title: The effect of work-related sustained trapezius muscle activity on the development of neck and shoulder pain among young adults.
abstract: OBJECTIVE
  This study aimed to evaluate if sustained trapezius muscle activity predicts neck and shoulder pain over a 2.5-year period.
  
  
  METHODS
  Forty young adults (15 hairdressers, 14 electricians, 5 students and 6 with various work) were followed during their first years of working life. Self-reported neck and shoulder pain during the last four weeks was assessed seven times over the observational period. Upper-trapezius muscle activity was measured during a full working day by bilateral surface electromyography (EMG) at baseline (winter 2006/7). Sustained trapezius muscle activity was defined as continuous muscle activity with amplitude >0.5% EMGmax lasting >4 minutes. The relative time of sustained muscle activity during the working day was calculated and further classified into low (0-29%), moderate (30-49%) and high (50-100%) level groups.
  
  
  RESULTS
  Generalized estimating equations (GEE), adjusted for time, gender, mechanical workload, control-over-work intensity, physical activity, tobacco use, and prior neck and shoulder pain, showed that participants with a high level of sustained muscle activity had a rate of neck and shoulder pain three times higher than the low level group during a 2.5-year period. The association was strongest at the same time and shortly after the EMG measurement, indicating a time-lag of ≤6 months.
  
  
  CONCLUSIONS
  The results support the hypothesis that sustained trapezius muscle activity is associated with neck and shoulder pain. This association was strongest analyzing cross-sectional and short-term effects.
authors.affiliation: National Institute of Occupational Health, PO Box 8149 Dep, 0033 Oslo, Norway. tno@stami.no
authors.forename: Therese N
authors.initials: TN
authors.lastname: Hanvold
authors.forename: Morten
authors.initials: M
authors.lastname: Wærsted
authors.forename: Anne Marit
authors.initials: AM
authors.lastname: Mengshoel
authors.forename: Espen
authors.initials: E
authors.lastname: Bjertness
authors.forename: Hein
authors.initials: H
authors.lastname: Stigum
authors.forename: Jos
authors.initials: J
authors.lastname: Twisk
authors.forename: Kaj Bo
authors.initials: KB
authors.lastname: Veiersted
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D019547:Neck Pain / Q000503:physiopathology*; D009784:Occupational Diseases; D011446:Prospective Studies; D020069:Shoulder Pain / Q000503:physiopathology*; D064171:Superficial Back Muscles / Q000503:physiopathology*; D055815:Young Adult