title: Patellofemoral joint stress during running with alterations in foot strike pattern.
abstract: OBJECTIVE
  This study aimed to quantify differences in patellofemoral joint stress that may occur when healthy runners alter their foot strike pattern from their habitual rearfoot strike to a forefoot strike to gain insight on the potential etiology and treatment methods of patellofemoral pain.
  
  
  METHODS
  Sixteen healthy female runners completed 20 running trials in a controlled laboratory setting under rearfoot strike and forefoot strike conditions. Kinetic and kinematic data were used to drive a static optimization technique to estimate individual muscle forces to input into a model of the patellofemoral joint to estimate joint stress during running.
  
  
  RESULTS
  Peak patellofemoral joint stress and the stress-time integral over stance phase decreased by 27% and 12%, respectively, in the forefoot strike condition (P < 0.001). Peak vertical ground reaction force increased slightly in the forefoot strike condition (P < 0.001). Peak quadriceps force and average hamstring force decreased, whereas gastrocnemius and soleus muscle forces increased when running with a forefoot strike (P < 0.05). Knee flexion angle at initial contact increased (P < 0.001), total knee excursion decreased (P < 0.001), and no change occurred in peak knee flexion angle (P = 0.238). Step length did not change between conditions (P = 0.375), but the leading leg landed with the foot positioned with a horizontal distance closer to the hip at initial contact in the forefoot strike condition (P < 0.001).
  
  
  CONCLUSIONS
  Altering one's strike pattern to a forefoot strike results in consistent reductions in patellofemoral joint stress independent of changes in step length. Thus, implementation of forefoot strike training programs may be warranted in the treatment of runners with patellofemoral pain. However, it is suggested that the transition to a forefoot strike pattern should be completed in a graduated manner.
authors.affiliation: Physical Therapy Program, Department of Health Professions, La Crosse Institute for Movement Science, University of Wisconsin - La Crosse, La Crosse, WI.
authors.forename: Charles Nathan
authors.initials: CN
authors.lastname: Vannatta
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Kernozek
mesh_terms: D000293:Adolescent; D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D005528:Foot / Q000502:physiology*; D005684:Gait / Q000502:physiology*; D006801:Humans; D018482:Muscle, Skeletal / Q000502:physiology; D057071:Patellofemoral Joint / Q000502:physiology*; D012420:Running / Q000502:physiology*; D013314:Stress, Mechanical; D055815:Young Adult