The purpose of this research was to examine the associations between MSE and depression among Chinese young adults while accounting for important third variables such as sleep and sedentary behavior. We found that about a quarter (24.87%) of Chinese young adults (university students) engaged in at least 2 days of MSE per week. Importantly, more days spent engaging in in MSE or meeting the MSE guidelines were significantly negatively related to depression severity (assessed by PHQ-9). To our knowledge, this is the first study to investigate the prevalence of MSE and its potentially protective role in preventing depression among Chinese young adults, which can advance understandings of mental well-being promotion.
Although MSE has been an imperative component of the well-recognized PA guidelines by the World Health Organization and other national public health sectors (e.g., America and Canada), research focusing on MSE and mental health benefits in various populations remains scarce . This deficiency is a barrier to better understanding physical activity in a way that is comprehensive and inclusive of various populations. The prevalence of meeting the MSE guidelines in our sample is lower (24.87% vs 28.50%) compared with one previously published study consisting of adults (from Hubei, China) over 30 years of age . This small discrepancy may be owing to different sample characteristics, such as age, and survey time (e.g., spring, summer). When evaluating the level of MSE in Chinese young adults compared with results based on Western (e.g., America, Australia) study samples, the prevalence of meeting MSE guidelines is generally lower for Chinese samples. For example, Bennie et al.  found that 29.2% of Australian adults aged 18–24 years complied with the MSE guidelines. In the US, a trend analysis on data from 2011 to 2017 indicated that over 40% of adults of 18–24 years met the MSE guidelines regardless of survey year . Taken together, the prevalence of meeting the MSE guidelines among Chinese young adults is lower compared to Western samples, pointing to the importance of intervention in young adults in order to encourage the development of lifelong healthy behaviors in this population [40–45].
Regardless of how we measured MSE in our study (e.g., days or meeting the guidelines), more days of participations in MSE or meeting the guidelines were independently related to lower risks for depression in Chinese young adults. In other words, participations in MSE could be a protective factor against depression. This research finding is consistent with prior research by Jason et al. [22, 23]. Specifically, one study based on German adults aged over 18 years (N = 23, 635) indicated that increases in MSE would be a beneficially preventive approach to treating depression. Researchers have offered some explanations as to the mechanisms that may help explain MSE’s role in decreasing depression severity or symptoms. First, more engagements in MSE can increase muscle strength that has been viewed as a health indicator and component of fitness, which improves individuals’ physical function and quality of life [46–48] resulting in decreased depression. Another mechanism examined are myokines produced by MSE that may act as a biological inhibitor against depression . In addition to these more biological mechanisms, as a form of PA, MSE could change individual psychosocial (e.g., self-esteem) and neurobiological (e.g., cerebral blood flow) factors that may both lower depression in adults . However, the mechanism associating MSE and depression should be further clarified in future research. Importantly, because our study adopted a cross sectional design, it is unreasonable to draw conclusions related to causality. Longitudinal or experimental trials to confirm the association between MSE and depression among young adults should be conducted. Altogether, this study suggests that MSE is likely a beneficial factor against depression among Chinese young adults.
Our research findings foster some important practical implications and future research recommendations to inform depression prevention. MSE is a feasible and efficient approach to preventing depression in Chinese young adults. MSE is one form of physical activity that needs few environmental supports (e.g., equipment, playgrounds). For example, individuals can conduct MSE without any equipment or instruments or perform MSE in a small space. The restrictions put in place to prevent the spread of COVID-19 in many countries, such as closing indoor gym spaces, is a testament to the versatility of MSE which many have continued or taken up in their homes. This kind of physical activity has its own merits regarding accessibility over other forms of physical activity, like swimming (need a pool) or ball sports (need balls or mates). Importantly, little is known about correlates/determinants of MSE in Chinese young adults  which is a critical component when generating campaigns to encourage young adults to conduct MSE.. Future research should examine and identify components of effective interventions to promote MSE in this population.
A major strength of this study is that we used a large sample to augment evidence on the association between MSE and depression among Chines young adults, and contributed to the evidence base for depression prevention/treatment in Chinese young adults. Another strength is that our study controlled for more variables compared with previous studies, including family-related factors, socioeconomic parameters and behavioral variables (e.g., sedentary behavior and sleep duration). However, some inherent study limitations should be mentioned. The cross-sectional study design is one limitation, which cannot fully answer the cause-and-effect association between MSE and depression. The second limitation is the use of self-reported questionnaires, which may result in recall bias. Our study sample was mainly from southern provinces in China and the generalizability of research findings into wider regions should be approached with caution. The final limitation concerns measurement, which the questionnaire to assess PA (IPAQ) did not require study participants to distinguish moderate to vigorous physical activity and MSE. This implies that IPAQ may capture MSE to some extent. However, the correlation coefficient between moderate to vigorous physical activity and MSE was 0.28 (weak correlation), indicating they are likely not measuring the same thing. Future studies should explicitly distinguish these physical activity types.