title: Ankle positioning and knee perturbation affect temporal recruitment of the vasti muscles in people with patellofemoral pain.
abstract: OBJECTIVE
  To compare the temporal recruitment of the vastus medialis obliquus (VMO) and vastus lateralis (VL) during voluntary ankle movements and perturbed standing in people with patellofemoral pain, and to determine the effects of different reflex and voluntary postural exercise tasks on VMO facilitation.
  
  
  METHODS
  Repeated-measures design.
  
  
  METHODS
  Twenty-three subjects with patellofemoral pain.
  
  
  METHODS
  Quadriceps reflex contraction in response to postero-anterior knee perturbations was measured with three crural muscle contraction conditions and three postural exercises (semi-squatting, tip-toeing and heel standing).
  
  
  METHODS
  The electromyographic (EMG) onset time of the VMO and VL during each task was measured and compared across the different tasks.
  
  
  RESULTS
  The mean EMG onset time of the VMO was later than that of the VL in the voluntary tasks such as tip-toeing (VMO 95.3ms vs VL 36.4ms, mean difference 58.9ms, 95% confidence interval -33.7 to 151.5ms), whereas earlier VMO activation was found in the perturbation tests such as toe standing (VMO 17.6ms vs VL 22.9ms, mean difference -5.3ms, 95% confidence interval -25.3 to 14.7ms).
  
  
  CONCLUSIONS
  These findings suggest the potential benefits of unexpected perturbation activities for facilitating VMO activation. The clinical applications of perturbation tasks in rehabilitation exercise programmes and the underlying mechanisms warrant further investigation.
authors.affiliation: Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hung Hom, Hong Kong.
authors.forename: Elton C T
authors.initials: EC
authors.lastname: Ng
authors.forename: Mara P Y
authors.initials: MP
authors.lastname: Chui
authors.forename: Aggie Y K
authors.initials: AY
authors.lastname: Siu
authors.forename: Vaniel W N
authors.initials: VW
authors.lastname: Yam
authors.forename: Gabriel Y F
authors.initials: GY
authors.lastname: Ng
mesh_terms: D000328:Adult; D000842:Ankle; D003430:Cross-Sectional Studies; D004576:Electromyography; D005081:Exercise Therapy / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D010146:Pain / Q000534:rehabilitation*; D057071:Patellofemoral Joint / Q000503:physiopathology*; D056888:Patient Positioning; D004856:Postural Balance; D052097:Quadriceps Muscle / Q000503:physiopathology*