Objective:To quantify the effects of different touchdown methods on the knee joint during barefoot running us-ing a validated finite element model of the knee joint,providing a theoretical basis for reducing sports injuries in runners.Method:Kinematics and ground reaction force data were collected from 22 participants during forefoot land-ing,midfoot landing and hindfoot landing at 4 m/s±5％respectively.Knee joint reaction forces were calculated using Visal3D inverse dynamics.The numerical simulations were performed for each of the three ground con-tact processes based on a 3D finite element model of the knee joint.Result:There were significant kinematic differences in the knee joint during forefoot/midfoot touchdown mode and hindfoot touchdown,with a larger peak flexion when using midfoot touchdown.Compared to forefoot touchdown,the midfoot touchdown mode during barefoot running produced a smaller peak in vertical ground reaction force.At the peak vertical ground reaction force,the peak patellofemoral cartilage contact stress(4.83 MPa)and the peak meniscal contact stress(5.98 MPa)in the midfoot touchdown mode were the lowest com-pared to the other two touchdown modes.Conclusion:When running barefoot,using a midfoot landing may reduce the risk of knee injury.It is recom-mended to use the midfoot touch pattern for rehabilitation involving barefoot running.

Objective:To quantify the effects of different touchdown methods on the knee joint during barefoot running us-ing a validated finite element model of the knee joint,providing a theoretical basis for reducing sports injuries in runners.Method:Kinematics and ground reaction force data were collected from 22 participants during forefoot land-ing,midfoot landing and hindfoot landing at 4 m/s±5％respectively.Knee joint reaction forces were calculated using Visal3D inverse dynamics.The numerical simulations were performed for each of the three ground con-tact processes based on a 3D finite element model of the knee joint.Result:There were significant kinematic differences in the knee joint during forefoot/midfoot touchdown mode and hindfoot touchdown,with a larger peak flexion when using midfoot touchdown.Compared to forefoot touchdown,the midfoot touchdown mode during barefoot running produced a smaller peak in vertical ground reaction force.At the peak vertical ground reaction force,the peak patellofemoral cartilage contact stress(4.83 MPa)and the peak meniscal contact stress(5.98 MPa)in the midfoot touchdown mode were the lowest com-pared to the other two touchdown modes.Conclusion:When running barefoot,using a midfoot landing may reduce the risk of knee injury.It is recom-mended to use the midfoot touch pattern for rehabilitation involving barefoot running.

Objective:To analyze the biomechanical characteristics of the knee joint under different lateral cut angles and ground contact modes using the validated finite element model of the knee joint,which provided a theoretical basis for preventing lateral cut sports injuries in football players and formulating rehabilitation training pro-grams after injury. Method:Fifteen male football players(all of whom are national second-level athletes and above)were recruit-ed to perform cutting movements at the angles of 45°,90° and 135° in front and rear touchdown modes at a speed of 6m/s±10％.The kinematics and dynamics data of the knee joint were calculated by Visual 3D soft-ware,and the peak moment of ground reaction force in the six touchdown actions was numerically simulated based on the verified knee joint model. Result:①The cutting angle is positively correlated with the peak knee flexion angle(P＜0.05),indicating that as the cutting angle increases,while vertical ground reaction force decreases significantly with increase cutting angle(P＜0.05).②Significant differences in kinematics and dynamics exist between forefoot and rearfoot strik-ing(P＜0.05).In the forefoot striking mode,there are larger knee flexion angles,external rotation,and inter-nal rotation peak angles,along with higher upward ground reaction force.③At the moment of side cutting contact,the distribution of Von Mises stress in the meniscus and the contact stress in the femoral cartilage show characteristics related to the cutting angle and the mode of foot contact.In the 90° rearfoot striking mode,there is a noticeable concentration of stress on the external edge of the medial meniscus and the medi-al femoral cartilage,which may indicate an increased risk of knee joint injury under these conditions. Conclusion:Performing a 90° cut with a rearfoot striking pattern may lead to an imbalance in internal knee joint stress,particularly causing significant stress concentration on the external edge of the medial meniscus,indicating a higher risk of injury.