Kinematics And Dynamics Analysis Of The Two Technique Of Swinging Legs For Crouch Start

Purposes:In sprint races such as 60 m and 100 m,in the early stage of the squat start,the athlete usually uses the small knee angle swing technique of swinging leg or the knee low recovery technique to complete the starting.Take the squat start acceleration as the basic target action,exploring athletes using the knee low recovery technology and the small knee angle swing technology.squat starting time of 10 m,the first three steps of kinematic parameters and characteristics,second and third step kinetic parameters and characteristics.Provide a useful reference for athletes in the preferred starting swinging leg technique and training.Method:Eleven sprinters were selected as experimental subjects.each subject completed 4 squat start 10 m acceleration under the conditions of large knee angle swing technique and small knee angle swing technique.use 3 high-speed cameras to collect kinematic data of the first three steps and 10 m times of the athlete's acceleration.Using four Kistler9281 EA dynamometers to collect kinetic data for the second and third steps of the subject.the first three steps of kinematics data are analyzed using shixun software from beijing sport university.10 m times using kinovea0.8.26 analysis.kinetic data was obtained using bioware5.1.0.0 software.calculation and mapping of some parameters using origin pro2018 c software.use excel as a calculation template for some parameters,also organize all the data as a database.Statistical analysis of data using spss19.0.Result:Subjects using the large knee angle swing technique have the following kinematics and dynamics differences compared to the use of the small knee angle swing technique:1)10m starting time is shorter.2)In the first three steps,the minimum knee angle and the average knee angle of the swinging leg are large,the vacant time is short,and the height of the ground and the center of gravity of the ground is low.3)In the first step,the knees at the moment of support from the ground are small and the center of gravity is far away from the ground.4)In the second step,the support time is longer,the support time proportion is larger,and the vacant time proportion is smaller.The knee angle and the corner angle are smaller at the time of leaving the ground,and the center of gravity is far away from the ground.The hip angle is smaller and the center of gravity is at the ground closer.During the support phase,the vertical peak force of the ground is small,the average horizontal and vertical force rate is small,the peak value of the knee extension and the hip extension muscle is small,and the contribution rate of the ankle joint energy release is high.5)The third step is that the support time is longer,the support time is larger,the vacant time is smaller,the stride is smaller,the center of gravity is closer to the ground,and the anteversion angle is larger;In the support phase,the ground vertical force peak is small,the average horizontal and vertical force rate is small,and the peak value of the knee extension muscle is small.The above differences are statistically significant(p < 0.05).Conclusion:1)The subject used the knee low recovery technique to start,has the following advantages,short acceleration time of 10 m,the first three steps have a low center of gravity,large proportion of support-vacancy,can maintain a large torso anteversion.However,there is a greater demand for hip strength in swinging legs.2)The small knee angle swing technique starts with a greater vertical force on the ground,the rate of force and the peak of the knee extension and hip extension,which may be related to the longer vacant time.3)From the contribution rate of the three joints of the support leg,the hip extension muscle group and the knee extension muscle group are the key muscle groups in the special strength training.It is also recommended to increase the proportion of ankle training for athletes who use the knee low recovery technique.4)The corresponding joint angle when the peak of the starting leg muscles appears at the starting support provides a certain reference for the joint special strength training.