The goal of this study was to quantify differences in patellofemoral joint stress which may occur when healthy runners alter their foot strike pattern from their habitual rearfoot strike to a forefoot strike in order to gain insight on the potential etiology and treatment methods of patellofemoral pain. Sixteen healthy female runners completed twenty 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. Peak patellofemoral joint stress and the stress-time integral over stance phase decreased 27% and 12%, respectively, in the forefoot strike condition (p<0.001). Peak vertical ground reaction force rose slightly in the forefoot strike condition (p<0.001). Peak quadriceps force and average hamstring force decreased while gastrocnemius and soleus muscle forces was raised 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 didn't change between conditions (p=0.375), however 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).
Altering one's strike pattern to a forefoot strike produces consistent reductions in patellofemoral joint stress independent of changes in step length. Thus, implementation of forefoot strike training programs may be suggested in the treatment of runners with patellofemoral pain. Although it is recommended that the transition to a forefoot strike pattern be completed in a graduated fashion.