Global Recommendations on the Health of Physical Activity by World Health Organization proposes specific recommendations for the health of children and adolescents aged 5-17 years, and also proposed that children and adolescents aged 5-17 years should take health exercises in their families, schools and communities mainly to improve the health of heart, lungs, muscles and bones and to reduce the risk of chronic diseases and non-communicable diseases. It is suggested that daily activities should be more than 60 minutes [5]. The questionnaire includes question such as "how many days a week can your intensity of physical activity be more than Moderate Intensity while your physical activity lasts more than 60 minutes?" The questionnaires explained the Moderate Intensity and Vigorous Intensity, that is, Moderate Intensity is indicated as slight sweating, rapid breathing, and rapid heart beating, achieved through walking, cycling, etc. Vigorous Intensity is indicated as massive sweating, tachycardia, achieved through basketball, running, aerobics, etc. [6]. In this study, the recommended amount of physical activity is moderate to vigorous-intensity physical activity with daily activity greater than 60 mins (MVPA), and the dependent variable equals 0 when recommended amount of physical activity fails to meets the standard, and the dependent variable equals 1, when recommended amount of physical activity meets the standard.
Wang Yuesheng [7] believes that the traditional family refers to the family type with complete family members and perfect functions, mainly including the Stem Family and the Nuclear Family. According to the commonly used method of sociological research, this study divides family types into Joint Family, Stem Family and Other families, with Other Families as the reference group. They are defined as "1 = Joint Family", "2 = Stem Family" and "3 = Other Families".
The sports environment climate under family structure needs the support of social capital and the cultivation of health behavior habits. It mainly includes six variables: family expenditure on sports, community support, family-friend interaction, sense of school belongingness, campus friendship and social trust. They are all generated by Principal Component Analysis. Family expenditure on sports is mainly the parents' expenditure on sports activities for their children. The related problems are: Is family condition supportive of your needs of various sports and fitness consumption (1=not supportive,2=not supportive,3=general,4= supportive,5=very supportive) ? Are various recreational sports activities available in your neighborhood (1=never,2=seldom,3=about once a week,4=many times a week,5=every day) ? My friends often invite me to participate in fitness activities (1=never,2=seldom,3=about once a week,4=many times a week,5=every day)? I think I belong to this school. The school seems to be my home (1=very inconsistent,2= inconsistent,3=general,4=consistent,5=very consistent), I can ask for help from my friends in the school (1=very inconsistent,2= inconsistent,3=general,4=consistent,5=very consistent) ,The teachers in my school take good care of us and give us a lot of support (1=very inconsistent,2= inconsistent,3=general,4=consistent,5=very consistent). In addition to social capital, the formation of healthy behavior habits is also crucial to the healthy development of children and adolescents' physique. In this study, dietary behavior, sleep behavior, decompression behavior and exercise behavior are selected as the main indicators of healthy behavior habits evaluation. Principal Component Factor Analysis (PCA) was used to analyze the health behavior variables. The related problems are: I have enough intake of protein, vegetables and fruits to maintain nutritional balance every day (1= very inconsistent,2= inconsistent,3=general,4=consistent,5=very consistent), I can punctually go to bed and get up every day and learn regularly (1=very inconsistent, 2=inconsistent, 3=general, 4 =consistent, 5=very consistent), I can respond positively to difficulties (1=very inconsistent, 2=inconsistent, 3 = general, 4 = consistent, 5 = very consistent), number of weekly fitness activities (1 = never participated, 2 = 1 - 2 times a week, 3 = 3-4 times a week, 4 = 5 times a week, 5 = once a day).
Based on the assignment of dependent and independent variables, the hypotheses of this study are put forward: (1) the family structure differences of physical activity among children and adolescents have shown a diversified development trend, (2) the more stable the family structure is, the better the family sports atmosphere will be, (3) the hierarchy of family structure has a positive effect on shaping children's adolescent health behavior, (4) the better the social capital is, the better the community sports atmosphere will be, and the higher the possibility of children and adolescents completing the recommended amount of physical activity will be.
In this study, the author conducted survey in 13 provinces and cities in China in 2018, such as Heilongjiang, Beijing, Liaoning, Shandong, Zhejiang, Henan, Hubei, Guangdong, Sichuan, Gansu, Yunnan, Guizhou, and Chongqing. The survey targets children and adolescents aged 7-18. With National Student Physical Fitness and Health Survey Implementation Plan in 2014 as the data information collection benchmark [8], a three-stage sampling survey was conducted in 13 provinces and cities using the PPS sampling method. 1180 counties (districts and municipalities) of 13 provinces (cities) were used as primary sampling units, and cluster sampling was carried out according to the order of Tabulation on the 2010 Population Census of the People's Republic of China by County. In the first stage, 15 counties (autonomous regions and municipalities) in each county (city) were selected as samples for random sampling, and a total of 195 survey counties (districts and municipalities) were selected. In the second stage, the sample counties were screened in a small scale, and 4680 administrative classes were randomly selected from the first grade of primary school to the third grade of senior high school. In the third stage, a second random sampling was conducted in the selected classes. 20 samples were selected in each administrative class, and the final sample of 93600 students was obtained.
Before the investigation, every researcher has been trained in strict data input requirements, so that they can understand the source and use of data in the process of investigation. In the process of data input, the working procedure of two-person input and verification is adopted to ensure the accuracy and rigor of data input, eliminate the data deviation caused by personal factors, and strictly conduct rigorous checks on the logicality and rigor of data. The control variables mainly include: gender (1 = male, 2 = female), family type is divided into ("1 = Joint family", "2 = Stem family", "3 = other families). Social capital and health behavior include six variables: family expenditure on sports, community support, family-friend interaction, sense of school belongingness, campus friendship and social trust, which are generated by principal component analysis.
Based on the basic characteristics of physical activity of children and adolescents, this paper used multi-level logistic regression model to verify the research hypothesis. To differentiate the intra-group and inter-group variations of the model, a zero-model is established to analyze the significance of the difference of social capital to dependent variables, to judge whether the multi-level model is valid, and to analyze the influence of the change of social capital on dependent variables. Regression equation significance test was used to test the fitting degree of the model. The significance level was below 0.05. Pearson significance P value was observed.