Since the reform and opening up in 1979, the social status stratification in China has declined, the socioeconomic stratification has risen, and the social structure has also undergone significant changes. The following research assesses the changes in people and groups, and it is these changes that promote the continuous progress of reform. The purpose of the reform is to promote social progress and realize social equity. The issue of social equity and the understanding of people's structural status in society is an eternal academic topic, and the sports field is no exception. In past research, we were constantly trying to find the motivation, conditions and purpose of group education and exercise of a group of people. It is undeniable that the research results of individual or labeled people's physical exercise have deepened our understanding of sports. However, it is precisely because of this kind of research thinking that the research lacks analysis of the influencing mechanism of stratification factors on physical exercise. Specifically, there are two kinds of deviations: one is to blur the concept of socioeconomic status, and the other is the lack of analysis on the impacts of subjective class identification and socioeconomic status on physical exercise. These two kinds of deviations also indicate the complexity of the influences of subjective class identification and socioeconomic status on physical exercise because the social objective fact of physical exercise behavior is intertwined with people's subjective psychology and economic status, and they influence each other. From the perspective of the explanation of the effects of subjective class identification and socioeconomic status on physical exercise, subjective class identification is mainly based on the chosen relationship of individual consciousness, perception and action. Furthermore, it advocates following the interpretation logic of "from consciousness to action" to realize the position of an individual stratum to choose whether to participate in physical exercise, and socioeconomic status is affected by a variety of social variables. This is similar to Hu Rong's (2014) (Rong, 2014)research on the perception of the social position of Chinese residents. In addition to income, occupation, education and other factors, socioeconomic status is also affected by a person’s perception of their own position, which leads to inconsistency between the subjective class identity and socioeconomic status(Rong, 2014).
In this sense, examining the issue of physical exercise from the perspective of subjective class identification and socioeconomic status provides us with another perspective to examine the issue of sports equity and increase the amount of physical exercise of the population. Therefore, based on the redefinition of the impact of subjective class identification and socioeconomic structure on physical exercise, this paper aims to explore the influence mechanism of the social stratification structure and physical exercise behavior from the perspective of social stratification and conduct an empirical estimation using the 2015 China social survey data (CGSS).
Theoretical analysis and research hypotheses
In the traditional and modern sociological analysis and research, subjective class identification and socioeconomic status have always been the basic propositions studied by sociology. Marxist sociological theory holds that class status determines class identity. Weber thinks that multiple social stratification standards reveal the multidimensional nature of objective social stratification. Jackman and his wife believe that class identity is people's self-perception of their social class position(MR，JachmanR., 1973).Structural functionalism holds that the stratification in industrial society is in line with the actual needs of the overall social function and is conducive to the smooth operation of society. The high and low differences within the society are just the differences in quantity, and the "crystallization" and "convergence" of various factors affect this stratification difference (B.Grusky, 2005). What can be determined is that social stratification is an objective existence. As long as we are in society, it will be linked with social stratification. People usually use the concept of socioeconomic status when determining and comparing the differences between people's social strata. Socioeconomic status is based on the comprehensive score calculated based on an individual’s education level, income level and professional reputation. In general, a person's socioeconomic status and access to social resources are roughly the same(Hangsheng, 2014) .
All kinds of problems of the social stratum will also appear in participation in physical exercise through various forms of expression, or the social equity problems caused by social strata will also be reflected in the objective facts related to physical exercise. Due to the social class gap, the lack of some rights of citizens and so on, no one in society can mention it, which may be the main reason for the lack of equity in sports participation opportunities(Jingguo, 2010). Therefore, this paper attempts to examine the influence mechanism of social stratification structure and physical exercise behavior from the perspective of three hypotheses of subjective class identification and objective socioeconomic status on physical exercise, namely, "dynamic theory", "structural theory" and "subjective and objective theory".
Subjective class identification and socioeconomic status in the "power theory" of physical exercise
From the perspective of the social structure, subjective class identity and socioeconomic status reflect certain social class group characteristics. Previous research results show that subjective class identity and socioeconomic status and the possibility of physical exercise are positively correlated. Among them, the research of Man (Jianghong, 2016)and Li(Haijie, 2017)shows that the higher the subjective class identity of urban residents is, the higher the degree of sports participation, which is mainly due to the higher social class's higher share of cultural capital(Ma Jiangtao, 2014) . Tian studied the relationship between social class status and sports participation and found that the higher the social class status, the higher is the proportion of sports participation(Tian Xueli, 2014). It can be seen that, both subjectively and objectively, physical exercise can become a cultural distinction to judge a person's tastes and style. The reason is nothing more than the different understandings and needs of different classes of groups for sports under the intervention of their "field" and "habits"(Xu Feng, 2012). This also shows that the behavior of sports participation can not only shape people, but it can also be recognized and dominated by individuals(Liu W, 2011). In terms of the dynamic effect of subjective class identification and socioeconomic status on physical exercise, Li Xiaotian thought that the physical exercise of urban residents was affected by both individual and high-level independent variables(Li Xiaotian, 2019). Aron used the method of multiple correspondences and found that the social economy and culture play mediating roles in sports participation preferences (R, 2012). To sum up, the level of the subjective class and socioeconomic status promote the frequency of physical exercise. Therefore, this paper puts forward the hypothesis of "dynamic theory".
Hypothesis 1: In physical exercise participation, the objective socioeconomic status and subjective class identity have significant influences.
The "structural theory" of the effects of subjective class identification and socioeconomic status on physical exercise
The gap between the rich and the poor will be reflected in their physical exercise. LV Shuting (2006) once found that in Guangzhou, the highest proportion of the population participating in sports is the upper class of society, and the lowest proportion of the population participating in sports is in the middle and lower strata of society (Shuting, 2006). Support shows that social class differences affect people's physical exercise. In addition, subjective stratum identification may have strong explanatory power in terms of social attitudes, political preferences and collective action, which can provide supplementary and confirmatory information for socioeconomic status (LIlulu, 2018). From the perspective of internal social aspects, the structure of subjective class identity and socioeconomic status will inevitably lead to structural differentiation. The most important thing for an individual's subjective class is the group structure and "reference group" in which people form their own class identity and behavioral choices (Merton, 2006). Some studies have shown that the socioeconomic status and subjective class identity of residents tend to generally trend downward (Chune, 2008), which may be closely related to the excessive pressure of residents' economic life and the weak sense of gain. In the empirical research on physical exercise and stratification, Wu explained this difference from the perspective of the functions of sports, that is, the middle and upper groups are better at exploring the multiple functions of sports, such as fitness and social interaction, while the middle and lower groups still view sports as a single traditional function(Wu Zhenhua, 2008). Chen through the investigation and research of Hangzhou, Ningbo and Wenzhou, found that there is a certain proportional structure for all social strata to participate in physical exercise, but the participation will increase as the social stratum improves (Chen JIhang, 2009). Li believes that the possibility of high class physical exercise is also high, mainly due to personal income, education and leisure time (Li Xiaotian, 2019). Han Qiuhong (2015) compared the influence of the internal structure on the differences in physical exercise. Han thought that the urban residents in the middle and upper social classes were more active in physical exercise than those in the upper and middle lower classes (Qiuhong, 2015). The reason for this internal structural difference is that the cultural capital of the middle and upper classes of society is higher, and the awareness of sports and cognitive levels are also higher for those classes than for other classes (Yifeng, 2015); however, there are also some scholars that believe that the influencing factors of social structural differences in physical exercise tend to be more diverse as the social stratum rises (Tang Guojie, 2009). In view of this, this paper puts forward the "structure theory" competition hypotheses:
Hypothesis 2A: In physical exercise participation, there is a big gap in the internal structure of subjective class identity.
Hypothesis 2B: In the physical exercise participation, there is a big gap in the internal structure of socioeconomic status.
Subjective class identity and socioeconomic status
Whether the subjective class identity and socioeconomic status play independent roles when influencing physical exercise or whether they have a kind of dependency relationship will be the research focus of this paper. In fact, socioeconomic status and subjective class identity are self-adjusted by other social variables. Feng Shizheng (2011) believes that the "middle class identity" of Chinese residents is decreasing while the "low-level class identity" is expanding. The reason is that social capital affects people's socioeconomic status and it affects people's subjective class identity. This study shows that socioeconomic status affects the formation of subjective class identity(Zhang Shun, 2012) . Liu believes that in terms of the economic conditions that restrict people's participation in sports, the economic conditions from the upper middle class to the middle level and then to the middle and lower levels gradually decrease(Liu Wei, 2011). In terms of the subjective and objective theory of social class identity, Chase thinks that socioeconomic status has a significant impact on an individual's class identification, and an individual's political status, educational capital, social capital and economic capital have positive effects on subjective class identification. In addition, a personal sense of gain will also enhance personal class identity, that is, satisfaction with life improvements and a sense of gaining success (Sisi, 2018). It can be seen that subjective class identity will have an upward or downward cognitive bias as the variables included in socioeconomic status change. Some people also believe that in physical exercise behavior, subjective class identification only plays a mediating role. Li thought that human behavior and its practice is affected by individual subjective consciousness, concepts and self-cognition, among which subjective identity is an important intermediary variable; and the result of human behavior and its practice is the result of the joint action of objective structure and subjective perception (lulu, 2018). To investigate the results of physical exercise behavior, we should not only investigate the objective structure, but we should also investigate the subjective understanding. Man used structural equation modeling analysis to find that urban sports residents' class identity plays a partial intermediary role in the path from income to sports participation (Jianghong, 2016), which shows that class identity plays a role through individual income; in other words, individual economic income level affects individual class identity. To sum up, the subjective class identity and the objective economic status do not play independent roles, but there are subjects and objects in the influence mechanism.
In view of this, this paper puts forward the "subjective and objective" competition hypotheses.
Hypothesis 3A: In physical exercise participation, subjective class identity is the main variable.
Hypothesis 3B: In physical exercise participation, socioeconomic status is the main variable.