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RJ Maughan 《Journal of sports sciences》2013,31(9):883-889
The use of dietary supplements is widespread in sport and most athletes competing at the highest level of competition use some form of dietary supplementation. Many of these supplements confer no performance or health benefit, and some may actually be detrimental to both performance and health when taken in high doses for prolonged periods. Some supplements contain excessive doses of potentially toxic ingredients, while others do not contain significant amounts of the ingredients listed on the label. There is also now evidence that some of the apparently legitimate dietary supplements on sale contain ingredients that are not declared on the label but that are prohibited by the doping regulations of the International Olympic Committee and of the World Anti-Doping Agency. Contaminants that have been identified include a variety of anabolic androgenic steroids (including testosterone and nandrolone as well as the pro-hormones of these compounds), ephedrine and caffeine. This contamination may in most cases be the result of poor manufacturing practice, but there is some evidence of deliberate adulteration of products. The principle of strict liability that applies in sport means that innocent ingestion of prohibited substances is not an acceptable excuse, and athletes testing positive are liable to penalties. Although it is undoubtedly the case that some athletes are guilty of deliberate cheating, some positive tests are likely to be the result of inadvertent ingestion of prohibited substances present in otherwise innocuous dietary supplements. 相似文献
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The purpose of the study was to determine whether multidimensional perceptual-cognitive skills training, including situational awareness, anticipation, and decision making, improves on-court performance in older adults when compared with a physical training program, including stroke and footwork development. Senior tennis players (N = 27) were randomly assigned to one of three groups: perceptual-cognitive skills training, technique-footwork training, or no training. Results indicated that participants receiving perceptual-cognitive skills training had significantly faster response speeds, higher percentage of accurate responses, and higher percentage of performance decision making in posttest match situations. Findings provide clear evidence that perceptual-cognitive skills can be trained in aged individuals. Implications and suggestions for future research are offered. 相似文献
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Fluid and electrolyte balance in elite male football (soccer) players training in a cool environment
There are few data in the published literature on sweat loss and drinking behaviour in athletes training in a cool environment. Sweat loss and fluid intake were measured in 17 first-team members of an elite soccer team training for 90 min in a cool (5°C, 81% relative humidity) environment. Sweat loss was assessed from the change in body mass after correction for the volume of fluid consumed. Sweat electrolyte content was measured from absorbent patches applied at four skin sites. Mean (?± s) sweat loss during training was 1.69?±?0.45 l (range 1.06?-?2.65 l). Mean fluid intake during training was 423?±?215 ml (44?-?951 ml). There was no apparent relationship between the amount of sweat lost and the volume of fluid consumed during training (r 2 = 0.013, P = 0.665). Mean sweat sodium concentration was 42.5?±?13.0 mmol?·?l?1 and mean sweat potassium concentration was 4.2?±?1.0 mmol?·?l?1. Total salt (NaCl) loss during training was 4.3?±?1.8 g. The sweat loss data are similar to those recorded in elite players undergoing a similar training session in warm environments, but the volume of fluid ingested is less. 相似文献
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This contribution considers a variety of aspects of the bloodstock breeding world during the three decades following World War Two, focusing in particular on the breeders of thoroughbred horses and the attitudes of those breeders towards their calling. It is argued that even at this late stage of its history, the persistence of the Corinthian amateur ideal, a dogged indifference to the realities of social and economic change, and a high degree of institutional social exclusiveness was in part responsible for the relative decline of what had been, in the inter-war years, the world's pre-eminent bloodstock industry. 相似文献
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RJ Botha 《Educational studies》2013,39(4):431-443
Studies on school restructuring and the leadership role of the principal in this process suggest that what has been the traditional leadership approach of the principal appears to be changing in relation to the substantial changes and school-wide reforms that are continually taking place in schools today. These school reform initiatives necessitate new and creative ways of thinking about our concept of educational leadership and its various approaches. It also became clear from the literature on leadership that a person’s assumption of various types of knowledge influence his or her leadership approach. The purpose of this study, based on a quantitative empirical study in selected South African schools, is to identify this impact of principals’ assumptions of knowledge on their leadership approaches. A total of 100 questionnaires with open-ended questions were sent electronically to school principals of randomly selected schools to assess the link between principals’ assumptions about the nature of knowledge and principal leadership. The t-test, Lambda test and an Analysis of Variances test were used to analyse the data. The findings confirm the relationship between core epistemological beliefs (EBs) and beliefs about leadership practices among South African school principals and provide substantial justification for using EBs in the study of school leadership. 相似文献
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This paper analyses the market transformation in heritage tourism destinations when excessive tourism demand determines the emergence of a class of excursionists among visitors. Building on the approach of Keane (1997) and Shapiro (1983), some important dimensions of sustainable tourism development are highlighted. The lesser capacity of excursionists to learn the true quality of the tourist goods provides an opportunity for producers to cut back on quality. To serve high quality goods and keep up the reputation of the destination, producers need to gain a mark-up on price that might not be sustained in a competitive market. Hence the decline in ``high-paying' demand segments, increasingly substituted by visitors with lesser quality expectations, has significant consequences on the use and preservation of the heritage. The proposed formulation allows the identification of appropriate policy instruments to reverse this process. 相似文献
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Earlier work on the supply of labour of artists has shown that, whenever workers derive satisfaction from the process of work, which is usually the case for artists, some traditional results are reversed. As their proponents make clear this analysis is essentially static, as it does not take into account the intertemporal dimension of the supply of labour. The paper argues that to provide such a dynamic analysis three routes are available: the human capital approach, the household production approach and the evolutionary approach. The paper, therefore, is aimed at discussing the adequacy of various theoretical approaches to the treatment of a specific question. 相似文献
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