title: Performance on the single-leg squat task indicates hip abductor muscle function.
abstract: BACKGROUND
  Contemporary clinical expertise and emerging research in anterior knee pain indicate that treatment of hip muscle function will result in greater effects, if such treatments can be provided to those with hip muscle dysfunction. Thus, it is imperative to develop and evaluate a clinical assessment tool that is capable of identifying people with poor hip muscle function.
  
  
  OBJECTIVE
  The clinical assessment of single-leg squat performance will have acceptable inter- and intrarater reliability. Furthermore, people with good performance on the single-leg squat will have better hip muscle function (earlier onset of gluteus medius activity and greater lateral trunk, hip abduction, and external rotation strength) than people with poor performance.
  
  
  METHODS
  Cohort study (diagnosis); Level of evidence, 2.
  
  
  METHODS
  A consensus panel of 5 experienced clinicians developed criteria to rate the performance of a single-leg squat task as "good," "fair," or "poor." The panel rated the performance of 34 asymptomatic participants (mean ± SD: age, 24 ± 5 y; height, 1.69 ± 0.10 m; weight, 65.0 ± 10.7 kg), and these ratings served as the standard. The ratings of 3 different clinicians were compared with those of the consensus panel ratings (interrater reliability) and to their own rating on 2 occasions (intrarater reliability). For the participants rated as good performers (n = 9) and poor performers (n = 12), hip muscle strength (hip abduction, external rotation, and trunk side bridge) and onset timing of anterior (AGM) and posterior gluteus medius (PGM) electromyographic activity were compared.
  
  
  RESULTS
  Concurrency with the consensus panel was excellent to substantial for the 3 raters (agreement 87%-73%; κ = 0.800-0.600). Similarly, intrarater agreement was excellent to substantial (agreement 87%-73%; κ = 0.800-0.613). Participants rated as good performers had significantly earlier onset timing of AGM (mean difference, -152; 95% confidence interval [CI], -258 to -48 ms) and PGM (mean difference, -115; 95% CI, -227 to -3 ms) electromyographic activity than those who were rated as poor performers. The good performers also exhibited greater hip abduction torque (mean difference, 0.47; 95% CI, 0.10-0.83 N·m·Bw(-1)) and trunk side flexion force (mean difference, 1.08; 95% CI, 0.25-1.91 N·Bw(-1)). There was no difference in hip external rotation torque (P > .05) between the 2 groups.
  
  
  CONCLUSIONS
  Targeted treatments, although considered ideal, rely on the capacity to identify subgroups of people with chronic anterior knee pain who might respond optimally to a given treatment component. Clinical assessment of performance on the single-leg squat task is a reliable tool that may be used to identify people with hip muscle dysfunction.
authors.affiliation: Department of Mechanical Engineering, Melbourne School of Engineering, The University of Melbourne, Melbourne, Australia. k.crossley@unimelb.edu.au
authors.forename: Kay M
authors.initials: KM
authors.lastname: Crossley
authors.forename: Wan-Jing
authors.initials: WJ
authors.lastname: Zhang
authors.forename: Anthony G
authors.initials: AG
authors.lastname: Schache
authors.forename: Adam
authors.initials: A
authors.lastname: Bryant
authors.forename: Sallie M
authors.initials: SM
authors.lastname: Cowan
mesh_terms: D000328:Adult; D015331:Cohort Studies; D005080:Exercise Test / Q000379:methods*; D005260:Female; D006621:Hip Joint / Q000502:physiology* / Q000503:physiopathology; D006801:Humans; D008297:Male; D053580:Muscle Strength / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology* / Q000503:physiopathology; D009135:Muscular Diseases / Q000175:diagnosis* / Q000503:physiopathology; D015203:Reproducibility of Results; D013647:Task Performance and Analysis; D055815:Young Adult