title: The Effect of Altering Knee Position and Squat Depth on VMO : VL EMG Ratio During Squat Exercises.
abstract: BACKGROUND
  Patellofemoral pain syndrome is an extremely common condition, believed to be caused by altered activation of vastus medialis obliquus (VMO), leading to maltracking of the patella.
  
  
  OBJECTIVE
  This study aimed to investigate the effect of altering knee movement and squat depth on the ratio of VMO and vastus lateralis (VMO : VL) during squat exercises.
  
  
  METHODS
  Eighteen (7 male and 11 female) healthy, asymptomatic participants performed semi-squat exercises with three squat depths (20°, 50° and 80° of knee flexion) while following three knee movement paths (neutral, varus or valgus). Normalized VMO : VL ratio from linear envelope surface electromyography was analysed.
  
  
  RESULTS
  No significant effect was found for gender (p = 0.87), leg dominance (p = 0.99) or knee position (p = 0.44). A significant effect was found for squat depth (p < 0.001) with both the 50° and 80° squats showing increases in VMO : VL ratio (p = 0.031 and p = 0.028), respectively. The VMO : VL ratio was not influenced by gender, leg dominance or knee position in semi-squat exercises.
  
  
  CONCLUSIONS
  Increases in relative VMO activation did occur in 'deeper' squat depths (50° and 80° knee flexion) compared with the 20° condition. Further research is needed in this area concerning the effects of such exercise modifications on a symptomatic patellofemoral pain syndrome population. Copyright © 2015 John Wiley & Sons, Ltd.
authors.affiliation: Department of Physiotherapy, Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, Australia.
authors.forename: Shapour
authors.initials: S
authors.lastname: Jaberzadeh
authors.affiliation: Physica Devonport Physiotherapy, Devonport, Australia.
authors.forename: Daniel
authors.initials: D
authors.lastname: Yeo
authors.affiliation: Department of Medicine (Royal Melbourne Hospital), The University of Melbourne, Melbourne, Australia.
authors.forename: Maryam
authors.initials: M
authors.lastname: Zoghi
mesh_terms: D000886:Anthropometry; D001696:Biomechanical Phenomena; D015444:Exercise / Q000502:physiology*; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D046788:Patellofemoral Pain Syndrome / Q000503:physiopathology; D052097:Quadriceps Muscle / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology*; D055815:Young Adult
keywords: patellofemoral joint; squat exercises; vastus lateralis; vastus medialis obliquus