Comparative Analysis On The Joint Angle Of Freestyle Kicking Action Of Swimmers At Different Levels

Objective: Freestyle leg movement is relatively simple,but it requires a high degree of control.Because of its large movement area and great resistance to confrontation,it has become the constant pursuit of the industry to require more efficient freestyle leg and less resistance to confrontation.Moreover,the thrust generated by freestyle leg drawing water is 36.5% of the thrust of freestyle complete coordination technology,and freestyle leg can also keep the body floating in water,so as to achieve the purpose of more horizontal body posture and less resistance.Therefore,the research on freestyle leg is particularly important,and the application of freestyle leg technology also reflects the technical level of athletes,and also has a profound impact on the outcome of their competition.While consulting the literature,it is found that the research on freestyle leg mainly focuses on its teaching methods,while the analysis of movements is relatively less,so it is particularly important to use multimedia technology to study freestyle leg movements underwater.Methods: Thirty-three athletes of different grades(Grade I,Grade II and below Grade II)were selected as experimental subjects and divided into experimental group A(Grade I)5,control group B(Grade II)14 and control group C(below Grade II)14.An underwater high-speed camera is used for fixed-point shooting,and the data of athletes’ round trips are collected.Then Dartish8.0 analysis software is used to get the data of joint angle and movement cycle of each athlete.Finally,Excel and Spss software are used to analyze the data,and the average value and variance of each joint angle and the data difference of each group are obtained.Finally,the horizontal comparative analysis is carried out.Results:(1)In kick-down,the hip angle of experimental group A is about 173～164 degrees,that of control group B is about 172～164 degrees,that of control group C is about170～163 degrees,and the hip angle of experimental group A is the largest.The most obvious difference among the three groups lies in the initial angle of hip joint,with z values of 1.05 and 1.34.In the kick,the knee angle of the three groups of athletes can be kept at about 160 degrees,but the deviation range between the experimental group A and the control group B can be minimized.The end angle of experimental group A is about 177 degrees,which is close to a right angle,which can effectively reduce the water resistance,while the end angle of control group B and control group C is relatively small,which not only can not reduce the resistance,but also can reduce the effective working distance,thus greatly weakening the thigh efficiency.In the kick-kick stage,the ankle joint of the experimental group A changed little,basically maintained at about 171 degrees and the movement angle was about 3 degrees,while the ankle joint angles of the control group B and the control group C were relatively small,both at about 168 degrees,which was 3 degrees less than that of the experimental group A.(2)The average time spent in the lower kick was 0.12 seconds in experimental group A,0.13 seconds in control group B,0.14 seconds in control group C,and the slowest in control group C.The average time of lifting link in experimental group A was 0.11 seconds,that in control group B was 0.12 seconds,and that in control group C was 0.11 seconds.In terms of overall time,the average total time for the experimental group A,the control group B and the control group C was 0.22 seconds,0.24 seconds and 0.26 seconds respectively.Conclusion:(1)When kicking down,the angle of hip joint in the experimental group is generally larger than that in the control group,which indicates that the force exerted by hip joint in the experimental group is more obvious,and the force distance is larger,which can fully kick.At the same time,the angle data of the experimental group is relatively concentrated,while that of the control group is relatively scattered.Moreover,when the experimental group and the control group kick under the hip joint,the biggest difference lies in the initial angle.The initial angle of knee joint of control group C is the largest,while experimental group A and control group B are closer,and the angle is smaller than that of control group C,which indicates that the main force point of control group C is knee joint,not hip joint,and the difference of initial angle of knee joint among the three groups of athletes is also the largest.The ankle joint angle of experimental group A is the largest,almost right angle,which can effectively increase the water drawing area and improve the propulsive force,followed by control group B,while the ankle joint angle of control group C is relatively smal(2)The main difference between experimental group A,control group B and control group C in freestyle kicking is the hip joint and knee joint.Experimental group A can better exercise the hip joint and drive the lower leg to kick,while control group C has a smaller range of hip joint movement,and mainly uses the knee joint to drive the lower leg to kick.(3)In the aspect of movement stability,the athletes in the experimental group A have relatively uniform movements,and the completion rate of one cycle movement is high,which can guarantee the perfect completion of one exercise cycle.The movement stability of control group B and control group C is confused and the completion rate is not high.Experimental group A has the shortest exercise cycle,the highest kick frequency and the most thigh times per unit time.In control group B,the exercise cycle was longer.