title: Active therapy for chronic low back pain: part 2. Effects on paraspinal muscle cross-sectional area, fiber type size, and distribution.
abstract: METHODS
  Randomized prospective study to compare the effects of three types of active therapy on the back muscle structure of chronic low back pain patients.
  
  
  OBJECTIVE
  To analyze the effects of 3 months active therapy on gross back muscle size and muscle fiber type characteristics and their relationship to changes in muscle function.
  
  
  BACKGROUND
  Many studies have documented a diminished muscular performance capacity in cLBP patients, but few have supported this with evidence of alterations in either the macro- or microscopic structure of the paraspinal muscles. Investigations of the changes in muscle structure following active rehabilitation are even rarer.
  
  
  METHODS
  Assessments of trunk muscle cross-sectional area (using MRI), erector spinae fiber size/type distribution and pathology (percutaneous biopsy), and muscle function (see Part 1) were made in a group of 59 individuals with cLBP, who were participating in a randomized trial of active therapies for cLBP (physiotherapy, muscle training on devices, aerobics).
  
  
  RESULTS
  Fifty-three out of 59 patients (90%) completed the therapy. At baseline, significant correlations were observed between the size of the paraspinal muscles and isometric back extension strength (P=0.0001), and between the proportional area of the muscle occupied by each fiber type and the fatigability of the muscle (P=0.012). Following therapy, there were small (few percent) increases in trunk muscle size in the aerobics and physiotherapy groups and a similarly slight decrease in the devices group. Changes in erector spine size correlated only weakly and nonsignificantly with changes in back extension strength. There were no major changes in fiber type proportion or fiber size in any group following therapy.
  
  
  CONCLUSIONS
  Three months active therapy is not sufficient to reverse the typical "glycolytic" profile of the muscles of cLBP patients or to effect major changes in backmuscle size. The alterations in muscle performance observed (increased strength and endurance; Part 1) werenot explainable on the basis of structural changes within the muscle.
authors.affiliation: Department of Neurology, Schulthess Klinik, Zürich, Switzerland. lkaeser@anatom.unizh.ch
authors.forename: L
authors.initials: L
authors.lastname: Käser
authors.forename: A F
authors.initials: AF
authors.lastname: Mannion
authors.forename: A
authors.initials: A
authors.lastname: Rhyner
authors.forename: E
authors.initials: E
authors.lastname: Weber
authors.forename: J
authors.initials: J
authors.lastname: Dvorak
authors.forename: M
authors.initials: M
authors.lastname: Müntener
mesh_terms: D000328:Adult; D001706:Biopsy; D048429:Cell Size; D002908:Chronic Disease; D005260:Female; D006801:Humans; D017116:Low Back Pain / Q000473:pathology* / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D018763:Muscle Fatigue; D018485:Muscle Fibers, Skeletal / Q000473:pathology*; D018482:Muscle, Skeletal / Q000473:pathology* / Q000502:physiology; D026741:Physical Therapy Modalities; D011446:Prospective Studies; D012038:Regeneration