title: Patellofemoral joint stress during weight-bearing and non-weight-bearing quadriceps exercises.
abstract: METHODS
  Single-group, repeated-measures design.
  
  
  OBJECTIVE
  To compare patellofemoral joint (PFJ) stress among weight-bearing and non-weight-bearing quadriceps exercises.
  
  
  BACKGROUND
  An important consideration when prescribing exercises to strengthen the quadriceps in persons with patellofemoral pain is to minimize PFJ loading. Currently, there is disagreement in the literature as to which exercises and ranges of motion best accomplish this goal.
  
  
  METHODS
  Ten healthy subjects participated. Lower extremity kinematics, kinetics, and electromyography of the knee musculature were obtained during a weight-bearing squatting exercise and 2 non-weight-bearing knee extension exercises: (1) knee extension with variable resistance, and (2) knee extension with constant resistance. A previously described biomechanical model was used to estimate PFJ stress at 0°, 15°, 30°, 45°, 60°, 75°, and 90° of knee flexion. PFJ stress was compared among the 3 exercises using a 2-way analysis of variance with repeated measures.
  
  
  RESULTS
  Compared to the 2 non-weight-bearing exercises, the squat exercise produced significantly higher PFJ stress at 90°, 75°, and 60° of knee flexion. Conversely, the 2 non-weight-bearing exercises produced significantly higher PFJ stress at 30°, 15°, and 0° of knee flexion when compared to the squat exercise. The knee-extension-with-variable-resistance exercise produced significantly lower PFJ stress than the knee-extension-with-constant-resistance exercise at 90°, 75°, and 60° of knee flexion.
  
  
  CONCLUSIONS
  To minimize PFJ stress while performing quadriceps exercises, our data suggest that the squat exercise should be performed from 45° to 0° of knee flexion and the knee-extension-with-variable-resistance exercise should be performed from 90° to 45° of knee flexion.
authors.affiliation: Jacquelin Perry Musculoskeletal Biomechanics Research Laboratory, Division of Biokinesiology and Physical Therapy, University of Southern California, Los Angeles, CA.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Powers
authors.forename: Kai-Yu
authors.initials: KY
authors.lastname: Ho
authors.forename: Yu-Jen
authors.initials: YJ
authors.lastname: Chen
authors.forename: Richard B
authors.initials: RB
authors.lastname: Souza
authors.forename: Shawn
authors.initials: S
authors.lastname: Farrokhi
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D008297:Male; D053580:Muscle Strength / Q000502:physiology; D057071:Patellofemoral Joint / Q000502:physiology*; D052097:Quadriceps Muscle / Q000502:physiology*; D016059:Range of Motion, Articular; D055070:Resistance Training; D013314:Stress, Mechanical; D016474:Weight-Bearing; D055815:Young Adult