European Journal of Applied Physiology

, Volume 106, Issue 2, pp 243–251 | Cite as

Examining the low, high and range measures of muscle activity amplitudes in symptomatic and asymptomatic computer users performing typing and mousing tasks

  • Grace P. Y. Szeto
  • Leon M. Straker
  • Peter B. O’Sullivan
Original Article


Past studies on work-related musculoskeletal disorders (WMSD) have reported increased median muscle activities in terms of 50th% of amplitude probability distribution function (APDF), and this was thought to be a manifestation of altered motor control—an important mechanism contributing to WMSD. The present study aimed to examine whether such altered motor control was also present in other parameters of APDF—the 10th and 90th% values, which can be considered indicators of the low and high measures of muscle activity. The difference between 10th and 90th% APDF can be considered an indicator of the variation in muscle activity amplitude (the “APDF range”). Surface electromyography was examined in female office workers as Case (n = 21) and Control (n = 18) subjects. The APDF variables were measured in cervical erector spinae (CES) and upper trapezius (UT) muscles during typing, mousing and type-and-mouse, for 20 min each. The Case Group had significantly higher CES activity in the 10th, 90th% and APDF range compared to Controls. The UT muscles showed similar trends but the between-group differences were not statistically significant. These results have demonstrated the robustness of the APDF variables as sensitive indicators of motor control variations in symptomatic subjects with musculoskeletal disorders.


Computer use EMG Trapezius WMSD Neck pain Motor control 


  1. Aarås A, Veierød MB, Larsen S, Ortengren R, Ro O (1996) Reproducibility and stability of normalized EMG measurements on musculus trapezius. Ergonomics 39(2):171–185Google Scholar
  2. Aarås A, Ro O (1999) Work with visual display unit (VDU). Health consequences. In: Proceedings of 35th Annual conference of the Ergonomics Society of Australia Inc., Fremantle (WA) ESA, pp 33–49Google Scholar
  3. Aarås A, Fostervold KI, Ro O, Thoresen M (1997) Postural load during VDU work: a comparison between various work postures. Ergonomics 40(11):1255–1268PubMedCrossRefGoogle Scholar
  4. Bansevicius D, Westgaard RH, Jensen C (1997) Mental stress of long duration: EMG activity, perceived tension, fatigue, and pain development in pain-free subjects. Headache 37:499–510PubMedCrossRefGoogle Scholar
  5. Blangsted AK, Hansen K, Jensen C (2003) Muscle activity during computer-based office work in relation to self-reported job demands and gender. Euro J Appl Physiol 89(3–4):352–358CrossRefGoogle Scholar
  6. Cram JR, Kasman GS, Holtz J (1998) Introduction to surface electromyography, 1st edn. Aspen Publisher Incorporation, Gaithersburg, pp 15–20Google Scholar
  7. Dennerlein JT, Johnson PW (2006) Different computer tasks affect the exposure of the upper extremity to biomechanical risk factors. Ergonomics 49(1):45–61PubMedCrossRefGoogle Scholar
  8. Falla D, Bilenkij G, Jull G (2004) Patients with chronic neck pain demonstrate altered patterns of muscle activation during performance of a functional upper limb task. Spine 29(13):1436–1440PubMedCrossRefGoogle Scholar
  9. Hägg GM (1991) Static work load and occupational myalgia: a new explanation model. In: Anderson P, Hobart D, Dainoff J (eds) Electromyographical kinesiology. Elsevier, Amsterdam, pp 141–144Google Scholar
  10. Hägg GM, Astrom A (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 69:423–432PubMedCrossRefGoogle Scholar
  11. Hansson GA, Nordander C, Asterland P, Ohlsson K, Stromberg U, Skerfving S, Rempel D (2000) Sensitivity of trapezius electromyography to differences between work tasks—influence of gap definition and normalization methods. J Electromyogr Kinesiol 10:103–115PubMedCrossRefGoogle Scholar
  12. Hermen HJ, Freriks B, Merletti R et al (1999) European recommendations for surface electromyography: results of the SENIAM project, 2nd edn. Roessingh Research and Development, The Netherlands, pp 101–110Google Scholar
  13. Holte KA, Westgaard RH (2002) 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
  14. Jonsson B (1982) Measurement and evaluation of local muscular strain in the shoulder during constrained work. J Hum Ergol 11:73–88CrossRefGoogle Scholar
  15. Jonsson B, Persson J, Kilbom A (1988) Disorders of the cervicobrachial region among female workers in the electronic industry: a two-year follow up. Int J Ind Ergon 3:1–12CrossRefGoogle Scholar
  16. Kleine B-U, Schumann N-P, Bradl I, Grieshaber R, Scholle H-C (1999) Surface EMG of shoulder and back muscles and posture analysis in secretaries typing at visual display units. Int Arch Occup Environ Health 72:387–394PubMedCrossRefGoogle Scholar
  17. Kuorinka I, Jonsson B, Kilbom Å, Vinterberg H, Biering-Sörenson F, Andersson A, Jorgensen K (1987) Standardised Nordic questionnaires for the analysis of musculoskeletal symptoms. Appl Ergon 18(3):233–237PubMedCrossRefGoogle Scholar
  18. Loomis D, Kromhout H (2004) Exposure variability: concepts and applications in occupational epidemiology. Am J Ind Med 45:113–122PubMedCrossRefGoogle Scholar
  19. Madeleine P, Lundager B, Voigt M, Arendt-Nielsen L (1999) Shoulder muscle co-ordination during chronic and acute experimental neck–shoulder pain. Eur J of Appl Physiol 79:127–140CrossRefGoogle Scholar
  20. Madeleine P, Mathiassen SE, Arendt-Nielsen L (2008) Changes in the degree of motor variability associated with experimental and chronic neck–shoulder pain during a standardized repetitive arm movement. Exp Brain Res 185:689–698PubMedCrossRefGoogle Scholar
  21. Mathiassen SE (2006) Diversity and variation in biomechanical exposure: what is it, and why would we like to know? Appl Ergon 37:419–427PubMedCrossRefGoogle Scholar
  22. Mathiassen SE, Winkel J (1991) Quantifying variation in physical load using exposure-vs-time data. Ergonomics 34:1455–1468PubMedCrossRefGoogle Scholar
  23. Mathiassen SE, Moller T, Forsman M (2003) Variability in mechanical exposure within and between individuals performing a highly constrained industrial work. Ergonomics 46:800–824PubMedCrossRefGoogle Scholar
  24. Nederhand MJ, Hermens HJ, Ijzerman MI, Turk DC, Zilvold G (2003) Chronic neck pain disability due to an acute whiplash injury. Pain 102:63–71PubMedCrossRefGoogle Scholar
  25. Nordander C, Hansson GA, Rylander L, Asterland P, Bystrom JU, Ohlsson K et al (2000) Muscular rest and gap frequency as EMG measures of physical exposure: the impact of work tasks and individual related factors. Ergonomics 43(11):1904–1919PubMedCrossRefGoogle Scholar
  26. Roe C, Bjorklund RA, Knardahl S, Waersted M, Vollestad NK (2001) Cognitive performance and muscle activation in workers with chronic shoulder myalgia. Ergonomics 44(1):1–16PubMedCrossRefGoogle Scholar
  27. Sandsjo L, Melin B, Rissen D, Dohns L, Lundberg U (2000) Trapezius muscle activity, neck and shoulder pain, and subjective experiences during monotonous work in women. Eur J Appl Physiol 83:235–238PubMedCrossRefGoogle Scholar
  28. Szeto GPY, Straker LM, O’Sullivan PB (2005a) A comparison of symptomatic and asymptomatic office workers performing monotonous keyboard work-1. Neck and shoulder muscle recruitment patterns. Man Ther 10:270–280PubMedCrossRefGoogle Scholar
  29. Szeto GPY, Straker LM, O’Sullivan PB (2005b) A comparison of symptomatic and asymptomatic office workers performing monotonous keyboard work-2. Neck and shoulder kinematics. Man Ther 10:281–291PubMedCrossRefGoogle Scholar
  30. Szeto GPY, Straker LM, O’Sullivan PB (2005c) The effects of speed and force of keyboard operation on neck–shoulder muscle activities in symptomatic and asymptomatic office workers. Int J Ind Ergon 35:429–444CrossRefGoogle Scholar
  31. Szeto GPY, Straker LM, O’Sullivan PB (2005d) The effects of typing speed and force on motor control in symptomatic and asymptomatic office workers. Int J of Ind Ergon 35:779–795CrossRefGoogle Scholar
  32. Szeto GPY, Straker LM, O’Sullivan PB (2005e) EMG median frequency changes in the neck–shoulder stabilizers of symptomatic office workers when challenged by different physical stressors. J Electromyogr Kinesiol 15:544–555PubMedCrossRefGoogle Scholar
  33. Thorn S, Sogaard K, Kallenberg LAC, Sandsjo L, Sjogaard G, Hermens HJ, Forsman M (2007) Trapezius muscle rest time during standardised computer work—a comparison of female computer users with and without self-reported neck/shoulder complaints. J Electromyogr Kinesiol 17(4):420–427PubMedCrossRefGoogle Scholar
  34. Vasseljen O Jr, Westgaard RH (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 67:11–18PubMedCrossRefGoogle Scholar
  35. Veiersted KB, Westgaard RH, Andersen P (1990) Pattern of muscle activity during stereotyped work and its relation to muscle pain. Int Arch Occup Environ Health 62:31–41PubMedCrossRefGoogle Scholar
  36. Veiersted KB, Westgaard RH, Andersen P (1993) Electromyographic evaluation of muscular work pattern as a predictor of trapezius myalgia. Scand J Work Environ Health 19:284–290PubMedGoogle Scholar
  37. Westgaard RH, Vasseljen O, Holte KA (2001) Trapezius muscle activity as a risk indicator for shoulder and neck pain in female service workers with low biomechanical exposure. Ergonomics 44(3):339–353PubMedCrossRefGoogle Scholar
  38. Zannaro D, Laubli T, Krebs D, Klipstein A, Krueger H (2003) Continuous, intermittent and sporadic motor unit activity in the trapezius muscle during prolonged computer work. J Electromyogr Kinesiol 13:113–124CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Grace P. Y. Szeto
    • 1
  • Leon M. Straker
    • 2
  • Peter B. O’Sullivan
    • 2
  1. 1.Department of Rehabilitation SciencesThe Hong Kong Polytechnic UniversityHung HomHong Kong
  2. 2.School of PhysiotherapyCurtin University of TechnologyPerthAustralia

Personalised recommendations