Abstract: BACKGROUND: Standing long jump is a standard action often used in human body jumping, and it is also one of the main items of lower limb explosive force training. A large number of studies have shown that the arms swing movement in the take-off process and the use of the toe-out posture of the foot when touching the ground can increase the jumping distance, but few studies have paid attention to the knee joint injury during the touchdown process. 
OBJECTIVE: To study the stress distribution characteristics of the bilateral meniscus and femoral cartilage under different arm swinging modes and touchdown postures in standing long jump. 
METHODS: Eight male college students were recruited for the standing long jump test. The kinematic data and ground reaction force were collected under the condition of free and limited swing arms, ankle joint normal posture and toe-out posture touching the ground. The knee reaction force was obtained as the boundary condition and load by inverse dynamic calculation. Based on the MRI images of a subject's knee joint, a three-dimensional finite element model of the knee joint was established to simulate the landing process of a standing long jump. 
RESULTS AND CONCLUSION: (1) There was an interaction between arm swing and ankle posture on knee kinematics. Limiting the swing arm and changing the contact posture of the ankle joint would have a significant impact on the kinematics characteristics of the knee joint in the sagittal plane and frontal plane (P < 0.001, P < 0.001). (2) When the limited swing arm + normal posture touchdown and the free swing arm + normal posture touchdown, the bilateral cartilage contact was more uniform. The stress concentration of the limited swing arm + toe-out posture touchdown and the free swing arm + toe-out posture touchdown occurred on the inner side of the cartilage and the stress on the outer side was less. The inner cartilage was more impacted than the outer side. The peak contact stresses of femoral cartilage (8.89 MPa) and meniscus (10.71 MPa) were lower when the swing arm combined with toe-out touched the ground, while the peak contact stresses of femoral cartilage (13.11 MPa) and meniscus (11.23 MPa) were higher when the swing arm combined with toe-out was limited. (3) These findings indicate that the correct arm swing and the appropriate toe-out posture landing can reduce the risk of knee joint injury. When the ankle joint touches the ground in toe-out posture and limits the arm swing during jumping, the contact stress of the femoral cartilage will be significantly increased, possibly increasing the risk of knee joint injury.

Key words: standing long jump, motor control, swing arm action, finite element analysis, knee joint injury