The Biomechanical Study Of Lower Extremity Movement Control And Hamstring Muscle Injury Mechanism During Sprinting

Purpose:The purpose of this study was to analyze the movement control of lower extremity by collecting the kinematic, dynamic and EMG data during sprint running. The intersegmental dynamics was introduced into the study to figure out the movement control mechanisms and the loading condition of hamstring muscle, analyze the main torques and muscle activity during lower extremity movement, the main torques of lower extremity were used to study the pattern of movement control and the muscle loading was used to analyze muscle injury mechanism, especially the relationship between hamstring muscle loading and hamstring muscle injury.The CON-TREX Biomechanical Test and Training Systems were used to measure the knee joint torques during isometric contraction and at different isokinetic movement, to study the characteristics and trends of knee joint torques and the muscle force balance condition at different conditions, this will be a window for us to understand the mechanisms of hamstring muscle injury.The significance of this study is that the kinematic, dynamic, isokinetic, EMG data of elite sprinters and intersegmental dynamics were used in the study to research into the mechanisms of movement control and the condition of muscle loading during stance phase and swing phase during sprint running. This would help us to understand movement control, lower extremity muscles'function during the swing and stance phases, furthermore, to provide biomechanical theory for preventing lower extremity muscle injury, rehabilitation therapy and muscle strength training of sprinter.Methods:The CON-TREX Biomechanical Test and Training Systems (Switzerland, type: PM1/MK2a,b), Vicon Motion Analysis System (England, Camera type:MX13), Kistler force plate (Switzerland, type:9287B), Biovisions EMG Measurement System, (Germany, 16 Channels) were selected for this study. The kinematics, dynamics, EMG and isokinetic movement torques data at 0, 60, 120, 180, 240°/s were collected from 8 male elite athletes.Results:During stance phase, the active MUS functioned mainly to counteract the EXF created by the GRF at the knee and hip joint. At the initial phase, the MUS flexed the knee joint and counterbalanced the extension torques of EXF, and the MUS also extended the hip joint and neutralized the flexion torques (EXF) created by the ground reaction forces. During the swing phase, the MUS and MDT at the knee and hip joint functioned for controlling movement of the leg and thigh, causing knee joint flexion from extension and hip joint extension from flexion. The inertial torques produced by leg angular acceleration at the knee and hip joint were the main components of MDT.During initial stance phase and late swing phase, the external torques (EXF, MDT) which were produced by GRF and the segments movement of lover extremity stretched the hamstring muscles to opposite direction at the same time at knee and hip joint. To counterbalance the external torques, the hamstring muscles endured great loading, without considering the effects of external torques at hip joint and the torques which were produced by the knee extensors (quadriceps femoris) and the hip flexors, just at knee joint, the loading of hamstring muscles is more than 10 times of body weight. So the actual torque values which produced by the hamstring muscle at the knee and the hip might be far bigger than the estimated ones. We concluded that when excessive stretching force was applied, especially when powerful muscle contraction was combined with simultaneous forced lengthening of the myotendinous unit, a strain-type injury occurs.According to the peak torques of flexion and extension muscles at knee joint, the data indicated that the flexor and extensor force were an ideal condition, the peak torques of knee flexor were similar to the peak torques of knee extensor at different isokinetic movement speeds. The explosive force indexes of knee flexor were significantly less than the knee extensor explosive force indexes. Maybe this is the key factor which affects the sprint running performance and hamstring muscle injury. The results indicated that by useing the peak torques of knee flexor and extensor to study the balance of knee flexor and extensor is necessary to be investigated. The Rate of Force Development (RFD) enjoyed a great advantage in the judgment of lower extremity muscle explosive force level during high-velocity motion.Conclusion:Inter-segment analysis helped us to further understand muscle's role during sprinting. Muscle torque functioned mainly to counteract the external torques created by the ground reaction force at hip and knee joint during stance phase, its functional role changed during swing phase to mainly counteract movement related torques partially due to the absence of ground reaction forces.The hamstring muscles were stretched by the external torques to opposite directions at the same time at knee and hip joint and endured great loading during initial stance phase and late swing phase. So a hamstring muscle strain injury was more likely to occur during the initial stance phase and the late swing phase of sprint running.The Rate of Force Development (RFD) could reflect the explosive force level difference between knee flexor and extensor during high velocity movement. Maybe this is the key factor which affects the sprint running performance and hamstring muscle injury.