（Key Laboratory of Exercise and Health Sciences of Ministry of Education，Shanghai University of Sport，Shanghai 200438，China)
Abstract: In order to study the biomechanical characteristics of the patellofemoral joint during running, and to probe into the instant effects of running shoes with different minimalist indexes on the contact force and stress etc of the patellofemoral joint, the authors selected 15 healthy male runners who were used to heel landing, respectively wearing running shoes with two minimalist indexes (minimalist running shoes with a minimalist index of 85%, and cushioned running shoes with a minimalist index of 26%), used the Vicon infrared motion capture system and Ki-stler 3D force platform to simultaneously acquire the kinematic data of the knee and ankle joint and ground reaction forces under a running speed of 3.33m/s (speed varying range: ±5%), and calculated quadriceps strength, patel-lofemoral joint contact force, patellofemoral joint contact area, and patellofemoral joint contact stress by means of reverse dynamics etc. The results show the followings: the peak impact forces and peak ground hitting forces under the conditions of the two types of running shoes had no significant differences; as compared to cushioned running shoes, when running with minimalist running shoes: 1) the maximum flexion angle of the knee joint decreased sig-nificantly (P<0.01); 2) the knee joint contact area decreased significantly (P<0.01); 3) the peak torque of the knee joint extensor decreased significantly (P<0.01); 4) the peak values of the patellofemoral joint contact force and stress decreased significantly (P<0.05). This study indicates that as compared to cushioned running shoes, wearing minimalist running shoes significantly decreases patellofemoral joint contact force (by 17.02%) and reduces patel-lofemoral joint contact stress by reducing knee joint extensor torque, while not affecting the peak impact force after ground contracting, thus effectively improving patellofemoral joint loads in the supporting period, and providing a possibility to further reduce the risk of patellofemoral joint pain syndrome.
Key words: sports biomechanics；patellofemoral joint；patellofemoral joint pain syndrome；patellofemoral joint stress；sports shoes