Sports Biomechanics Study On Jumping Phase Of Volleyball Spike Action On Sand-ground Performed By Excellent Volleyball Sportsmen

Spike technique consists of a set of consecutive parts of preparation gesture,approach,jumping hitting volleyball in the air and landing etc. ,and it is one of the basic techniques with violent attack in indoor volleyball as well as in beach volleyball.Because of the difference of match rule,it's more important to beach volleyball.Beach volleyball match must be carried out on soft and fine sand of at least 40cm deep with the nature of being flowing and being compressive,so it's difficult to keep the gravity centre of human body stable when sportsman moves on the sand-ground,and the above features directly spoil the quality of the two critical phases of approach and jumping It's not rational to apply to the beach volleyball directly with indoor jumping technique.This paper firstly studied mechanics transferring functions of the sand experimentally with the theory of "black-box",and secondly on this basis we analyzed the technique features and dynamic principles of jumping phase of volleyball spike on the sand-ground through measuring kinematics and kinetics data synchronically.We selected "achieving maximum height" as logic goal,the theory of vertical jumping as study bases,study on jumping phase of volleyball spike on hard-ground as a contrast,and then discussed the inherent logics of kinematics parameters and kinetics parameters as well as interrelationships and external principles on the effect of jumping on sand-ground according to logic sequences of parts interpreting whole body,velocity interpreting displacement,kinetics interpreting kinematics and dynamics mechanism interpreting technique features.Eight subjects were volunteered to participate in the experiment including two parts,i.e. drop-jumping and spike technique.The former was carried out with force-conductor (HT-100,512Hz) and three-dimentional force plate (200Hz) and the latter with normal-speed videotape(50Hz) and three-dimentional force plate Simultaneously,respectively.We made a 3 X 1 X 0.4m sand-ground to simulate the ground for formal beach volleyball match.By the analysis of experiments,we concluded:l.Sand mechanics transferring specific propertiesl)The theory of "black-box",out of system,is an effective means for studying sand mechanics transferring specific properties;the experiment of "drop-jumping",one of the variable input style to the "black-box",makes the study of sports biomechanics more alive.2)Sand (about 40cm deep) force transferring function and impulse transferring function are Fd=0.39Fu1.16 and Id=0.88Iu ,respectively.2.The technique features of jumping phase of volleyball spike on the sand-groundl)The phase features of jumping on the sand-ground: the during of jumping is relatively long,definitely including acceleration flexion phase;both deceleration flexion phase and acceleration extending phase are two main phases,and the relatively smallproportion of the latter phase is the critical factor influencing phase structure.2)The human body gravity centre action features of jumping phase of volleyball spike on the sand-ground:the horizontal velocity loss of gravity centre during whole course and vertical displacement in acceleration extending phase as well as vertical velocity at takeoff are all small,so there is a small angle of takeoff.3)The human body segment action features of jumping phase of volleyball spike on the sand-ground:(l)the action principles of right ankle is that there are small dorsiflexion amplitude in deceleration phase and big dorsiflexion amplitude in acceleration extending phase.The former is for crushing sand and the latter makes vertical velocity of gravity centre small at takeoff.(2)The stretching principle of joints of hip,knee and ankle of body lateral is in accordance with the sequencing principle of proximal-to-distal,but both hip and knee initiate earlier to spoil the consecution of the three joints of lower limbs.(3)All joints of right lateral basically attain maximum angular velocity simultaneously at takeoff,but there is a trend to non-simultaneousness and shoulder joint initiates earlier to destroy...