title: Electromechanical delay of the vastus medialis obliquus and vastus lateralis in individuals with patellofemoral pain syndrome.
abstract: METHODS
  Case-control study.
  
  
  OBJECTIVE
  To examine electromechanical delay (EMD) of the vastus medialis obliquus (VMO) and the vastus lateralis (VL) in individuals with patellofemoral pain syndrome (PFPS).
  
  
  BACKGROUND
  EMD is a mechanical property of muscles related to protective reflex and sports performance. The time duration of the EMD can be shortened with strength training and, conversely, can be lengthened secondary to immobilization. However, it is unclear if EMD between various components of the quadriceps is affected in individuals with PFPS.
  
  
  METHODS
  Twenty-six individuals with PFPS and 26 healthy volunteers were studied. The VMO and VL were electrically stimulated to evoke muscle twitches. Ultrasound was used to assess patellar movement elicited by the muscle twitch. The time from the onset of electrical stimulation to the onset of patellar movement was measured as the EMD. The EMDs of the VMO and VL were compared between groups using a mixed-model analysis of variance.
  
  
  RESULTS
  Subsequent to a significant interaction (P<.001), post hoc analysis indicated that the EMD of the VMO was longer (PFPS, 37.3 ± 0.7 milliseconds; control, 25.9 ± 0.7 milliseconds; P<.001) and the EMD of the VL was shorter (PFPS, 18.4 ± 0.5 milliseconds; control, 25.1 ± 0.5 milliseconds; P<.001) in the PFPS group. Therefore, in the individuals with PFPS, the EMD of the VMO was significantly longer than that of the VL (P<.001), which was not the case for those in the control group (P = .20).
  
  
  CONCLUSIONS
  The mechanical properties of the VMO and VL may be altered in patients with PFPS.J Orthop Sports Phys Ther 2012;42(9):791-796, Epub 2 August 2012. doi:10.2519/jospt.2012.3973.
authors.affiliation: Department of Physical Therapy, Hungkuang University, Taichung, Taiwan.
authors.forename: Han-Yu
authors.initials: HY
authors.lastname: Chen
authors.forename: Chia-Chen
authors.initials: CC
authors.lastname: Chien
authors.forename: Shyi-Kuen
authors.initials: SK
authors.lastname: Wu
authors.forename: Jiann-Jong
authors.initials: JJ
authors.lastname: Liau
authors.forename: Mei-Hwa
authors.initials: MH
authors.lastname: Jan
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D046788:Patellofemoral Pain Syndrome / Q000503:physiopathology*; D052097:Quadriceps Muscle / Q000000981:diagnostic imaging / Q000502:physiology*; D014463:Ultrasonography; D055815:Young Adult