title: Chronic pain and difficulty in relaxing postural muscles in patients with fibromyalgia and chronic whiplash associated disorders.
abstract: OBJECTIVE
  To investigate if muscle tension according to the surface electromyogram (EMG) of the shoulder flexors is increased in consecutive patients with fibromyalgia (FM) or chronic whiplash associated disorders (WAD).
  
  
  METHODS
  A total of 59 consecutive patients with FM (n = 36) or chronic WAD (n = 23) performed 100 maximal isokinetic contractions combined with surface electromyography of the trapezius and infraspinatus. A randomized group of pain-free female (n = 27) subjects served as control group. Peak torque initially (Pti) and absolute and relative peak torque at endurance level (PTe, PTer) were registered as output variables, together with the EMG level of unnecessary muscle tension, i.e., the signal amplitude ratio (SAR).
  
  
  RESULTS
  The patient groups had a higher level of unnecessary tension initially and at the endurance level. The patients had lower absolute output (PTi and PTe), but the relative levels (PTer) did not differ comparing all 3 groups. Subjects with FM had significantly higher body mass index (BMI) than the other groups. BMI did not influence the SAR but correlated positively with PTi.
  
  
  CONCLUSIONS
  The results confirmed earlier findings that groups of patients with chronic pain have increased muscle tension and decreased output during dynamic activity compared to pain-free controls. However, the results indicated there is heterogeneity within groups of patients with the same chronic pain disorder and that not all patients with chronic pain have increased muscle tension.
authors.affiliation: Department of Rehabilitation Medicine, INR, Faculty of Health Sciences, Pain and Rehabilitation Centre, University Hospital, Linköping, Sweden.
authors.forename: J
authors.initials: J
authors.lastname: Elert
authors.forename: S A
authors.initials: SA
authors.lastname: Kendall
authors.forename: B
authors.initials: B
authors.lastname: Larsson
authors.forename: B
authors.initials: B
authors.lastname: Månsson
authors.forename: B
authors.initials: B
authors.lastname: Gerdle
mesh_terms: D000328:Adult; D002908:Chronic Disease; D004576:Electromyography; D005260:Female; D005356:Fibromyalgia / Q000175:diagnosis / Q000503:physiopathology*; D006801:Humans; D008875:Middle Aged; D009126:Muscle Relaxation; D010146:Pain / Q000175:diagnosis / Q000503:physiopathology*; D011187:Posture; D014911:Whiplash Injuries / Q000175:diagnosis / Q000503:physiopathology*