| Objective: This article aims atanalyzing characteristics and principles of sports technical movementof back handspring in the phase of upper limb supporting by general means of sport biomechanics from three aspect of kinematics, dynamics and surface electromyography, combined with thecharacteristics of upper limb motor system anatomy toexplore the injury-prone parts and mechanisms in the phase of upper-limb supporting inorder toprovide rationalization proposalforimprovingskills and prevention of sportsinjuries.Methods: Totally 12 college undergraduates of floorexercisespecialabove national secondary reference are selected, wearing close-fitting gym suit of dark color withreflective marker balls ,completing gymnastics back handspring movement in the designated areas in the laboratory. Two high-speed cameras (JVC GC-px100),three-dimensional force platform (AMTI,USA), bio-electrical measuring and analysis system (Biovision,Germany) are used for synchronizing acquisition of kinematic data, kinetic data and surface EMG data of back handspring movementsof the athletes.The joint points displacement, speedand acceleration data plus the joint angle,and angle speed, and angular acceleration data are got through three dimensionalimage analytical system of American Ariel companyAPAS System for editing, digitizing, synthesizing andsmooth processing of the collected images. Vertical groundreaction force, load rate andload attenuation rate data are gotthrough Exce12016 software for general statistics processing and calculus operationof the dynamics data.Origin pro9.0 software is used to calculate the peak impulse of vertical ground reaction force. Dasylab8.0 software is used to filter and full-wave rectify for the acquired EMG signal. Starting and ending positions of upper limb in the phase of supporting are determined by square wave generated by synchronizationtriggers. The time interval is intercepted for integral EMG calculation.Finally, Excel 2016 software data operations are used for sorting, storage and databases, using the Prism 6 software for data analysis and charting.Result:1. The gymnastics back handspring is divided into three stages: The first flight phase,the upper limb supporting phase and the second flight phase. Time consuming for each stage of the twelve subjects of this experiment are as follows: (0.28±0.02)s,(0.32±0.04)s and (0.14±0.02)s?2. The gravity arm is (0.03±0.01)m and the braking angle is (87.94±0.63)°at the instant touchdown of the palm of the upper limb in the phase of supporting.3. In the phase of upper limb supporting, The peak velocity of the foot in the horizontal direction is(9.62±1.88)m/s and the peak time is (1.25±0.207)s. The Pearson correlation coefficient between the foot and the center of gravity in the direction of horizontal movement is 0.944±0.05, which is highly correlated4.1n phase of the upper limb supporting, the joint angle of the three joints of the shoulder, elbow and wrist is (135.3±7.4)°?(146.1±3.0)°and(104.4±6.8)°at the moment of hand touchdown and (116.1 ±7.6)°?(160.6±3.9)°and(146.7±21.4)°respectively at the moment of hand off the ground. In the whole phase of upper limb supporting , the minimum value of the three joint angles of the shoulder, elbow and wrist is (102.3±5.3)°?(111.8±12.0)°and(94.9±5.0)°The maximum buffer angle of the three joints in the buffer stage is(98.5±7.0)°?(111.8±12.0)°and(102.3±5.3)°.5. In the phase of upper limb supporting, time point from the athlete hand touchdown to the appearance of the vertical reaction force peak value is (0.037±0.009)s and the peak value is (2.81±0.48)BW. The impulse is (9.61±1.97)N/s when the vertical ground reaction force reaches the peak value.6. In the phase of upper limb supporting, the maximum load rate is (381.96±103.93)BW/s and its emerging time is (0.025±0.004)s. Maximum load decay rate is(-337.64±117.81)BW/s and its emerging time is(0.041±0.006)s.7. In the phase of upper limb supportingback handspring movements, the IEMG value of the upper part of trapezius muscle is (0.35±0.09)mv·s, the IEMG value of the deltoid is (0.2±0.05)mv·s, the IEMG value of triceps is (0.2410.05)mv·s, the IEMG value of the extensor muscles of the wrist(0.2±0.05)mv·s and the IEMG value of wrist flexors is (0.49±0.15)mv·s.Conclusion:1. At the moment of hand touchdown~the length of gravity arm is (0.03±0.01)m and the braking angle is(87.94±0.63)°,which is beneficial for the athletes to keep the movement speed and reduce the power loss in the horizontal direction.2. In the phase of upper limb supporting, there is a high correlation between the velocity of foot and the center of gravity in the horizontal direction (correlation coefficient: 0.987), and to increase the speed of the lower limb can increase the speed of movement of the body in the direction of movement.3. In the largest buffer position of upper limbs, as projection of the elbow in the direction of the X axis ishigherthan wrist joint ( 0.04±0.003 ) m,consequently the wrist jointisin a state of passive adduction, articular cartilage is squeezed, in the long term it may cause wrist injury.4. In the upper extremity support phase, when the vertical ground reactionforce comes toits peak, human body needs to bear (2.81±0.48) times of the body weight.And when the vertical ground reaction force increases and reached its peak, shoulder,elbow, wrist-three small articular angle is becoming smaller and smaller and flexor muscle, the triceps muscles, deltoid muscle anterior muscles are elongated and are in a state of eccentric contraction.5.In the phase of upper limb supporting, maximum load attenuation rate and shoulder, elbow joint angular acceleration maxima almost occurred simultaneously,which meansin this stage,the decrease ofshoulder andelbow joint anglecan effectivelyreduce the ground support reaction.6.In the phase of upper limb supporting, the total amount of wrist flexordischarge is the highest, which is related to the frequently stretched eccentric contraction manner of working and the higher activity intensity in the stage off the ground bracing. |
PDF Full Text Request