Prior studies noted that social participation matters, especially in an aging population with improved global healthy life expectancy [17–19]. However, few studies have focused on exploring the association between social participation and physical disability among the elderly. It is a universal question whether the observed association represents a causal effect from social participation on physical disability or just reflects a selection effect caused by unobserved (time-invariant) heterogeneity. Therefore, there were two objectives in this study. The first was to investigate the causal relationship between social participation and physical disability, and the second was to analyze methodological issues to improve empirical analysis on this topic. First of all, the F test, LM test, and Hausman test were undertaken to verify whether the fixed-effects model was more appropriate than the other models. Then, we analyzed the association between the intensity and diversity of social participation and physical disability and stratified results by gender and educational attainment. As expected, the results suggested that social participation could prevent the onset of physical disability, and there were different associations between various types of social participation and different subgroups, reflecting that it is essential to consider individual heterogeneity when viewing social participation as a public health strategy.
Health status declines as the population ages, with a substantial fall in the most elderly group . In accordance, our findings provided pertinent evidence about the apparent trend of increasing physical disability with age, and it was apparent in the elderly ≥ 85. Among the elderly, low muscle mass and physical frailty are associated with physical disabilities, and social participation might positively affect the prevention of physical disability .
Overall, this analysis showed that the elderly reporting social participation had a strong negative association with physical disabilities, which was generally consistent with Gao et al. . The possible reason might be that the elderly’s participation in social activities is a significant priority for preventing physical disability. A high participation intensity could prevent the onset of physical disability to a certain extent by being physiologically and psychologically rewarding. The former indicates that a high level of social participation might maintain physical performance and reduce the functional limitations of the elderly . The latter indicates that a high level of social participation might provide perfect opportunities for the elderly to experience positive social interactions, receive social support, and achieve happiness .
Concerning the type of social participation, household participation was associated with low risks of physical disabilities, suggesting that the elderly could develop proactive abilities from activities like cooking and taking care of children. This finding might be explained by the fact that household participation might help the elderly stay physically active, exerting direct health benefits and contributing to better functionality . Moreover, considering the Chinese cultural contexts, caring for grandchildren as a significant aspect of household participation is one opportunity for intergenerational support . This seems beneficial for mobility improvements due to increased physical activity from interacting with grandchildren .
At the same time, we should not ignore that this study did not show any significant association between leisure and sociable participation and physical disabilities. That null effect might be caused because some confounding factors and effects of mediators have not been accounted for, which could have influenced the relationship between leisure and sociable participation and physical disabilities. For instance, Aida et al.  found that the elderly living in communities with higher mistrust tended to have a higher risk for the onset of physical disability, and Garoon et al.  concluded from a qualitative study that neighborhood mistrust might lead to decreased social engagement in once-meaningful social interactions (with institutions or people) in some instances. Such an intermediate variable might lead to underestimating the association between leisure and sociable participation and physical disabilities.
Nevertheless, among the results stratified by gender and educational attainment, we further focused on the different associations between specific dimensions of social participation and physical disability. The results showed that a high participation intensity was only associated with physical disability among the female and illiterate elderly. The difference in educational attainment might also be explained from the perspective of gender difference. In China, females typically have lower educational attainment than males. The female elderly might become socially isolated more easily because of household and family responsibilities to report lower functional status levels . Therefore, the participation intensity might have a larger beneficial role among the female elderly than males.
Engaging in outdoor activities that accounts for a large proportion of the leisure participation was associated with better physical function, independently of whether the elderly was male or female, illiterate, or with primary school education. This finding coincides with past research, which suggested that physical activities like aerobic and strengthening exercises were efficient ways to improve individuals’ health status . Also, as indicated by Everard et al. , maintaining high-demand leisure activities was associated with greater physical health. Particularly, raising domestic animals in household participation might increase the risk of physical disabilities among the female and illiterate elderly. As stated above, the female and illiterate elderly are relatively disadvantaged. Considering the gender division of household labor, the female elderly may be more likely than males to be involved in a higher share of domestic chores (such as cooking, cleaning, and child care) . Raising domestic animals might cause them to be overworked and more vulnerable to physical disabilities.
Moreover, playing cards and/or mahjong, i.e., sociable participation, could decrease the risk of physical disability among the male elderly and the elderly with primary school education. Compared to the female and illiterate elderly, these groups might have more channels to connect with their society and are thus more likely to be protected against social isolation. Moreover, playing cards and/or mahjong, which is one of the most popular social activities that the Chinese elderly engage in, might improve reaction ability and memory to stimulate brain function and emotional health , leading to good physical health.
The present study had certain limitations. First, we did not control all the possible time-dependent confounders because of data limitations. Second, social participation and physical disability were based on responses to a self-report questionnaire, which might have resulted in the observed association between social participation and physical disability, overestimating or underestimating it. Third, the attrition bias of the panel data might exist. It seems that the participants with better ADLs tend to stay in the panel, and they are more likely to participate in social activities. Moreover, the results cannot be generalized to non-participants with low physical ability. Further progress will require attention to identifying the underlying mechanisms between social participation and physical disability. It is important to measure social participation and its possible mediatory effect on physical disability as various factors can affect the functional status of the elderly. In addition, we could further estimate the effects of time-invariant factors and explore inter-individual and intra-individual variations by a multilevel model.
Despite these limitations, our findings suggest that social participation has important implications for public health and social policy in an aging society. Public health interventions and initiatives might be able to prevent physical disabilities by developing social participation programs. Early detection and interventions to improve health for most elderly individuals with physical disabilities are likely to pay dividends . At the same time, more detailed and differentiated intervention strategies should be formulated, and it should be determined what kinds of social activities are necessary for the elderly, especially for the female and illiterate.