Millions of people across the world struggle to control the risk factors that lead to CVD, many others remain unaware that they are at high risk, a large number of heart attacks and strokes can be prevented by controlling major risk factors through lifestyle interventions and drug treatment where necessary . The risk factors for CVD include behavioral factors, such as tobacco use, unhealthy diet and inadequate physical activity , which could be used to assess the risk of CVD and identify major behavior patterns associated with CVD.
The China Kadoorie Biobank (CKB) study  reported that total physical activity  was strongly and inversely associated with CVD mortality. People have gradually changed from a labor-intensive lifestyle to a sedentary lifestyle, with both occupational and leisure physical activities decreased in recent decades among Chinese people . A prospective cohort study of 487,334 subjects conducted by Bennett et al  in 10 regions of China showed that higher occupational or nonoccupational PA was significantly associated with lower risk of major CVD among Chinese adults.
Through the PCA of participants’ PA, this study found that it could be summarized as three groups of different PA types (Latent Classes): CLASS1 (high occupational and low sedentary PA), CLASS2 (low occupational and high leisure-time PA) and CLASS3 (low leisure-time and high sedentary PA). Several previous LCA studies provided limited and varied findings in different fields, such as sociology, biology, medicine and psychology. To our knowledge, our study is one of the first studies to identify associations between CVD and PA among Chinese adults using LCA with representative data.
This study showed that CLASS3, i.e. people with low levels of PA, accounted for a big proportion in the three categories (40.9% for males and 59.3% for females). As can be seen, the main PA behavior of CLASS3 is manifested as high sedentary and low leisure-time activity behavior generally. A survey of nine provinces in China from 1991 to 2011 found that for both adult men and women in China, occupational and domestic PA were by far the largest contributors to PA, the residents' overall PA was significantly decline and active leisure and travel PA were both low. Quite a few studies in China such as have also shown that the occupational PA was the most widespread PA in Chinese residents currently, while the leisure PA was reversely low [35, 36]. Inadequate physical inactivity has become one of the major risk factors for CVD death and disease burden in China .
This study explored the differences in the 10-year risk of CVD among the three types of PA predicted by the Framingham risk scoring system. The results showed that the 10-year risk of CVD in male was 2 to 3 times higher than that in female in all three categories. Previous studies [38, 39] indicated that male generally had a higher risk to develop CVD events, which may be related to differences in exposure levels and sensitivities of risk factors for CVD between genders, in addition to sex hormone differences. Both gender showed CLASS3 CVD risk higher than that of both CLASS1 and CLASS2, after the adjustment of confounding factors, found that the risk of CVD in CLASS3 in males was 1.44, 1.34 times compared to CLASS1 and CLASS2.This result is consistent with Petagna’s  adult health longitudinal study and Li’s  Meta-analysis consisting of 21 prospective studies involving 20000 patients with CVD definitely. As a result, the 2018 PA guidelines for Americans  emphasize that increasing PA and reducing sedentary time are appropriate for all populations, and that even a little increase in PA can bring health benefits. According to the American college of sports medicine (ACSM) , regular PA (such as exercise, cycling, etc.), may reduce insulin levels and renal sympathetic nerve tension by sodium retention and foundation, vasodilator substances by skeletal muscle release cycle, and can improve blood pressure, blood lipid and blood glucose and other risk factors .
The method of the LCA takes account the comprehensive effect of multiple factors, can reveal the characteristics of various groups of people and provide scientific basis for the designation of targeted intervention and prevention measures. However, several limitations of the study should be considered. First of all, the LCA takes the qualitative data into consideration, instead of the comprehensive analysis of its frequency and duration. Secondly, using the method of questionnaire survey to collect physical activity information, rather than using objective measurements (e.g. using pedometers to calculate the exact daily steps), may lead to recall bias. Nevertheless, the use of a tool with proven validity and reliability, i.e. the GPAQ, together with adequate staff training, can minimise such bias. Limited by a cross-sectional design of the study, it is hardly to explain the causal relationship of PA and the risk of CVD and further robustly designed longitudinal research are warranted to test this relationship.
To summarize, the study reveals potential associations between CVD and PA patterns among Chinese adults, with the lower occupational and leisure-time PA and higher sedentary PA related to increased risk of CVD. Accordingly, we suggest relevant sectors in China strengthening evidence-based interventions in order to increase PA and reduce the time of sedentary behaviors. Findings from this study can bring contributions to public health, particularly in the management of public policies that promote PA and bring more health benefits.