Objective To explore the effect of gait biomechanics on sports injuries in middle-and long-distance teenage runners.Methods Eighteen healthy middle-and long-distance runners were select-ed as subjects,and the biomechanics of their gait during mid-speed running was tested using a three-dimensional infrared motion capture system,a three-dimensional force measurement platform,and a la-ser speed measurement system.After the test,data on sports injuries within one year were collected.Based on the severity of their injuries,the athletes were divided into an injury group,and a non-inju-ry group(healthy group).Their gait spatiotemporal parameters,ground reaction forces,and independent sample t-test for trunk and lower limb joint angles,and lower limb joint power were all analyzed.Re-sults There was no significant difference in the spatiotemporal parameters of the mid-speed running gait and ground reaction force indicators between the two groups(P>0.05).The maximum trunk exten-sion angle of the injury group was significantly greater than the healthy group(P<0.05),while the max-imum trunk flexion angle was significantly smaller than the latter(P<0.05).Moreover,the maximum right flexion angle,hip adduction angle,maximum hip adduction angle,ankle varus angle and ankle internal rotation angle of the injury group were significantly smaller than that of the healthy group,with the ankle internal rotation angle significantly bigger than the latter(P<0.05 for all).Meanwhile,the maximum hip joint extension power of the injury group was significantly lower than the healthy group(P<0.05),while the maximum knee joint abduction power was significantly higher than the latter group(P<0.01).Conclusion When running at medium speed,the spatiotemporal parameters of the sup-porting leg and ground reaction force have a relatively smaller impact on lower limb sports injuries of adolescent middle-and long-distance runners,while a greater degree of trunk tilt back,a smaller right flexion angle,a smaller hip joint adduction of the supporting leg,a smaller internal rotation an-gle when the ankle joint is on the ground,and a higher internal rotation angle when the ankle joint is off the ground make the lower limbs more prone to sports injuries.Moreover,such runners with low-er hip joint extension power and higher knee joint abduction power in their support legs are more like-ly to suffer from lower limb injuries.