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951.
C.A. Seley 《Journal of The Franklin Institute》1910,169(4):278-295
It has been the custom among designers of freight cars either with underframes of steel or of wood to depend upon the strength of the underframe alone in making computations for a specified carrying capacity, despite the fact that the superstructure in many cases can and does constitute a truss. The author presents the evolution in design of structural steel freight cars, with which he has been closely identified, where the value of the superstructure as a tress has been duly considered as an element of strength and in reducing weight. 相似文献
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Two mechanisms have been suggested to explain stretching-induced maximum force depression: a mechanical alteration in the stretched muscle and an impairment of neural activation. Electrical stimulation allows standardization of the level of muscle activation without being limited by neural control. The aim of this study was to evaluate the stretching-induced changes in the electrical and mechanical properties of muscle during electrically elicited contractions. Twelve participants (age 22 +/- 1 years; body mass 75 +/- 2 kg; stature 1.79 +/- 0.02 m; mean +/- standard error) underwent six electrical stimulations of the medial gastrocnemius muscle before and after stretching. During the contractions, surface electromyogram (EMG) and mechanomyogram (MMG) were recorded simultaneously together with force. After stretching we found: (i) no differences in EMG parameters; (ii) MMG amplitude decreased by 4 +/- 1% (P < 0.05); and (iii) the peak force, the peak rate of force development, and the acceleration peak of force development decreased by 12 +/- 3%, 14 +/- 1%, and 24 +/- 5%, respectively (P < 0.05). In conclusion, acute passive stretching did not change EMG properties but altered the mechanical characteristics of the contracting muscle. Indeed, muscle force-generating capacity and stiffness of the muscle-tendon unit were significantly impaired. 相似文献
954.
Stressors in elite sport: a coach perspective 总被引:1,自引:1,他引:0
We examined the varying performance and organizational stressors experienced by coaches who operate with elite athletes. Following interviews with eleven coaches, content analysis of the data revealed coaches to experience comparable numbers of performance and organizational stressors. Performance stressors were divided between their own performance and that of their athletes, while organizational stressors included environmental, leadership, personal, and team factors. The findings provide evidence that coaches experience a variety of stressors that adds weight to the argument that they should be labelled as "performers" in their own right. A variety of future research topics and applied issues are also discussed. 相似文献
955.
Sharp NC 《Journal of sports sciences》2008,26(11):1127-1133
Since Hugh Montgomery discovered the first of what are now nearly 200 "fitness genes", together with rapid advances in human gene therapy, there is now a real prospect of the use of genes, genetic elements, and/or cells that have the capacity to enhance athletic performance (to paraphrase the World Anti-Doping Agency's definition of gene doping). This overview covers the main areas of interface between genetics and sport, attempts to provide a context against which gene doping may be viewed, and suggests a futuristic legitimate use of genomic (and possibly epigenetic) information in sport. 相似文献
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Vlachopoulos SP Kaperoni M Moustaka FC Anderson DF 《Research quarterly for exercise and sport》2008,79(3):283-299
The present study reported on translating the Exercise Identity Scale (EIS: Anderson & Cychosz, 1994) into Greek and examining its psychometric properties and cross-cultural validity based on U.S. individuals' EIS responses. Using four samples comprising 33, 103, and 647 Greek individuals, including exercisers and nonexercisers, and a similar sample comprising 800 U.S. individuals, the concurrent validity, factor structure, internal reliability, test-retest reliability, external validity, gender invariance, and cross-cultural validity of the EIS responses were examined using confirmatory factor analytical procedures. The results supported the concurrent validity, an adequate unidimensional factor structure for the translated EIS and the internal reliability and test-retest reliability over a 6-week interval. Further, cross-gender configural, partial metric, partial strong factorial, and partial strict factorial invariance and cross-cultural configural and partial metric invariance supported the cross-cultural equivalence of the EIS versions. Moreover, the external validity of the translated EIS responses was also supported. Overall, the findings supported the validity of the exercise identity construct outside North American boundaries and the EIS items' equivalence, providing initial evidence for its cross-cultural applicability. 相似文献