Biomechanical Characteristics Of Above-water Phase Of Kick Start In Swimming

This study aimed to determine the key biomechanical parameters of the water part of kick start through the biomechanical analysis for the above-water part of kick start.Find the biomechanical characteristics of the above-water part of kick start by the analysis of dynamics and kinematics.Methods:Twenty-six male swimmers who are from China national swimming team participated in this study.The Performance Analysis System of Swimming was used in the trials,which was divided into two parts:force and video.In the force part,force platform and sensors are used to obtain the ground reaction force of front leg,ground reaction force of rear leg and grab force respectively,and the acquisition frequency is 500Hz.Vertical and horizontal ground reaction force is composed,and then the impulse and power are calculated.In the video part obtains the video from starting signal until the swimmer’s head crosses the 15m mark,and the acquisition frequency is 100Hz.The software of Kistler test system is used to analyze the underwater video and determine the segmentation time.The two-dimensional coordinates of the motion center of the joint are obtained by using the plane fixed-point analysis of the Shixun video analysis system,and the Butterworth low-pass filter with the cut-off frequency of 8Hz is performed.The angle and angular velocity of shoulder,hip and knee were calculated by the two-dimensional coordinates of joint center.Pearson correlation was used to test the relationship between parameters and starting performance;principal component analysis was used to determine the key parameters;multiple linear regression analysis was used to reduce the number of parameters.Finally,combined with kinematics and dynamics,the biomechanical characteristics of kick start are analyzed.Results:1.The movement mode of the front and rear knee joints on the squatting platform is different,the front knee joint flexes first and then extends(the minimum is 103.5±7.8°),and the rear knee joint extends directly(the starting angle is 87.53±8.39°);2.In the above-water part of kick start,the front leg produces 1.63±0.29Ns/BM horizontal impulse and 5.51±0.77Ns/BM vertical impulse;the rear leg produces 2.81±0.22Ns/BM horizontal impulse and 3.05±0.25Ns/BM vertical impulse;hand produces 0.06±0.21Ns/BM horizontal and-2.06±0.63Ns/BM vertical impulse;3.The average horizontal force,average power and average acceleration are strongly correlated with the time of 5m,10m and 15m(|R|>0.6);4.Principal component analysis is used to extract six principal components with complementary correlation,and the cumulative contribution rate of variance is 90.69%;5.The regression model of 5m time includes average acceleration,water entry time,hip angular velocity and horizontal impulse(R2=0.93,P<0.01 5);the regression model of 10m time includes average horizontal force and average power(R2=0.65,P<0.035);the regression model of 15m time includes average power and hip angular velocity(R2=0.607,P<0.011);.Conclusions:1.The kick start technique is that it does not produce high vertical take-off velocity on block phase,but uses more physical ability to produce horizontal take-off velocity;2.On-block phase of kick start,the front leg and rear leg have different roles.The rear legs produce the main horizontal impulse(rear leg:62.18%of the horizontal impulse,front leg:36.06%of the horizontal impulse,and grab:1.7%of the horizontal impulse).And the front legs produce the main vertical impulse;3.Average horizontal force,average power and average acceleration are the key parameters to evaluate the starting performance of swimming.