微博实名制及其推进社会诚信的作用

微博已经成为中国人交朋结友和发表意见的重要平台,同时也存在谣言泛滥等诸多负面现象。2011年底到2012年初,微博实名制在北京市开始全面推行,采取了"后台实名、前台自愿"的方式。微博实名制的采取,对于规范社交网络上机构和个人的言论,增强社会诚信,具有一定的积极意义。     

施斗姆定理证明的探讨

介绍了施斗姆定理的一种证明方法,通过这种证明使我们更易理解施斗姆定理的含义,掌握施斗姆定理,从而达到运用施斗姆定理讨论多项式实数根的目的．     

Position statement: Testing physical condition in a population – how good are the methods?

Abstract

A poor physical condition – expressed as physical inactivity and poor physical fitness – is associated with the development of chronic diseases and premature death. Our aim was to evaluate the methods currently available for measuring physical activity and physical fitness in the general population.

Physical activity is determined by duration, frequency, and intensity and derives from many different domains, making it difficult to assess over long periods and no feasible general criterion measure exists. Both objective and subjective methods are available. Of the objective methods, accelerometry is the most attractive technology, and is well enough developed for general use in large populations. The advantage of accelerometry is that it is not dependent on the memory of the individual, but its main disadvantage is that it grossly underestimates energy expenditure, due to the lack of registration of certain activities. This may be overcome to a certain extent by combining accelerometry with heart rate monitoring, although this still does not measure activity in different domains. Of the subjective methods, self-report questionnaires are inexpensive and easy to administer. Many questionnaires have been developed, but we require (1) consensus on which measures to use for validation and (2) further development of internationally standardized questionnaires for use in different settings and to address different scientific questions. Many questionnaires correlate well with biological markers and development of chronic diseases, but subjective measurement will always entail a certain degree of misclassification. Furthermore, unstructured physical activity such as housework and gardening may be subject to recall bias. No method appears better to any other, and the choice of instrument will depend on the research question being asked. Future research should combine information from both objective and subjective methods.

Physical fitness comprises several components, including cardiorespiratory endurance and muscle strength and endurance. Direct measurement of oxygen consumption is the criterion measure for cardiorespiratory endurance. As regards muscle strength and endurance, only test–retest reliability is available. Hand-held dynamometers greatly facilitate field testing for maximal isometric muscle strength assessment, while force plate measurements can be used for the lower extremities. For endurance, simple tests such as push-ups and sit-ups are reliable.     

Social influence in relation to current and intended physical activity among adolescents

Abstract

The aim of the present study was to examine the impact of social support and negative social influence from various contexts on adolescents’ current and intended physical activity. Questionnaire data were obtained from 1156 students aged 16–17 years. Relationships among variables were examined with principal component analysis and structural equation modelling. Social influence from several contexts was strongly related to current and intended physical activity, particularly among students in work preparing school programmes. Social support in a sport club context provided the strongest unique contribution to the relationship with physical activity, and social support from an outside perspective (e.g. suggestions, help to plan, and positive talk about physical activity), from the contexts school and leisure, had multidimensional effects. Social support could exist in tandem with experiences of negative social influences (e.g. complaints, critique, teasing). In conclusion, it is necessary to expand our understanding of processes that surround supportive as well as negative social influences on adolescents’ level of physical activity and distinguish between main, buffering, and intervening effects of social support.     

High Body Mass Index is not a barrier to physical activity: Analysis of international rugby players’ anthropometric data

Abstract

Recent data indicate that levels of overweight and obesity are increasing at an alarming rate throughout the world. At a population level (and commonly to assess individual health risk), the prevalence of overweight and obesity is calculated using cut-offs of the Body Mass Index (BMI) derived from height and weight. Similarly, the BMI is also used to classify individuals and to provide a notional indication of potential health risk.

It is likely that epidemiologic surveys that are reliant on BMI as a measure of adiposity will overestimate the number of individuals in the overweight (and slightly obese) categories. This tendency to misclassify individuals may be more pronounced in athletic populations or groups in which the proportion of more active individuals is higher. This differential is most pronounced in sports where it is advantageous to have a high BMI (but not necessarily high fatness). To illustrate this point we calculated the BMIs of international professional rugby players from the four teams involved in the semi-finals of the 2003 Rugby Union World Cup. According to the World Health Organisation (WHO) cut-offs for BMI, approximately 65% of the players were classified as overweight and approximately 25% as obese.

These findings demonstrate that a high BMI is commonplace (and a potentially desirable attribute for sport performance) in professional rugby players. An unanswered question is what proportion of the wider population, classified as overweight (or obese) according to the BMI, is misclassified according to both fatness and health risk? It is evident that being overweight should not be an obstacle to a physically active lifestyle. Similarly, a reliance on BMI alone may misclassify a number of individuals who might otherwise have been automatically considered fat and/or unfit.     

Exercise and bone

Abstract

The aim of this study was to examine the interrelationship between aerobic fitness, body composition, and physical activity in 9- and 15-year-olds. The 270 participants were randomly selected from 18 primary and secondary schools in Iceland. Aerobic fitness was assessed by a graded exercise test on a bicycle ergometer. Body composition was estimated via: logarithm of sum of four skinfolds (log_e skinfolds), waist adjusted for height, and body mass index (BMI). Physical activity was measured with Actigraph activity monitors using total activity each day as the physical activity variable. Aerobic fitness was chosen as the primary outcome variable, body composition as the secondary variable, and physical activity as the tertiary variable. All the full models explained a similar proportion of fitness variance for both age groups (45–65%). Among the 15-year-olds, log_e skinfolds explained a significantly larger proportion of the fitness variance (54%) than waist adjusted for height (29%) and BMI (15%), but all the body composition variables explained a similar proportion of the fitness variance (35–42%) among the 9-year-olds. Physical activity explained a smaller proportion (0%) of the unadjusted variance in fitness for the 9-year-olds than for the 15-year-olds (19%). This group difference became non-significant (0% vs. 4%) when adjusting for log_e skinfolds but remained significant when controlling for waist adjusted for height (0% vs. 15%) and BMI (0% vs. 18%). Gender differences in aerobic fitness after puberty can largely be explained by gender differences in log_e skinfolds and physical activity. In conclusion, the interrelationship between fitness, body composition, physical activity, and gender is not the same among 9- and 15-year-olds.     

Characterization of aerobically fit individuals with cardiovascular disease

Abstract

With an ageing population there is an increased prevalence of individuals living with cardiovascular disease (CVD). Characteristics of older aerobically fit individuals with previously diagnosed CVD have not been studied. Therefore, our knowledge is limited as to how, or if, aerobically fit individuals with CVD attempt to adapt their physical activity and the intensity of their training programmes. The objective of this paper is to characterise the physical activity habits and behaviours of older aerobically fit individuals with CVD. We identified 28 aerobically fit patients with CVD from those who completed a minimum of 15 and 12 min of the Bruce treadmill protocol for men and women, respectively. Consenting participants responded to questionnaires regarding physical activity levels, competitive event participation and self-monitoring since diagnosis of heart disease. Average age and treadmill time of participants were 56 and 49 years and 15.6 and 13.0 min for males and females, respectively. Data were obtained regarding recent medical history (medical diagnoses, surgeries/procedures). Despite the majority of individuals participating in the same or more activity since their diagnosis, 25% indicated that their condition limited their activity and 39% reported having symptoms during activity. Nearly all participants (93%) indicated that they monitored their heart rate during exercise. However, only 14% of participants stated that their physician advised them on how to exercise safely. It is necessary for physicians and cardiac rehabilitation programmes to be involved in safe and effective exercise programming to allow individuals to return to sport after CVD.     

A cross-cultural study of adolescents' physical activity levels in France and Spain

Abstract

The goals of this study were (1) to describe and compare levels of physical activity (PA), assessed by accelerometry, of adolescents in two close Spanish and French cities according to gender and period of the week and (2) to assess, with reference to country and gender, the extent to which international PA guidelines were fulfilled. The PA of 401 adolescents (53.37% females) from France and Spain (55.72% French) aged 14.45±0.67 years was assessed with GT3X accelerometers for seven consecutive days to evaluate their habitual levels of moderate to vigorous physical activity (MVPA). Data collection took place from September to December 2010 in six public and state schools in France and Spain. There were significant differences in MVPA in terms of country, gender and period of the week. Spanish adolescents were more active than French adolescents, boys were more active than girls and MVPA was higher on weekdays than at weekends. French girls showed the lowest level of PA. Only 35.9% of the whole sample met the guidelines for PA in both countries. Governments of relevant countries, especially France, should adopt PA promotion policies targeted at adolescents in order to enhance their compliance with PA guidelines.     

Correlates of physical activity in youth: a review of quantitative systematic reviews

To increase young people's physical activity (PA) levels it is important to understand the correlates of PA in children and adolescents. We sought to identify factors associated with children's and adolescents’ PA by reviewing systematic quantitative reviews of non-intervention research. Systematic reviews examining associations between quantitatively measured variables and PA in young people (< 19 years) from 2000–2010 were identified using electronic and manual searches. Nine systematic reviews were identified. Demographic/biological correlates of PA were age and gender. Psychological correlates of PA were positive motivation, positive body image and the existence of barriers to PA. Behavioural correlates of PA were previous PA, sport participation, smoking, and sedentary behaviour. Social/cultural correlates of PA were parental influence and social support, and environmental correlates of PA were access to facilities, distance from home to school, time spent outside, and local crime. The evidence is suggestive of a number of different types of correlates of PA for children and adolescents. Beyond age and gender, though, most are likely to have only small or small-to-moderate effects in isolation and may work best in interaction with other influences. Psychologists must look to social, organisational and community-level correlates in addition to individual correlates.     

Does current behaviour predict the course of children's physical fitness?

Abstract

The secular trend of reduced physical fitness (PF) leads to increased health risks. The aim of the present paper is to analyse various current factors that affect health behaviour with respect to the course of PF over 2 years. A path analysis combined with a latent growth curve analysis was based on a study that was conducted between June 2008 and June 2010 with 145 primary German school children (52.1% male, average age at baseline 7.95 years ± 0.95). PF was tested with the German Motor Test 6–18. For the mean PF and the course of PF, direct and indirect influences were shown over three levels, including migration background on the first level and physical activity (PA) on the second level. Body mass index (BMI) impacted the mean PF but not the course of PF. The influence of sedentary behaviour on the mean PF was diminished (compared to bivariate analysis) due to its common variance mainly with BMI. PA affected not only current PF in children but also the course of PF (a_intercept = .28, P = .001; a_slope = .27, P = .21). Consequently, preventive measures should focus on early adoption and maintenance of PA.