我国部分优秀男子标枪运动员“交叉步”技术若干速度指标的运动学分析

运用高速摄影拍摄及解析方法对全国大奖赛男子标枪比赛前8名运动员“交叉步”技术中有关速度特征的运动学进行分析,旨在诊断中国男子标枪运动员的技术现状及存在的问题,指导和改进中国男子标枪的技术训练,为加强教学、训练的科学化程度提供参考依据。     

Kinematic analysis of the drag flick in field hockey

Attaining high speed of the stick head and consequently of the ball is essential for successful performance of the drag flick in field hockey, but the coordination pattern used to maximise stick head speed is unknown. The kinematics of the drag flick was studied in ten elite hockey players who performed twenty shots each towards a target located 1.5 m high. A 150 Hz active marker motion analysis system was used, alongside two force plates to detect foot touchdown. Angular velocity and contribution to stick endpoint speed of upper body joints were analysed. Repeated measures ANOVA was used to compare timing of onset and peak angular velocities between joints. Participants used a kinematic pattern that was close to a proximal-to-distal sequence. Trunk axial rotation and lateral rotation towards the target, right wrist flexion and left wrist extension were the main contributors to stick endpoint speed. Coaches should emphasise trunk rotations and wrist flexion and extension movements for maximising stick head speed. Given the high level of the participants in this study, the coordination of joints motions, as reported here, can serve as a guideline for drag flick training.     

Specific tackling situations affect the biomechanical demands experienced by rugby union players

Tackling in Rugby Union is an open skill which can involve high-speed collisions and is the match event associated with the greatest proportion of injuries. This study aimed to analyse the biomechanics of rugby tackling under three conditions: from a stationary position, with dominant and non-dominant shoulder, and moving forward, with dominant shoulder. A specially devised contact simulator, a 50-kg punch bag instrumented with pressure sensors, was translated towards the tackler (n = 15) to evaluate the effect of laterality and tackling approach on the external loads absorbed by the tackler, on head and trunk motion, and on trunk muscle activities. Peak impact force was substantially higher in the stationary dominant (2.84 ± 0.74 kN) than in the stationary non-dominant condition (2.44 ± 0.64 kN), but lower than in the moving condition (3.40 ± 0.86 kN). Muscle activation started on average 300 ms before impact, with higher activation for impact-side trapezius and non-impact-side erector spinae and gluteus maximus muscles. Players’ technique for non-dominant-side tackles was less compliant with current coaching recommendations in terms of cervical motion (more neck flexion and lateral bending in the stationary non-dominant condition) and players could benefit from specific coaching focus on non-dominant-side tackles.     

竞技健美操难度动作C289不同技术特征的运动学分析

摘要：竞技健美操成套动作中高难度动作的完成质量是决定比赛胜负的关键。C289作为具备高、难、险技术特征的难度动作,是运动员比赛中获得高分和竞争奖牌的重要因素,在近年的世界大赛中备受青睐,因此如何提升动作质量,避免扣分点,成为当前亟需解决的训练难题。世界优秀运动员的技术模式是极具价值的模型,本研究运用QUALISYS红外光点高速运动捕捉系统,对2名男子世界冠军完成竞技健美操难度动作C289的不同技术特征进行运动学分析,深入研究其动作原理和关键技术,为难度动作的训练提供参考借鉴,有效促进难度动作的价值提升和创新发展。研究表明：1）2名运动员技术要点不同,起跳阶段麻东髋关节缓冲角度与蹬离速度均大于胡邦达,弹性势能储备更多,蹬离地面收腿,易完成转体与屈体动作,但规范性欠缺。2）胡邦达近乎垂直起跳,转体360°后屈髋的风险性更强,腾空时间较麻东少0.05s,动作清晰流畅;屈体时刻2种技术髋关节角度均小于60°,但麻东后仰幅度大,空中屈体形态位置不标准。3）麻东落地点前后与左右方向重心位移变化较大,胡邦达落地相对准确,可控性较强,其腾空上升阶段垂直方向变化较大4）先转体后屈髋技术难度较大,其动作形式特点更符合规则发展导向。     

线性流形上次反对称矩阵的次特征值的反问题

讨论了线性流形上次反对称矩阵的次特征值的反问题,给出了解存在的条件,并给出了解的通式。本文充分利用了次单位矩阵的作用,将次反对称矩阵的次特征值的反问题转为反对称矩阵的逆特征值问题来解决。     

对我国女排优秀“自由人”李颖接上手飘球技术的运动学分析

＂自由人＂又称＂自由防守队员＂,是国际排联为进一步鼓励防守,促进排球比赛的攻守平衡,使比赛更加激烈精彩,提高其观赏性,而于1999年正式实行的新规则。本文主要采用标准的三维摄像DLT法和录像解析法,对2001-2002年全国女排联赛期间,辽宁女排主场决赛期间的八一队＂自由人＂李颖（原国家队＂自由人＂）和天津队＂自由人＂张娜（国家队＂自由人＂）及天津队的李珊（国家队队员）、杨洁接上手发飘球技术进行运动学研究,旨在提示该过程中蕴含的运动学规律,从而为教练员和运动员的训练和比赛提供理论参考依据。     

Lower extremity power during the squat jump with various barbell loads

The purpose of this study was twofold: (1) to determine the barbell load that maximised the system power as well as the ankle, knee, and hip joint powers during the squat jump, and (2) to compare the system powers computed from two different methods: the centre of mass (COM) method and the barbell method. Seven male throwers were recruited in this study. The system power (COM method) and the ankle, knee, and hip joint powers were determined with the load incrementally set at 0%, 10%, 30%, 50%, 70%, and 90% of one repetition maximum. The largest system power was observed at the load of 30% (p < 0.008) while the largest ankle and knee powers were observed at 70% and 0% (p < 0.05). The barbell method overestimated the system power (p < 0.001) when compared to the COM method. It was concluded that the barbell method could influence load optimisation in squat jump. The optimal barbell load which maximised the system power did not maximise the ankle, knee, or hip power simultaneously.     

Comparison of support leg kinetics between side-step and cross-step cutting techniques

The purpose of this study was to investigate differences in the support leg joint moment and moment power between side-step (SS) and cross-step (CS) cutting techniques with a prescribed 90° cutting angle. Ground reaction forces (1,000 Hz) and three-dimensional kinematics (250 Hz) of SS and CS cutting techniques were collected from 20 male college athletes. Normalised peak knee extension moment was larger in the SS technique than in the CS technique (0.40 ± 0.10 in SS; 0.26 ± 0.08 in CS). In the SS technique, the knee extensors ( ? 0.10 ± 0.06 in SS; ? 0.02 ± 0.04 in CS) and ankle plantarflexors ( ? 0.12 ± 0.05 in SS; ? 0.07 ± 0.03 in CS) did significantly more negative work (normalised). The direction change angle (40.5 ± 8.7° in SS; 33.0 ± 6.8° in CS) and the decrease in horizontal velocity of the centre of mass ( ? 0.63 ± 0.23 m/s in SS; ? 0.31 ± 0.23 m/s in CS) were significantly larger in the SS technique. These results suggest that the SS technique is an effective means of changing running direction at the expense of velocity of the centre of mass and that the CS technique is better for minimising the reduction in horizontal velocity of the centre of mass.     

Influence of sex and limb dominance on lower extremity joint mechanics during unilateral land-and-cut manoeuvres

Limb dominance theory suggests that females tend to be more one-leg dominant and exhibit greater kinematic and kinetic leg asymmetries than their male counterparts, contributing to the increased risk of anterior cruciate ligament injury among female athletes. Thus, the purpose of this study was to examine the influences of sex and limb dominance on lower extremity joint mechanics during unilateral land-and-cut manoeuvres. Twenty-one women and 21 men completed land-and-cut manoeuvres on their dominant limb as well as their nondominant limb. Three-dimensional kinematics and kinetics were calculated bilaterally for the entire stance phase of the manoeuvre. Women performed land-and-cut manoeuvres with altered hip motions and loads as well as greater knee abduction at touchdown compared to men. Dominant limb land-and-cut manoeuvres where characterised by decreased hip flexion at touchdown as well as decreased hip flexion and adduction range of motion compared to nondominant land-and-cuts regardless of sex. The observed sex differences are consistent with previous research regarding mechanisms underlying the sex disparity in anterior cruciate ligament injury rates. However, observed differences regarding limb dominances appear somewhat arbitrary and did not suggest that the dominant or nondominant limb would be at increased risk of anterior cruciate ligament injury.     

Increasing hip and knee flexion during a drop-jump task reduces tibiofemoral shear and compressive forces: implications for ACL injury prevention training

Although most ACL injury prevention programmes encourage greater hip and knee flexion during landing, it remains unknown how this technique influences tibiofemoral joint forces. We examined whether a landing strategy utilising greater hip and knee flexion decreases tibiofemoral anterior shear and compression. Twelve healthy women (25.9 ± 3.5 years) performed a drop-jump task before and after a training session (10–15 min) that emphasised greater hip and knee flexion. Peak tibiofemoral anterior shear and compressive forces were calculated using an electromyography (EMG)-driven knee model that incorporated joint kinematics, EMG and participant-specific muscle volumes and patella tendon orientation measured using magnetic resonance imaging (MRI). Participants demonstrated a decrease in peak anterior tibial shear forces (11.1 ± 3.3 vs. 9.6 ± 2.7 N · kg^?1; P = 0.008) and peak tibiofemoral compressive forces (68.4 ± 7.6 vs. 62.0 ± 5.5 N · kg^?1; P = 0.015) post-training. The decreased peak anterior tibial shear was accompanied by a decrease in the quadriceps anterior shear force, while the decreased peak compressive force was accompanied by decreased ground reaction force and hamstring forces. Our data provide justification for injury prevention programmes that encourage greater hip and knee flexion during landing to reduce tibiofemoral joint loading.