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排序方式: 共有748条查询结果,搜索用时 15 毫秒
111.
Izatus Shima Taib Siti Balkis Budin Seri Maseran Siti Nor Ain Jamaludin Mohamed Santhana Raj Louis Srijit Das Sulaiman Sallehudin Nor Fadilah Rajab Othman Hidayatulfathi 《Journal of Zhejiang University. Science. B》2009,10(11):813-819
Litsea elliptica Blume leaves have been traditionally used as medicinal herbs because of its antimutagenicity, che-mopreventative and insecticidal properties. In this study, the toxic effects of L. elliptica essential oil against Sprague-Dawley rat's red blood cells (RBCs) were evaluated. L. elliptica essential oil was given by oral gavage 5 times per week for 3 treated groups in the doses of 125, 250, and 500 mg/(kg body weight), respectively, and the control group received distilled water. Full blood count, RBC osmotic fragility, RBC morphological changes, and RBC membrane lipid were analyzed 28 d after the treatment. Although L. elliptica essential oil administration had significantly different effects on hemoglobin (Hb), mean cell hemoglobin concentration (MCHC), mean cell volume (MCV), and mean cell hemoglobin (MCH) in the experimental groups as compared to the control group (P<0.05), the values were still within the normal range. L. elliptica induced morphological changes of RBC into the form of echinoeyte. The percentage of echinocyte increased significantly among the treated groups in a dose-response manner (P<0.001). The concentrations of RBC membrane phospholipids and cholesterol of all treated groups were significantly lower than those of control group (P<0.001). However, the RBC membrane osmotic fragility and total proteins of RBC membrane findings did not differ significantly between control and treated groups (P>0.05). It is concluded that structural changes in the RBC membrane due to L. elliptica essential oil administration did not cause severe membrane damage. 相似文献
112.
Greg Atkinson Richard Davison Asker Jeukendrup Louis Passfield 《Journal of sports sciences》2013,31(9):767-787
Abstract In this holistic review of cycling science, the objectives are: (1) to identify the various human and environmental factors that influence cycling power output and velocity; (2) to discuss, with the aid of a schematic model, the often complex interrelationships between these factors; and (3) to suggest future directions for research to help clarify how cycling performance can be optimized, given different race disciplines, environments and riders. Most successful cyclists, irrespective of the race discipline, have a high maximal aerobic power output measured from an incremental test, and an ability to work at relatively high power outputs for long periods. The relationship between these characteristics and inherent physiological factors such as muscle capilliarization and muscle fibre type is complicated by inter-individual differences in selecting cadence for different race conditions. More research is needed on high-class professional riders, since they probably represent the pinnacle of natural selection for, and physiological adaptation to, endurance exercise. Recent advances in mathematical modelling and bicycle-mounted strain gauges, which can measure power directly in races, are starting to help unravel the interrelationships between the various resistive forces on the bicycle (e.g. air and rolling resistance, gravity). Interventions on rider position to optimize aerodynamics should also consider the impact on power output of the rider. All-terrain bicycle (ATB) racing is a neglected discipline in terms of the characterization of power outputs in race conditions and the modelling of the effects of the different design of bicycle frame and components on the magnitude of resistive forces. A direct application of mathematical models of cycling velocity has been in identifying optimal pacing strategies for different race conditions. Such data should, nevertheless, be considered alongside physiological optimization of power output in a race. An even distribution of power output is both physiologically and biophysically optimal for longer ( >4km) time-trials held in conditions of unvarying wind and gradient. For shorter races (e.g. a 1km time-trial), an‘all out’ effort from the start is advised to‘save’ time during the initial phase that contributes most to total race time and to optimize the contribution of kinetic energy to race velocity. From a biophysical standpoint, the optimum pacing strategy for road time-trials may involve increasing power in headwinds and uphill sections and decreasing power in tailwinds and when travelling downhill. More research, using models and direct power measurement, is needed to elucidate fully how much such a pacing strategy might save time in a real race and how much a variable power output can be tolerated by a rider. The cyclist's diet is a multifactorial issue in itself and many researchers have tried to examine aspects of cycling nutrition (e.g. timing, amount, composition) in isolation. Only recently have researchers attempted to analyse interrelationships between dietary factors (e.g. the link between pre-race and in-race dietary effects on performance). The thermal environment is a mediating factor in choice of diet, since there may be competing interests of replacing lost fluid and depleted glycogen during and after a race. Given the prevalence of stage racing in professional cycling, more research into the influence of nutrition on repeated bouts of exercise performance and training is required. 相似文献
113.
Xiaofen Deng Keating Louis Harrison Jr. Brian Dauenhauer Li Chen Jianmin Guan 《Research quarterly for exercise and sport》2013,84(4):747-755
The purpose of the study was to examine Hispanic and other minority ninth-grade students' health-related fitness (HRF) knowledge, using FitSmart, a standardized test for high school students. The test consisted of 50 weighted multiple choice items, measuring six subcontent components. Means and standard deviations of the overall scores and the subcontent scores were computed. The findings suggested that students demonstrated mastery of one subcontent component but failed to meet passing values for all other subcontents and overall HRF knowledge. Female students outscored their male counterparts, but there was no difference for ethnicity. More efforts are needed to ensure that Hispanic and other minority high school students master fundamental HRF knowledge. 相似文献
114.
Abstract The purpose of this study was to assess the potential influence of birth quarter on the frequency of physical activity and participation in specific activities during adulthood. We used data from one national and one provincial survey, the 2005 Canadian Community Health Survey and the 1998 Quebec Social and Health Survey (Enquête sociale et de santé du Québec) respectively. We analysed the distribution of participants at each level of practice of a given leisure activity and work-related physical activity. In the Canadian Community Health Survey, a relative age effect was found for participation in soccer in the 25- to 60-year-old population. However, for volleyball, a significant relative age effect was also observed but with over-representation of the last quarters of the year for the whole population and for men aged 12–60 years. In the Quebec Social and Health Survey, significant differences in the frequency of distribution without a relative age effect were revealed for participation in women's ice hockey, work-related physical activity level, and stage of change for physical activity. Overall, the data indicate that the systematic relative age effect reported in other studies for some competitive sports, such as ice hockey and soccer, is not as prevalent in leisure physical activities during adulthood. This may reflect lower competitive selection and attrition in population physical activity compared with competitive sports in younger athletes. 相似文献
115.
Jordan Santos-Concejero Ross Tucker Cristina Granados Jon Irazusta Iraia Bidaurrazaga-Letona Jon Zabala-Lili 《Journal of sports sciences》2013,31(9):853-859
AbstractThis study investigated the influence of the regression model and initial intensity during an incremental test on the relationship between the lactate threshold estimated by the maximal-deviation method and performance in elite-standard runners. Twenty-three well-trained runners completed a discontinuous incremental running test on a treadmill. Speed started at 9 km · h?1 and increased by 1.5 km · h?1 every 4 min until exhaustion, with a minute of recovery for blood collection. Lactate–speed data were fitted by exponential and polynomial models. The lactate threshold was determined for both models, using all the co-ordinates, excluding the first and excluding the first and second points. The exponential lactate threshold was greater than the polynomial equivalent in any co-ordinate condition (P < 0.001). For both models, the lactate threshold was lower when all co-ordinates were used than when the first and the first and second points were excluded (P < 0.001). 10-km race pace was correlated with both the exponential and polynomial lactate thresholds for all the co-ordinate conditions (r ≥ 0.75, P < 0.001 and r ≥ 0.56, P < 0.05, respectively). The results suggest that the exponential lactate threshold should be used instead of the polynomial equivalent since it is more strongly associated with performance and is independent of the initial intensity of the test. 相似文献
116.
Joe W. Burden Jr. Louis Harrison Jr. Samuel R. Hodge 《Research quarterly for exercise and sport》2013,84(2):224-237
The purpose of this study was to examine the perceptions of African American faculty on their organizational socialization in kinesiology-based (i.e., sport pedagogy, exercise physiology, motor behavior, sport management/history) programs at predominantly White American1 institutions of higher education (PW-IHE). Participants were 9 African American tenure-track faculty members from various kinesiology-based programs at PW-IHE. Data were gathered via interviewing and analyzed within the framework of critical race theory (Ladson-Billings, 2000). Findings are presented using storytelling and thematic narratives. Interviews with the participants revealed four major recurring themes with regard to: (a) resources, opportunities, and power structures; (b) programmatic neglects and faculty mentoring needs; (c) social isolation, disengagement, and intellectual inferiority issues; and (d) double standards, marginalization, and scholarship biases. This study suggests that faculty and administrators at PW-IHE should develop sensitivity toward organizational socialization issues relevant to faculty of color. 相似文献
117.
118.
Boy Trouble: Rhetorical framing of boys' underachievement 总被引:1,自引:1,他引:1
Jordan J. Titus 《Discourse: Studies in the Cultural Politics of Education》2004,25(2):145-169
This article examines discourse in the United States used to socially construct an “underachieving boys” moral panic. Employing discourse analysis I examine the adversarial rhetoric of claims-makers and the frames they deploy to undermine alternative and conflicting accounts (of females as disadvantaged) and to forestall any challenges to the scientific authority of their own (biological essentialist) account of crisis. I illustrate how this discourse adapts the rhetorical frame of gender equity from the discourse it politically opposes, and uses it to legitimate its own goals. I find that the framing of innocent victimized boys as scientific “truth” is aligned with a broader masculinity politics that blames certain “folk devils”, and a synchronic moral panic about fearsome (black) male youth. I conclude by considering the success of this moral panic as evidenced by changes in educational policies and practices in the United States. 相似文献
119.
Louis Burgos 《European Journal of Psychology of Education - EJPE》2003,18(2):135-155
Our goal is to study the effects of early paternal involvement on a child’s socialization. Usually in works concerning the
question, we study the father’s contribution with questionnaires, we base our evaluation of involvement on the behavior declared
by the subject. We have attempted to analyze the affective dimension of this involvement. We have developed a model of the
father-child relationship which articulates the affective investment with the father’s functions (mediation and sanction).
Starting with this model, we analyzed the contents of ten nondirective interviews, then we ranked these ten fathers according
to their relationship with their children.
We have studied early socialization with the concept of mimesis, more pertinent than that of interaction. The social behavior
of ten children was observed in a nursery school class during a period of free time. Their conduct was placed into two categories:
behavior directed towards the peer or behavior directed towards conformity to the pupil’s social role. 相似文献
120.
Teachers’ capacity for organizational learning: the effects of school culture and context 总被引:1,自引:0,他引:1
This paper investigates how key elements of school culture are associated with teachers’ capacity to find and act on new information. We analyzed survey data from 3,579 teachers located in 117 schools which were a randomly selected sample from 9 states in the US. We found that school cultural components such as academic press, student support, and trust and respect among teachers promote teachers’ capacity for organizational learning. We also found that the role of teacher professional culture in molding the capacity for organizational learning is critical. In terms of school contexts, we identified that school level (elementary, middle, and high school) was associated with teachers’ capacity for organizational learning in 2 different ways. First, as the school level increases, the capacity for organizational learning tends to decrease. Second, as school level increases, the positive relation between reflective dialogue and teachers’ capacity for organizational learning is weakened. Implications of these results are discussed. 相似文献