European Journal of Applied Physiology

, Volume 101, Issue 4, pp 445–456 | Cite as

The influence of body posture, arm movement, and work stress on trapezius activity during computer work

  • Paul Jarle Mork
  • Rolf H. WestgaardEmail author
Original Article


The study aimed to determine the influence of arm posture and movement on trapezius activity of computer workers, considering the full workday. A second aim was to investigate if work periods perceived as stressful were associated with elevated or more sustained muscle activity pattern. Twenty-six computer workers performing call-center (n = 11), help desk (n = 7), or secretarial (n = 8) work tasks participated. Bilateral trapezius surface electromyographic (sEMG) activity and heart rate was recorded throughout the workday. Simultaneous inclinometer recordings from left thigh and upper arms identified periods with sitting, standing, and walking, as well as arm posture and movement. Perceived work stress and tension were recorded on visual analog scales (VAS) every hour. Trapezius sEMG activity was low in seated posture [group median 1.8 and 0.9% of activity at maximal voluntary contraction (%EMGmax) for dominant and non-dominant side] and was elevated in standing (3.0 and 2.5% EMGmax) and walking (3.9 and 3.4% EMGmax). In seated posture (mean duration 79% of workday) arm movement consistently influenced trapezius activity, accounting for ∼20% of intra-individual variation in trapezius activity. Arm elevation was on average not associated with trapezius activity when seated; however, considerable individual variation was observed. There was no indication of increase in trapezius activity or more sustained activity pattern, nor in heart rate, in high-stress versus low-stress periods, comparing periods with seated posture for the subjects reporting contrasts of at least two VAS units in stress (n = 16) or tension (n = 14) score.


Electromyography Trapezius Shoulder and neck pain Computer work Posture Work stress 



This study was supported by the Norwegian Research Council.


  1. Blangsted AK, Hansen K, Jensen C (2003) Muscle activity during computer-based office work in relation to self-reported job demands and gender. Eur J Appl Physiol 89:352–358PubMedGoogle Scholar
  2. Blangsted AK, Søgaard K, Christensen H, Sjøgaard G (2004) The effect of physical and psychosocial loads on the trapezius muscle activity during computer keying tasks and rest periods. Eur J Appl Physiol 91:253–258PubMedCrossRefGoogle Scholar
  3. Blatter BM, Bongers PM (2002) Duration of computer use and mouse use in relation to musculoskeletal disorders of neck and upper limb. Int J Ind Ergon 30:295–306CrossRefGoogle Scholar
  4. Byström JU, Hansson G-Å, Rylander L, Ohlsson K, Källrot G, Skerfving S (2002) Physical workload on neck and upper limb using two CAD applications. Appl Ergon 33:63–74PubMedCrossRefGoogle Scholar
  5. Carter JB, Banister EW (1994) Musculoskeletal problems in VDT work: a review. Ergonomics 37:1623–1648PubMedCrossRefGoogle Scholar
  6. Eriksen W (2004) Linking work factors to neck myalgia: the nitric oxide/oxygen ratio hypothesis. Med Hypotheses 62:721–726PubMedCrossRefGoogle Scholar
  7. Ferreira M, de Souza Conceicão GM, Saldiva PHN (1997) Work organization is significantly associated with upper extremities musculoskeletal disorders among employees engaged in interactive computer-telephone tasks of an international bank subsidiary in São Paulo, Brazil. Am J Ind Med 31:468–473CrossRefGoogle Scholar
  8. Galinsky TL, Swanson NG, Sauter SL, Hurrell JJ, Schleifer LM (2000) A field study of supplementary rest breaks for data-entry operators. Ergonomics 43:622–638PubMedCrossRefGoogle Scholar
  9. Hagen KB, Sørhagen O, Harms-Ringdahl K (1995) Influence of weight and frequency on thigh and lower-trunk motion during repetitive lifting employing stoop and squat techniques. Clin Biomech 10:122–127CrossRefGoogle Scholar
  10. Holte KA, Vasseljen O, Westgaard RH (2003) Exploring perceived tension as a response to psychosocial work stress. Scand J Work Environ Health 29:124–133PubMedGoogle Scholar
  11. Holte KA, Westgaard RH (2002a) Further studies of shoulder and neck pain and exposures in customer service work with low biomechanical demands. Ergonomics 45:887–909PubMedCrossRefGoogle Scholar
  12. Holte KA, Westgaard RH (2002b) Daytime trapezius muscle activity and shoulder-neck pain of service workers with work stress and low biomechanical exposure. Am J Ind Med 41:393–405PubMedCrossRefGoogle Scholar
  13. Hubbard DR, Berkoff GM (1993) Myofascial trigger points show spontaneous needle EMG activity. Spine 18:1803–1807PubMedCrossRefGoogle Scholar
  14. Jensen C, Borg V, Finsen L, Hansen K, Juul-Kristensen B (1998) Job demands, muscle activity and musculoskeletal symptoms in relation to work with the computer mouse. Scand J Work Environ Health 24:418–424PubMedGoogle Scholar
  15. Jensen C, Finsen L, Søgaard K, Christensen H (2002) Musculoskeletal symptoms and duration of computer and mouse use. Int J Ind Ergon 30:265–275CrossRefGoogle Scholar
  16. Jensen C, Vasseljen O, Westgaard RH (1993) The influence of electrode position on bipolar surface electromyogram recordings of the upper trapezius muscle. Eur J Appl Physiol 67:266–273CrossRefGoogle Scholar
  17. Jonsson B (1978) Kinesiology. With special reference to electromyographic kinesiology. In: Cobb WA, Van Duijn H (eds) Contemporary clinical neurophysiology (EEG Suppl. No. 34). Elsevier, Amsterdam, pp 417–428Google Scholar
  18. Juul-Kristensen B, Søgaard K, Strøyer J, Jensen C (2004) Computer users’ risk factors for developing shoulder, elbow and back symptoms. Scand J Work Environ Health 30:390–398PubMedGoogle Scholar
  19. Kern DS, Semmler JG, Enoka RM (2001) Long-term activity in upper- and lower-limb muscles of humans. J Appl Physiol 91:2224–2232PubMedGoogle Scholar
  20. Knardahl S (2002) Psychophysiological mechanisms of pain in computer work: the blood vessel-nociceptor interaction hypothesis. Work Stress 16:179–189CrossRefGoogle Scholar
  21. Larsman P, Sandsjö L, Klipstein A, Vollenbroek-Hutten M, Christensen H (2006) Perceived work demands, felt stress, and musculoskeletal neck/shoulder symptoms among elderly female computer users. The NEW study. Eur J Appl Physiol 96:127–135PubMedCrossRefGoogle Scholar
  22. Lundberg U, Forsman M, Zachau G, Eklöf M, Palmerud G, Melin B, Kadefors R (2002) Effects of experimentally induced mental and physical stress on motor unit recruitment in the trapezius muscle. Work Stress 16:166–178CrossRefGoogle Scholar
  23. Marcus M, Gerr F, Monteilh C, Ortiz DJ, Gentry E, Cohen S, Edwards A, Ensor C, Kleinbaum D (2002) A prospective study of computer users: II. Postural risk factors for musculoskeletal symptoms and disorders. Am J Ind Med 41:236–249PubMedCrossRefGoogle Scholar
  24. Mathiassen SE, Winkel J (1990) Electromyographic activity in the shoulder-neck region according to arm position and glenohumeral torque. Eur J Appl Physiol 61:370–379CrossRefGoogle Scholar
  25. McNulty WH, Gevirtz RN, Hubbard DR, Berkoff GM (1994) Needle electromyographic evaluation of trigger point response to a psychological stressor. Psychophysiology 31:313–316PubMedCrossRefGoogle Scholar
  26. Melin B, Lundberg U (1997) A biopsychosocial approach to work-stress and musculoskeletal disorders. J Psychophysiol 11:238–247Google Scholar
  27. Mork PJ, Westgaard RH (2004) The association between nocturnal trapezius muscle activity and shoulder and neck pain. Eur J Appl Physiol 92:18–25PubMedCrossRefGoogle Scholar
  28. Mork PJ, Westgaard RH (2005) Long-term electromyographic activity in upper trapezius and low back muscles of females with moderate physical activity. J Appl Physiol 99:570–578PubMedCrossRefGoogle Scholar
  29. Mork PJ, Westgaard RH (2006) Low-amplitude trapezius activity in work and leisure and the relation to shoulder and neck pain. J Appl Physiol 100:1142–1149PubMedCrossRefGoogle Scholar
  30. Nakazawa T, Okubo Y, Suwazono Y, Kobayashi E, Komine S, Kato N, Nogawa K (2002) Association between duration of daily VDT use and subjective symptoms. Am J Ind Med 42:421–426PubMedCrossRefGoogle Scholar
  31. Nordstrom MA, Miles TS (1991) Instability of motor unit firing rates during prolonged isometric contractions in human masseter. Brain Res 549:268–274PubMedCrossRefGoogle Scholar
  32. Norman K, Nilsson T, Hagberg M, Wigaeus Tornqvist E, Toomingas A (2004) Working conditions and health among female and male employees at a call center in Sweden. Am J Ind Med 46:55–62PubMedCrossRefGoogle Scholar
  33. Romaiguère P, Vedel J-P, Pagni S (1993) Comparison of fluctuations of motor unit recruitment and de-recruitment thresholds in man. Exp Brain Res 95:517–522PubMedCrossRefGoogle Scholar
  34. Saltin B, Gollnick PD (1983) Skeletal muscle adaptability: significance for metabolism and performance. In: Peachey LD, Adrian RH, Geiger SR (eds) Handbook of physiology. American Physiological Society, Bethesda, MD, pp 555–631Google Scholar
  35. Simons DG (2004) Review of enigmatic MTrPs as a common cause of enigmatic musculoskeletal pain and dysfunction. J Electromyogr Kinesiol 14:95–107PubMedCrossRefGoogle Scholar
  36. Sjøgaard G, Lundberg U, Kadefors R (2000) The role of muscle activity and mental load in the development of pain and degenerative processes at the muscle cell level during computer work. Eur J Appl Physiol 83:99–105PubMedCrossRefGoogle Scholar
  37. Thorn S, Forsman M, Zhang Q, Taoda K (2002) Low-threshold motor unit activity during a 1-h static contraction in the trapezius muscle. Int J Ind Ergon 30:225–236CrossRefGoogle Scholar
  38. Vasseljen O, Westgaard RH (1997) Arm and trunk posture during work in relation to shoulder and neck pain and trapezius activity. Clin Biomech 12:22–31CrossRefGoogle Scholar
  39. Veiersted KB, Westgaard RH (1994) Subjectively assessed occupational and individual parameters as risk factors for trapezius myalgia. Int J Ind Ergon 13:235–245CrossRefGoogle Scholar
  40. Veiersted KB, Westgaard RH, Andersen P (1990) Pattern of muscle activity during sterotyped work and its relation to muscle pain. Int Arch Occup Environ Health 62:31–41PubMedCrossRefGoogle Scholar
  41. Wærsted M, Bjørklund RA, Westgaard RH (1994) The effect of motivation on shoulder-muscle tension in attention-demanding tasks. Ergonomics 37:363–376PubMedGoogle Scholar
  42. Wærsted M, Eken T, Westgaard RH (1996) Activity of single motor units in attention-demanding tasks: firing pattern in the human trapezius muscle. Eur J Appl Physiol 72:323–329CrossRefGoogle Scholar
  43. Wahlström J, Hagberg M, Johnson PW, Svensson J, Rempel D (2002) Influence of time pressure and verbal provocation on physiological and psychological reactions during work with a computer mouse. Eur J Appl Physiol 87:257–263PubMedCrossRefGoogle Scholar
  44. Wahlström J, Hagberg M, Toomingas A, Wigaeus Tornqvist E (2004) Perceived muscular tension, job strain, physical exposure, and associations with neck pain among VDU users; a prospective cohort study. Occup Environ Med 61:523–528PubMedCrossRefGoogle Scholar
  45. Westad C, Mork PJ, Westgaard RH (2004) Firing patterns of low-threshold trapezius motor units in feedback-controlled contractions and vocational motor activities. Exp Brain Res 158:465–473PubMedCrossRefGoogle Scholar
  46. Westad C, Westgaard RH, De Luca CJ (2003) Motor unit recruitment and derecruitment induced by brief increase in contraction amplitude of the human trapezius muscle. J Physiol 552:645–656PubMedCrossRefGoogle Scholar
  47. Westad C, Westgaard RH (2005) The influence of contraction amplitude and firing history on spike-triggered averaged trapezius motor unit potentials. J Physiol 562:965–975PubMedCrossRefGoogle Scholar
  48. Westgaard RH, Jansen T (1992) Individual and work related factors associated with symptoms of musculoskeletal complaints. I A quantitative registration system. Br J Ind Med 49:147–153PubMedGoogle Scholar

Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.Department of Industrial Economics and Technology ManagementNorwegian University of Science and TechnologyTrondheimNorway
  2. 2.Human Movement Science Programme, Faculty of Social Sciences and Technology ManagementNorwegian University of Science and TechnologyTrondheimNorway

Personalised recommendations