title: Paraspinal muscle function assessed with the flexion-relaxation ratio at baseline in a population of patients with back-related leg pain.
abstract: OBJECTIVE
  The purpose of this study was to assess back muscle status at baseline in patients with back-related leg pain (BRLP) and to correlate those findings with baseline demographic and clinical factors.
  
  
  METHODS
  Surface electromyography (EMG) and electromagnetic motion-tracking detected flexion-relaxation response in 135 patients with BRLP. Surface EMG electrodes were attached with standard skin preparation over the right and left paraspinal muscles at L3. Participants moved from upright standing into full forward flexion, rested flexed for 1 second, and returned to the upright position. A flexion-relaxation ratio (FRR) factor was calculated as the root mean square EMG amplitude during forward flexion divided by the activity at full flexion.
  
  
  RESULTS
  High repeatability was found (intraclass correlation coefficient [ICC]([1,3]) = 0.94 and 0.86) between 3 cycles of assessment at the same session. Patients with BRLP exhibited low FRR values, indicating a loss of the flexion-relaxation response similar to that seen in low back pain patients. Patients with very low FRR had higher Roland-Morris Disability Questionnaire scores than the other patients, had increased incidence of straight leg raise test, and had decreased range and rate of forward flexion.
  
  
  CONCLUSIONS
  A subgroup of patients with BRLP was identified with very low FRR who exhibited more disability and clinical findings and decreased motion. The use of the inverted FRR factor, expressing muscle activity at the fully flexed and resting position as a percentage of peak activity during flexion, provides more stable numerical behavior and another perspective on interpreting FRRs.
authors.affiliation: Chiropractor, Minneapolis, MN, USA. edowens@mindspring.com
authors.forename: Edward F
authors.initials: EF
authors.lastname: Owens
authors.forename: Maruti Ram
authors.initials: MR
authors.lastname: Gudavalli
authors.forename: David G
authors.initials: DG
authors.lastname: Wilder
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D004576:Electromyography; D006801:Humans; D007866:Leg; D017116:Low Back Pain / Q000503:physiopathology*; D008875:Middle Aged; D009126:Muscle Relaxation; D018482:Muscle, Skeletal / Q000503:physiopathology*