title: Determining the activation of gluteus medius and the validity of the single leg stance test in chronic, nonspecific low back pain.
abstract: OBJECTIVE
  To determine the activation of the gluteus medius in persons with chronic, nonspecific low back pain compared with that in control subjects, and to determine the association of the clinical rating of the single leg stance (SLS) with chronic low back pain (CLBP) and gluteus medius weakness.
  
  
  METHODS
  Cohort-control comparison.
  
  
  METHODS
  Academic research laboratory.
  
  
  METHODS
  Convenience sample of people (n=21) with CLBP (>12wk) recruited by local physiotherapists, and age- and sex-matched controls (n=22). Subjects who received specific pain diagnoses were excluded.
  
  
  METHODS
  Not applicable.
  
  
  METHODS
  Back pain using the visual analog scale (mm); back-related disability using the Oswestry Back Disability Index (%); strength of gluteus medius measured using a hand dynamometer (N/kg); SLS test; gluteus medius onset and activation using electromyography during unipedal stance on a forceplate.
  
  
  RESULTS
  Individuals in the CLBP group exhibited significant weakness in the gluteus medius compared with controls (right, P=.04; left, P=.002). They also had more pain (CLBP: mean, 20.50mm; 95% confidence interval [CI], 13.11-27.9mm; control subjects: mean, 1.77mm; 95% CI, -.21 to 3.75mm) and back-related disability (CLBP: mean, 18.52%; 95% CI, 14.46%-22.59%; control subjects: mean, .68%; 95% CI, -.41% to 1.77%), and reported being less physically active. Weakness was accompanied by increased gluteus medius activation during unipedal stance (R=.50, P=.001) but by no difference in muscle onset times. Although greater gluteus medius weakness was associated with greater pain and disability, there was no difference in muscle strength between those scoring positive and negative on the SLS test (right: F=.002, P=.96; left: F=.1.75, P=.19).
  
  
  CONCLUSIONS
  Individuals with CLBP had weaker gluteus medius muscles than control subjects without back pain. Even though there was no significant difference in onset time of the gluteus medius when moving to unipedal stance between the groups, the CLBP group had greater gluteus medius activation. A key finding was that a positive SLS test did not distinguish the CLBP group from the control group, nor was it a sign of gluteus medius weakness.
authors.affiliation: Eastern Health Authority, St. John's, Newfoundland and Labrador, Canada.
authors.forename: Tracy
authors.initials: T
authors.lastname: Penney
authors.affiliation: Recovery and Performance Laboratory, Physical Medicine & Rehabilitation, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada.
authors.forename: Michelle
authors.initials: M
authors.lastname: Ploughman
authors.affiliation: Recovery and Performance Laboratory, Physical Medicine & Rehabilitation, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada.
authors.forename: Mark W
authors.initials: MW
authors.lastname: Austin
authors.affiliation: School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada.
authors.forename: David G
authors.initials: DG
authors.lastname: Behm
authors.affiliation: School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada. Electronic address: jmbyrne@mun.ca.
authors.forename: Jeannette M
authors.initials: JM
authors.lastname: Byrne
mesh_terms: D000328:Adult; D002081:Buttocks; D016022:Case-Control Studies; D059350:Chronic Pain / Q000503:physiopathology*; D004185:Disability Evaluation; D004576:Electromyography; D005080:Exercise Test; D005260:Female; D006801:Humans; D017116:Low Back Pain / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D009119:Muscle Contraction / Q000502:physiology; D053580:Muscle Strength; D018908:Muscle Weakness / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology*; D010147:Pain Measurement
keywords: Buttocks; Chronic pain; Electromyography; Low back pain; Muscle strength; Physical therapy modalities; Rehabilitation