摘要：随着美国学校对学生学习成绩的关注日益提升,学生从事体育锻炼的机会日趋减少。为证明减少体育锻炼可能影响学习成绩,近50年以来,科研人员一直在探究体育锻炼对青少年的认知与学习成绩的影响。本文从历史的角度,对比分析近5年和5年前所发表的体育锻炼及学习成绩相关研究成果。共有125篇论文被纳入研究范围,其中近5年发表的论文有53篇。分析发现:近年来的整体研究质量有所提高,但研究结果仍然不一致:许多使用横断面研究设计,但研究方法大相径庭;大部分研究的结论表明体育锻炼对学习成绩有正面影响。今后的研究应通过完善的研究设计,确定可以有效提升学习成绩的体育锻炼项目及运动量。

摘要：Certain dietary, physical activity, and sedentary behaviors have been studied extensively and consistently have been found to be associated with childhood overweight and obesity Productive sedentary-to-light activity pursuits may enhance the relationship among positive health behaviors. The purpose of this study was to identify the prevalence of overweight and obesity in a population of adolescents participating in a creative, problem-solving afterschool program and to identify the physical activity, sedentary, and dietary behaviors related to overweight and obesity in this group. This study describes health behaviors thought to be related to weight status for 1679 adolescents in grades 6 12 participating in a competitive, creative, team-oriented, problem-solving afterschool program. Self-reported dietary, physical activity, and sedentary behavior data were collected in this convenience sample based on the 2007 Youth Risk Behavior Survey. Measured height and weight data were collected to calculate BMI percentile. Using multinomial regression, models were constructed to predict the likelihood of being classified as overweight/obese. The prevalence of overweight in the study population was 15.6%, obese was 11.4%. Fruit/vegetable intake, milk consumption, moderate-to-vigorous physical activity, television time, and total screen time were all independently associated with weight status. After controlling for all covariates, male gender, minority racial/ethnic status, and high screen time while not meeting the physical activity recommendation significantly increased the likelihood of overweight/obesity. The participants in the current study are leaner and engage in healthier behaviors compared to national data for adolescents. The interactive variable combining both sedentary and PA measures is a relatively new technique used to provide a better understanding of the relationship between sedentary and physical activity behaviors as they relate to weight status. Even among

摘要：Background: Smokeless tobacco is widely used by athletes to enhance performance. Nicotine is a central nervous system stimulant and acts on cardiocirculatory and metabolic systems, involving tissue blood flow and circulatory vasoreactivity. The aim of this study was to investigate the effects of the oral smokeless tobacco(Swedish snus(SS)) on the perception of fatigue and time to exhaustion(TTE) during moderate-intensity aerobic ***: Fourteen healthy non-tobacco male users were recruited for a double-blind, controlled crossover design(SS vs. snus placebo(SP)).Subjects were tested for 3 sessions: experimental session 1(Exp1) consisted of an incremental test to determine the maximal aerobic power output(Wmax), whereas Exp2 and Exp3 consisted of exercising at 65%Wmaxuntil exhaustion in SS or SP conditions. During Exp2 and Exp3, muscle and cerebral oxygenation was assessed by means of near-infrared spectroscopy, and the rating of perceived exertion(RPE) was ***: Comparing SS with SP tests, significant differences(p < 0.05) were found in the values of cerebral(～3%) and muscular tissues oxygenation(～4%) in the first 30 min of exercise. The RPE values were not significantly different between the 2 conditions(SS vs. SP). No significant difference was found in TTE(SS: 54.25 § 21.84 min; SP: 50.01 § 17.03 min).Conclusion: This study showed that muscular and cerebral oxygenation increased significantly with snus administration during an endurance exercise until exhaustion, but this did not affect fatigue perception and TTE. The results showed that snus could not be considered an ergogenic substance in non-tobacco users.