Objective To determine the acute effects of heel-to-toe drops(5,0,-11 mm)of running shoes on the loading of the patellofemoral joint and Achilles tendon(AT)in runners with patellofemoral pain(PFP)during running.Methods Sixteen runners with PFP completed a running test while wearing running shoes with different heel-to-toe drops.The retroreflective markers and ground reaction force were measured using an infrared motion capture system and a three-dimensional force plate.The patellofemoral joint stress(PFJS)and AT force were calculated based on biomechanical models of the patellofemoral joint and AT.Results When runners with PFP ran in negative-heel shoes,the PFJS(P<0.001)during 39%-47%of the stance phase,maximum PFJS,and cumulative PFJS(P<0.05)during the stance phase were lower than those in positive-heel shoes.Meanwhile,the AT force(P<0.001)during 12%-46%of the stance phase and cumulative AT force(P=0.001)during the stance phase were larger than those in positive-heel shoes.The AT force(P<0.001)during 12%-31%of the stance phase and cumulative AT force(P=0.023)during the stance phase in negative-heel shoes were higher than those in zero-heel shoes.Conclusions Compared with runners with positive-heel shoes,runners with PFP running in negative-heel shoes had decreased PFJS and cumulative PFJS.This may potentially reduce the risk of further development of PFP.However,compared with zero-and positive-heel shoes,running in negative-heel shoes increases the AT force and cumulative AT force.This may increase the risk of AT injury.Runners with PFP are recommended to undergo acclimatization before shifting to negative-heel shoes.This would limit further progression of PFP without increasing the risk of AT injury.

Objective To determine the acute effects of heel-to-toe drops(5,0,-11 mm)of running shoes on the loading of the patellofemoral joint and Achilles tendon(AT)in runners with patellofemoral pain(PFP)during running.Methods Sixteen runners with PFP completed a running test while wearing running shoes with different heel-to-toe drops.The retroreflective markers and ground reaction force were measured using an infrared motion capture system and a three-dimensional force plate.The patellofemoral joint stress(PFJS)and AT force were calculated based on biomechanical models of the patellofemoral joint and AT.Results When runners with PFP ran in negative-heel shoes,the PFJS(P<0.001)during 39%-47%of the stance phase,maximum PFJS,and cumulative PFJS(P<0.05)during the stance phase were lower than those in positive-heel shoes.Meanwhile,the AT force(P<0.001)during 12%-46%of the stance phase and cumulative AT force(P=0.001)during the stance phase were larger than those in positive-heel shoes.The AT force(P<0.001)during 12%-31%of the stance phase and cumulative AT force(P=0.023)during the stance phase in negative-heel shoes were higher than those in zero-heel shoes.Conclusions Compared with runners with positive-heel shoes,runners with PFP running in negative-heel shoes had decreased PFJS and cumulative PFJS.This may potentially reduce the risk of further development of PFP.However,compared with zero-and positive-heel shoes,running in negative-heel shoes increases the AT force and cumulative AT force.This may increase the risk of AT injury.Runners with PFP are recommended to undergo acclimatization before shifting to negative-heel shoes.This would limit further progression of PFP without increasing the risk of AT injury.