrossRefGoogle Scholar
  12. Jonsson B (1978) Kinesiology — with special reference to electromyographic kinesiology. In: Cobb WA, Van Duijn H (eds) Contemp Clin Neurophysiol 34:417–428. Elsevier Scientific Publishing Company, AmsterdamGoogle Scholar
  13. Jonsson B (1982) Measurement and evaluation of local muscular strain in the shoulder during constrained work. J Hum Ergol 11:73–88CrossRefGoogle Scholar
  14. Kilbom Å, Persson J, Jonsson BG (1986) Disorders of the cervicobrachial region among female workers in the electronics industry. Int J Ind Ergonomics 1:37–47CrossRefGoogle Scholar
  15. Kilbom Å, Persson J (1987) Work technique and its consequences for musculoskeletal disorders. Ergonomics 30:273–279PubMedCrossRefGoogle Scholar
  16. Luopajärvi T, Kuorinka I, Virolainen M, Holmberg M (1979) Prevalence of tenosynovitis and other injuries of the upper extremities in repetitive work. Scand J Work Environ Health [Suppl 3] 6:48–55Google Scholar
  17. Milner-Brown HS, Stein RB, Yemm R (1973) The olderly recruitment of human motor units during voluntary isometric contractions. J Physiol 230:359–370PubMedGoogle Scholar
  18. Nowlin TP, Bailey JO (1985) Evaluation of the effect of anxiety on the masseteric silent period duration. J Oral Rehabil 12:119–122PubMedCrossRefGoogle Scholar
  19. Parenmark G, Engvall B, Malmkvist A-K (1988) Ergonomic on-the-job training of assembly workers. Appl Ergonomics 19:143–146CrossRefGoogle Scholar
  20. Punnett L, Robins JM, Wegman, Keyserling WM (1985) Soft tissue disorders in the upper limbs of female garment workers. Scand J Work Environ Health 11:417–425PubMedGoogle Scholar
  21. Rohmert W (1960) Ermittlung von Erholungspausen für statische Arbeit des Menschen. Int Z Physiol Einschl Arbeitsphysiol 18:123–164Google Scholar
  22. Schüldt K, Ekholm J, Harms-Ringdahl K, Aborelius UP, Nemeth G (1987) Influence of sitting postures on neck and shoulder e.m.g. during arm-hand work movements. Clin Biomech 2:126–139CrossRefGoogle Scholar
  23. Walter CB (1988) The influence of agonist premotor silence and the stretch-shortening cycle on contractile rate in active skeletal muscle. Eur J Appl Physiol 57:577–582CrossRefGoogle Scholar
  24. Westgaard RH (1988) Measurement and evaluation of postural load in occupational work situations. Eur J Appl Physiol 57:291–304CrossRefGoogle Scholar
  25. Westgaard RH, Bjørklund R (1987) Generation of muscle tension additional to postural muscle load. Ergonomics 30:911–923PubMedCrossRefGoogle Scholar
  26. Westgaard RH, Wærsted M, Jansen T, Aarås A (1986) Muscle load and illness associated with constrained body postures. In: Corlett N, Wilson J, Manenica I (eds) The ergonomics of working posture. Taylor & Francis, London, pp 5–18Google Scholar
  27. Winkel J, Bendix T (1984) A method for electromyographic analysis of muscular contraction frequencies. Eur J Appl Physiol 53:112–117CrossRefGoogle Scholar
  28. Zipp P (1982) Recommendations for the standardization of lead positions in surface electromyography. Eur J Appl Physiol 50:41–54CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 1990

Authors and Affiliations

  • K. B. Veiersted
    • 1
  • R. H. Westgaard
    • 2
  • P. Andersen
    • 3
  1. 1.National Institute of Occupational HealthOslo 1Norway
  2. 2.Division of Organization and Work ScienceThe Norwegian Institute of TechnologyTrondheim-NTHNorway
  3. 3.Institute of NeurophysiologyUniversity of OsloOslo 1Norway

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