The physiological cost of velocity coupling during tennis groundstrokes     

Cooke K  Davey PR 《Journal of sports sciences》2007,25(7):815-821

Velocity coupling denotes a perceptual motor behaviour known to occur during coincidence timing tasks. Individuals have been shown to increase their effector limb speed with increases in stimulus speed during interceptive tasks. However, little is known about the physiological effects of velocity coupling. The aim of this study was to determine the physiological cost of velocity coupling during tennis groundstrokes. Eight male and eight female competitive tennis players volunteered to perform three 4-min bouts of continuous groundstrokes against balls projected from a tennis ball machine at speeds of 18, 22, and 27 m x s(-1) (65, 79, and 97 km x h(-1)) and a frequency of 14 balls per minute, the order of which was counterbalanced. Breath-by-breath pulmonary gas exchange, heart rate, locomotion time, and limb acceleration were measured throughout each of the 4-min bouts. Capillary blood samples (for blood lactate analysis), rating of perceived exertion, and difficulty rating were taken at the end of each bout. Increasing ball speed did not influence the locomotion time between groundstrokes but did result in a bilateral increase in both the mean upper- and lower-limb acceleration (all P < 0.05). Velocity coupling behaviour increased oxygen uptake, blood lactate concentration, heart rate, rating of perceived exertion, and perceived task difficulty (all P < 0.05). It would appear, therefore, that velocity coupling influenced tennis groundstroke behaviour and indirectly modified the concurrent cardiopulmonary and metabolic responses.  相似文献   

How persistent and general is the contextual interference effect?     

Russell DM  Newell KM 《Research quarterly for exercise and sport》2007,78(4):318-327

The persistence and generality of the contextual interference (CI) effect was tested using a rapid sequential aiming task. Participants (N=48) practiced three movement patterns for three blocks of 18 trials under a blocked (BL) or random (RA) schedule. Movement patterns were displayed and KR provided throughout practice and testing. A 24-hr delayed knowledge of results (KR) retention test included three blocks of 18 trials, followed by a transfer test of a single new movement pattern. In contradiction of the CI effect, RA practice provided an advantage for RA retention only, not BL retention. Furthermore, group differences at transfer were not persistent. Hence, RA practice does not necessarily provide enhanced, context-free learning, but it is essential training for task switching. Overall the findings reveal limited persistence and generality of the CI effect.  相似文献   

Classroom Life     

Karl Miller 《Changing English: An International Journal of English Teaching》2014,21(2):117-121

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Knowledge: Its creation, distribution, and economic significance, vol. II. The branches of learning : Fritz Machlup. Princeton, NJ: Princeton University Press, 1982. pp. xii + 205. $19.00 (cloth)     

Karl A. Fox 《Economics of Education Review》1985,4(4):351-352

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Beyond the Present State of Affairs: Bildung and the Search for Orientation in Rapidly Transforming Societies     

Helmut Peukert 《Journal of Philosophy of Education》2002,36(3):421-435

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ON THE FUNCTIONS,RESPONSIBILITIES AND FUTURE WORK OF THE NATIONAL EQUIVALENCE COMMISSION OF THE GERMAN DEMOCRATIC REPUBLIC     

Karl Lojewski 《Higher Education in Europe》1985,10(2):122-125

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Planning a public presentation     

Karl L. Kaufmann 《TechTrends》1987,32(6):20-23

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Information and opposition in Austrian nuclear energy policy     

Helmut Hirsch  Helga Nowotny 《Minerva》1977,15(3-4):316-334

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Some aspects of children's ability to solve mathematical problems     

Adolf Afekenstam  Karl Greger 《Educational Studies in Mathematics》1983,14(4):369-384

This survey presents the essentials of a study concerning problem solving ability in children aged 12–13. It forms part of a large project concerning the impact of calculators and computers in school mathematics and the consequences for certain basic abilities. The contents of the survey are in brief:

? definition of problem solving ability;

? test construction;

? interviews;

? supplementary investigations.

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As Time Goes By: Children''s Early Understanding of Growth in Animals   总被引：6，自引：0，他引：6  

Karl S. Rosengren  Susan A. Gelman  Charles W. Kalish  Michael McCormick 《Child development》1991,62(6):1302-1320

Beliefs about naturally occurring transformations were examined in children aged 3 to 6 years in 4 experiments. Experiment 1 tested children's understanding that animals (but not artifacts) predictably get larger over time. Experiment 1a examined whether the results obtained in the first experiment could be attributed to an added memory component on the artifact task. Experiment 2 further examined beliefs about the aging of artifacts. In Experiment 3, color and shape (metamorphosis) changes of animals were investigated. At all ages, children appeared to understand that animals get larger and not smaller with age. While older children and adults allowed for rather dramatic changes in the size and shape of animals over the life span if the alternative involved decreasing in size with age, preschool children were less willing to accept these changes. Taken together, the results of these studies suggest that even young preschool children have 2 conceptual insights about natural transformations: that they are lawful and nonrandom, and that they are domain and mechanism specific. Further, children as young as age 3 are able to go beyond the perceptual appearance of animals in making judgments about transformations caused by growth. Implications for children's understanding of personal and species identity are discussed.  相似文献