Comparative Study On Biomechanical Characteristics Of Deep Jump On Different Surfaces By Athletes Of Different Levels

PURPOSES:In drop jump training,different surface hardness,material and stability will affect the effect of drop jump training and the risk of injury.Therefore,this study compares four common surface jumps in hard ground(force platform),sand,gymnastics mat and balance mat by means of sports biomechanics.Analyze the difference of injury risk and training benefit of different level trainer in different material surface diving,so as to make the trainer more reasonable to use in practice.METHODS: Twenty-seven students from Physical Education College of Zhejiang Normal University were recruited,including 11 subjects(excellent group)who had level 2 or above in short,cross and jump events of track and field,and 16subjects(ordinary group)who had level 2 or below.During the experiment,subjects visited the laboratory for three times,each time with an interval of 1-2 days.The first two times were for adaptive exercise,and the last time was for formal test.Each surface was repeated three times at a height of 45 cm,with a 30-second interval of 3minutes for each surface.The order of the four surface jumps is load bench → balance pad → gymnastics pad → sandy land.The recovery coefficient of load bench is e=0.82,balance pad is e=0.75,gymnastics pad is e=0.63,and sandy land is e=0.1.A three-dimensional force measuring table was used to obtain dynamic data,with a sampling frequency of 250 Hz and a sampling time of 4 seconds.Two SONY DCRHC52 E digital cameras were used to obtain Motion images,and the shooting frequency was 50 frames/second.The 3D Motion resolution system of Germany,SIMI-Motion,was used to analyze the movements of the subjects and obtain the kinematic data.RESULTS:(1)In terms of kinematic parameters,there is no interaction between the landing time between the motion level and the moving surface,the height and velocity of the center of gravity,the change of joint Angle,and the peak angular velocity of the joint.The comparison between the two groups showed that,compared with the ordinary group,the excellent group of the four materials had shorter time to touch the ground,smaller changes of joint angular velocity and joint Angle in the buffer period,and larger changes of joint angular velocity,joint Angle and center of gravity height and velocity in the push period.The comparison of the four surface materials showed that in terms of the touching time,the excellent group was consistent with the common group,which showed that the digging time of the sand drop jump was longer than the other three surface materials.In the center of gravity,the velocity and height of the center of gravity jump of the excellent sand group and the common sand group were lower than those of the other three kinds of surface.In terms of the change of joint Angle,the hip and knee joint Angle of the normal group were less changed during the deep jump cushion stage,and the two groups showed consistent that the change of ankle joint Angle increased with the decrease of the ground recovery coefficient.The peak value of ankle joint angular velocity in the excellent group was significantly higher than that of the other three kinds of surfaces in the sand drop jump and extension period,and the two groups showed that the peak value of knee joint angular velocity in the gymnastics pad drop jump was lower than that of the other three kinds of surfaces in the push and buffer period.(2)In terms of dynamic parameters,there is no interaction between the motion level and the moving surface in the period of drop jump push and buffer,Fz,Fx and Fy.The comparison between the two groups showed that Fz,Fx and Fy of the four surface drop jump elongation periods in the excellent group were all higher than those in the ordinary group,and the difference of buffer force value was small.The comparison of the four surface materials showed that,on Fz,the common group and the excellent group showed that the drop jump push force value of the sand was lower than the other three surface,and the drop jump buffer force value of the force measuring table was lower than the other three surface.On Fy,the Fy values of the four kinds of surface drop jump buffer periods of the ordinary group and the excellent group are consistent,and the descending order is load-measuring table—gymnastic pad—balance pad—sandy land.On Fx,the force values of the normal group are higher than those of the other three kinds of surfaces in the drop jump buffer period and the push period.On the Fz force-time curve,there is one jump peak of balance pad and gymnastic pad,two jump peaks of load measuring table,and three jump peaks of sand.On the Fy-time curve,only the first trough of the force-measuring platform jumps lower than the second trough,which occurs at the moment of landing.CONCLUSION :(1)The stepping ability and impact resistance of the excellent group are stronger than that of the ordinary group,and the non-contact injury risk of the ordinary group is higher than that of the excellent group.Balance MATS,exercise MATS,and sand all helped reduce the risk of non-contact injury in both groups,with sand having the best effect.(2)The lower the surface recovery coefficient,the greater the stimulation to the peripheral muscles of the ankle,which is conducive to the improvement of the strength and stability of the ankle.The balance and exercise pads improve the step fluency of the drop jump,while the sand reduces the step fluency relative to the bench drop jump.