Effects of muscle-tendon length on joint moment and power during sprint starts   总被引：3，自引：2，他引：1  

Mero A  Kuitunen S  Harland M  Kyröläinen H  Komi PV 《Journal of sports sciences》2006,24(2):165-173

The aim of this study was to examine the effects of muscle-tendon length on joint moment and power during maximal sprint starts. Nine male sprinters performed maximal sprint starts from the blocks that were adjusted either to 40 degrees or 65 degrees to the horizontal. Ground reaction forces were recorded at 833 Hz using a force platform and kinematic data were recorded at 200 Hz with a film camera. Joint moments and powers were analysed using kinematic and kinetic data. Muscle - tendon lengths of the medial gastrocnemius, soleus, vastus medialis, rectus femoris and biceps femoris were calculated from the set position to the end of the first single leg contact. The results indicated that block velocity (the horizontal velocity of centre of mass at the end of the block phase) was greater (P < 0.01) in the 40 degrees than in the 65 degrees block angle condition (3.39 +/- 0.23 vs. 3.30 +/- 0.21 m . s(-1)). Similarly, the initial lengths of the gastrocnemius and soleus of the front leg in the block at the beginning of force production until half way through the block phase were longer (P < 0.001) in the 40 degrees than in the 65 degrees block angle condition. The initial length and the length in the middle of the block phase were also longer in the 40 degrees than in the 65 degrees block angle condition both for both the gastrocnemius (P < 0.01) and soleus (P < 0.01-0.05) of the rear leg. In contrast, the initial lengths of the rectus femoris and vastus medialis of the front leg were longer (P < 0.05) in the 65 degrees than in the 40 degrees block angle condition. All differences gradually disappeared during the later block phase. The peak ankle joint moment (P < 0.01) and power (P < 0.05) during the block phase were greater in the 40 degrees than in the 65 degrees block angle condition for the rear leg. The peak ankle joint moment during the block phase was greater (P < 0.05) in the 40 degrees block angle for the front leg, whereas the peak knee joint moment of the rear leg was greater (P < 0.01) in the 65 degrees block angle condition. The results suggest that the longer initial muscle-tendon lengths of the gastrocnemius and soleus in the block phase at the beginning of force production contribute to the greater peak ankle joint moment and power and consequently the greater block velocity during the sprint start.  相似文献   

The distance-time relationship over a century of running Olympic performances: A limit on the critical speed concept     

Dekerle J  Nesi X  Carter H 《Journal of sports sciences》2006,24(11):1213-1221

We analyse the evolution of the slope (critical speed) and the y-intercept (anaerobic distance capacity) of the linear distance-time relationship over a century of Olympic running performances. The distance-time relationship of each Olympic Games (1920-2004) was plotted using the performances in the 800-, 1500- and 5000-m track events. Values for critical speed and anaerobic distance capacity were determined by linear modelling. Mean performances for the 800, 1500 and 5000 m were 104.9 +/- 1.5 s (1.4%), 217.2 +/- 2.8 s (1.3%) and 808.9 +/- 18.4 s (2.3%), respectively. Critical speed improved during the first three-quarters of the twentieth century to reach a plateau in 1984. This is in accordance with the literature (Peronnet & Thibault, 1989) and suggests that "human aerobic endurance" has improved within the century (+13.4%) and tends to stabilize. Anaerobic distance capacity was highly variable over the century (coefficient of variation = 9.4%) and did not show a linear improvement over the years as has previously been suggested (Peronnet & Thibault, 1989). This could be due to an artefact in the application of the two-parameter model to only three Olympic performances. A limitation to the use of this linear mathematical model to fit physiological data may have been demonstrated.  相似文献   

Test-retest reliability of a survey to measure transport-related physical activity in adults     

Badland H  Schofield G 《Research quarterly for exercise and sport》2006,77(3):386-390

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Immediate effects of the use of modified take-off boards on the take-off motion of the long jump during training     

Koyama H  Muraki Y  Ae M 《Sports biomechanics / International Society of Biomechanics in Sports》2006,5(2):139-153

We investigated the immediate effects of the combined use of inclined and raised flat boards on the take-off motion of the long jump. Eight male long jumpers were videotaped with two high-speed video cameras (250 Hz) set perpendicular to the runway. The athletes jumped with three modified take-off boards: upward-inclined boards of two different inclinations (2.5 and 5.0 degrees), and a raised flat board (50 mm high). The jumpers performed pre- and post-jumps using their own techniques before and after use of the boards to test their effects. The post- jump revealed significantly less reduction in the horizontal velocity during the take-off than the pre-jump, and the effectiveness of converting the velocity from horizontal to vertical increased significantly in the post-jump. The post-jump demonstrated significantly less knee flexion of the take-off leg during take-off. The reduced knee flexion and slower extension velocity of the take-off leg in the second phase of the post-jump contributed to increasing the knee extension torque in the second phase and resulted in the increases in vertical ground reaction force and vertical velocity. These results suggest that the combined use of the inclined and raised flat boards induced immediate effective changes in the kinematics and kinetics of the take-off motion and represent appropriate training tools for take-off techniques of the long jump.  相似文献   

The role of parents in the development of children's ethnic attitudes     

RADKE-YARROW M  TRAGER H  MILLER J 《Child development》1952,23(1):13-53

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我所犯的错误之本質与其原因     

H·K·岡察洛夫  张醒石 《人民教育》1950,(4)

對於我的『敎育學原理』一書的討論已經繼續了三天。討論是在對我作原則性批評的環境中,首先是在自我批評和分析我們敎育科學原理的環境下進行的。我認爲對於我的『敎育學原理』一書的批評是正確的、是布爾什維克的。同志們的批評對我有很大的幫助。我在我的作品出版以前和出版以後會經將它讀過好幾遍。我自己也見到了和知道了我作品中一系列的錯誤與遺漏,但是根據我在這個會上所聽到的,我應該爽直並誠懇地說一說甚至自己没有懷疑過的許多東西.這是顯而易見的。所有髮言的同志們不單是個别地、各自分別地,並且在有敎師們參加的教育學院和師範學院的敎育系中都仔細地分析了我的著作。  相似文献   

The autopsy report on Diderot     

DIECKMANN H 《Isis; an international review devoted to the history of science and its cultural influences》1950,41(125-126):289-290

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信息系统研究中的尺度设计——一个实现一维性评价的范例     

Albert H.Segars  张云军 《中国教育信息化》1995,(2)

由于尺度在评价信息系统产品时具有多方面的作用,因此在信息系统领域,设计和评价用来度量潜在现象的尺度一直是人们感兴趣的话题。一般来说,尺度的度量性质是通过传统技术来评价的,如项与总体相关法(item—to—total correlations),a系数和探索因子法(ex-ploratory factor analysis)。尽管在探索状况下它们很有效,但它们却很少提供有关一维性的评价。一维尺度只度量单一的特征。这一性质是测度论中的一条基本假设,它在精确度量变量间的相关关系中也是相当重要的。这篇论文中主要讲了一个设计一维尺度的范例,这个范例是从市场研究、教育、心理学中的成熟技术得到启发,使用了确认因子分析法(CFA—Con-firmatory Factor Analysis)来评价度量性质。重要的是,CFA对一维性的解释比传统方法更严格,并且在许多情况下对尺度的可接受性会得到不同的结论。  相似文献   

录音机—写作的得力助手     

玛丽·H·克劳夫特  兰湖 《世界文化》1984,(1)

帮助你评改自己的文稿作家常常面对自己的文稿,飘飘然地沉浸在自我陶醉之中。他们自以为自己的文章文笔不凡,不,简直是惊人之作,以至于连一个标点符号都不想改动。其实这种心情在学生们的身上何尝不是如此呢?为了医治这种病态的自我欣赏,我们奉劝那些进行写作的同学,写作时不妨把自己的草稿对着录音机读一遍,录下音来,然后丢开稿子听一听录音。这样做,可以动员听觉来参与文章的评改。效果如何呢?你会发现草稿里那些拗口的语句——不合语法的结构、重复罗唆的词语、含糊不清的文笔转折——种种失着败笔竟一下子钻了出来。然后,谢天谢地,动手修改吧!  相似文献   

Williams & wilkins capitulates     

Bloomquist H 《Bulletin of the Medical Library Association》1973,61(1):58-60

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