Introduction

Depression is a common psychological disorder that manifests as depressed mood, slow thinking, pessimism, lack of initiative, and even the tendency or behavior of self-injury, suicide, or homicide in severe cases. In recent years, the number of Chinese college students suffering from depression has been high due to the increased pressure on study, life, and employment. The survey data of the 2022 National Depression Blue Book shows that the number of depression patients in China has reached 95 million, of which 50% are school students, and 41% have been suspended from school due to depression (Huang, 2022). Depression has become the primary disease in the mental health of college students, which seriously affects the development of sound personality of college students (Wang, 2014). Physical exercise can not only improve health and improve the ability of human body to resist disease, but also regulate and promote the development of human psychological activities in a healthy direction (Fu, 2006), effectively reduce the degree of depression and relieve anxiety symptoms of patients (Strohle, 2009). In the field of sports psychology, many scholars have explored the positive role of physical exercise in reducing depression and promoting mental health. Among them, Xu (2021) found that physical exercise can effectively enhance the level of mindfulness of college students, and through mindfulness, physical exercise can effectively regulate and improve the psychological state of exercisers and reduce the level of depression; Xia et al. (2023) concluded that physical exercise can improve college students’ sense of the meaning in life, and that the sense of the meaning in life has a positive effect on overcoming the adverse symptoms of individual anxiety and depression (Gu, 2007). As a result, domestic research shows that physical exercise can not only improve the psychological state of individuals through mindfulness but may also reduce the depression level of individuals through the meaning in life. Compared with domestic studies, Western scholars rarely discuss the relationship between these variables, but the research results on the role of physical exercise in promoting mental health, such as physical exercise can improve mood (Fossati et al. 2022), reduce depression (Devi & Rani, 2013), improving the quality of life (Moreno-Murcia, 2017), etc., can still provide important theoretical basis for this study. On this basis, this study intends to build a mechanism model of physical exercise on depression in Chinese college students, and then examine how physical exercise affects Chinese college students’ depression through mindfulness and meaning in life, so as to broaden the breadth of the research on the psychological effects of physical exercise, and at the same time, it provides guidance for strengthening the intervention effect of physical exercise in concrete practice and reducing the depression level of college students.

Theoretical basis and hypothesis

The relationship between physical exercise and college students’ depression

With the increase of research in the field of sports psychology, people began to recognize the psychological benefits of exercise, such as exercise can reduce individual anxiety and depression by regulating dopamine, endorphin and other neurotransmitters. At the same time, people have also been a lot of research on the brain mechanism of exercise to reduce depression and other negative emotions. The cross-sectional studies show that physical exercise has a significant negative effect on college students’ depression (Olmedilla, 2010; Zhang, 2022), the results of longitudinal studies also confirm that physical exercise interventions have a negative effect on college students’ depression levels (Yang, 2021), and appropriately increasing physical exercise can effectively improve the depressive state of college students and is beneficial to the development of psychological health (Song et al., 2017). One acute exercise and aerobic exercise lasting four weeks or longer significantly reduced the depression level of female college students (Wang, 2014). Confrontational and non-confrontational physical exercise can significantly reduce depression among college students (Tang et al., 2009). Compared with individual sports programs, group sports programs are more effective in reducing depression among college students (Wang et al., 2008). Exercise time, exercise frequency, and exercise intensity all affect the relationship between physical exercise and college students’ depression (Xiao et al., 2022).

Because of this, this study proposes hypothesis 1: Physical exercise negatively predicts depression levels in college students.

The mediating role of mindfulness

Existing exercise psychology shows that physical exercise has many psychological effects. As an important psychological resource for maintaining and promoting mental health, mindfulness can improve the function of brain areas related to excitement and pressure, and reduce anxiety by adjusting emotions. Mindfulness is the ability of an individual to remain aware and attentive to the experience of the present moment in a non-responsive, non-judgmental, and broad-minded manner (Brown et al., 2009). Although it is a trait that individuals are born with, acquired factors such as appropriate education and intervention have a greater impact on mindfulness (Duan, 2014). The attitude of physical exercise is inclusive and receptive, and has a high similarity to the “attitude without evaluation” of mindfulness. Therefore, the psychological structure of physical exercise and the mental structure of mindfulness have a high compatibility. In addition, the study found that mindfulness is significantly and negatively correlated with many vital influences of depression, such as ruminative thinking, mental rigidity, and experiential avoidance (Xu, 2018). Through mindfulness practice can effectively treat anxiety, depression and other psychological disorders (Hilton et al., 2017; Lee et al., 2015). Because of this, this study proposes hypothesis 2: Physical exercise positively predicts the level of mindfulness.

The mediating role of the meaning in life

Meaning in life refers to how individuals understand and identify with their life goals, personal missions, and values (Steger et al., 2006). Existential psychology points out that the pursuit of the meaning of life is one of the distinctive characteristics of human beings. Frankl believed that people’s exploration of the meaning of life was the driving force of their lives, and the meaninglessness of life would lead to boredom, anxiety and depression, and they would experience the vacuum of existence. Such existential emptiness might lead individuals to psychic neuroses (including depression and addiction) (Zhao, 2013). The core idea of existentialist psychology is to pay attention to “human existence”, and people experience the meaning of life through self-realization, which is very consistent with the traditional social value of the East, which attaches importance to “humanities” and ignores empirical science, such as “ethics” which attaches importance to people’s “own existence”, “I think about my body three times a day” in the Analects of Confucius. In fact, it means that people should always pay attention to reflect on their own “existence” every day. As a positive psychological resource, meaning in life has a positive predictive effect on individuals’ physical and mental health (Xia et al., 2023). People with a lack of meaning in life can cause individuals to develop negative emotions such as anxiety, depression, and even suicidal tendencies (Zhang, 2020). Studies have shown that physical exercise can improve college students’ meaning in life (Xia et al., 2023), positively impacts individuals’ negative emotions, such as anxiety, and has outstanding benefits in enhancing subjective well-being and releasing vitality in life (Gu, 2007). College students who regularly engage in physical exercise have higher overall levels of meaning in life (Chen et al., 2005).

In light of this, this study proposes hypothesis 3: physical exercise positively predicts meaning in life.

Construction of the chain mediator model

The extension-construction theory of positive emotions points out that positive emotions can expand individuals’ positive thinking and behavior paradigms, and help induce individuals to extract more meaning-related information, thus enhancing the meaning of life and increasing individual happiness (Fredrickson, 2001). A series of empirical studies have found that positive emotion is an effective predictor of individual life meaning (Liu et al., 2020), and mindfulness is an important means to stimulate individual positive emotion (Allan et al., 2015). The higher the individual’s level of mindfulness, the higher the meaning of life; Conversely, when an individual’s level of mindfulness is low, its significance is also low (Boehm, 2017). Hsieh (2021) examines the relationship between marginalization, mindfulness, and meaning in life. The results show that mindfulness is positively correlated with the meaning of life, and mindfulness can alleviate the frustration of marginalized people to a certain extent, thus enhancing the meaning of life. In addition, a study of 764 students using self-report methods found that meaning in life mediates the relationship between mindfulness and depression (Segal & Williams, 2012).

Accordingly, this study proposed hypothesis 4: mindfulness and meaning in life mediate between physical exercise and depression.

In summary, to examine the effect of physical exercise on depression in college students, this study proposes to construct a chain mediation model (as shown in Fig. 1) and will test the following aspects: (1) physical exercise significantly and negatively predicts depression; (2)mindfulness and meaning in life play a separate mediation role between physical exercise and depression; (3)mindfulness and meaning in life play a chain mediation role between physical exercise and depression in college students; (4)mindfulness and meaning in life play a mediating chain role between physical exercise and depression in college students.

Fig. 1
figure 1

Conceptual framework

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Research participants and methods

Participants and sampling

A convenience sampling method was used to investigate the mediating effect between physical exercise and depression using the Physical Exercise Rating Scale, Depression Scale, mindfulness Scale, and Meaning in Life Scale on 1021 college students from 8 Liaoning Province and Jiangsu Province universities. A total of 954 valid questionnaires were recovered, with a recovery rate of 93%, including 506 male college students (53.04%) and 448 female college students (46.96%). Among the recovered questionnaires, those with one of the following problems were regarded as invalid and deleted: (1) inconsistent responses to the reverse scoring questions; (2) too short response time; (3) There is a clear pattern of repetition in the choice of answers, such as 1, 2, 3, 1, 2, 3.

Research tools

Physical exercise rating scale

This scale was revised by Liang (1994), and it has high reliability and validity by measuring three dimensions of physical exercise intensity, duration of each exercise, and the number of exercises per week of the participants. The scale was scored on a 5-point Likert scale, with higher total scores indicating greater physical exercise. The scoring method is exercise = intensity × (time-1) × frequency, with a maximum score of 100 and a minimum score of 0. In this study, it was verified that the scale has good reliability and validity. The internal consistency reliability a coefficient was 0.879, and its internal consistency coefficient α of each dimension were 0.86, 0.84, and 0.79, respectively; χ2/df = 2.548, TLI = 0.916, IFI = 0.926, CFI = 0.928, NFI = 0.915, and RMSEA = 0.071.

Beck depression inventory

This study used the 13-item version of the Beck Depression Inventory compiled by Zhang (1998), which was developed by the American psychologist Beck AT based on the 21-item version, and the correlation coefficient between the two versions reached 0.96. The items of the scale were scored on a four-point scale from 0 to 3 (0 = no such symptoms; 1 = mild; 2 = moderate; 3 = severe), with higher total scores indicating a higher tendency to depression, where 0 to 4 is essentially no depressive symptoms, 5 to 7 is mild, 8 to 15 is moderate, and 16 or more is severe. In this study, it was verified that the scale has good reliability and validity. Its internal consistency coefficient α = 0.915; χ2/df = 2.712, TLI = 0.924, IFI = 0.918, CFI = 0.927, NFI = 0.941, and RMSEA = 0.065.

Mindful attention awareness scale

The Chinese version of the Mindful Attention Awareness Scale (MAAS) was revised by Chen (2012). The scale has 15 items and is unidimensional, and is scored on a 6-point Likert scale, ranging from “never” to “almost always,” with a score of 1–6. In this study, it was verified that the scale has good reliability and validity. Its internal consistency coefficient α = 0.922; χ2/df = 2.535, TLI = 0.931, IFI = 0.915, CFI = 0.908, NFI = 0.927, and RMSEA = 0.062.

Meaning in life questionnaire

The meaning in life questionnaire (MLQ) developed by Steger et al. (2006) and revised by Liu and Gan (2010) was used, with ten items containing two dimensions of meaning-seeking and meaningful experience of life, each with five questions. A 7-point Likert scale was used, with higher scores indicating a stronger meaning in life. In this study, it was verified that the scale has good reliability and validity. Its internal consistency coefficient α = 0.953, and the internal consistency reliability alpha coefficients of each dimension were 0.869 and 0.802, respectively; χ2/df = 2.721, TLI = 0.918, IFI = 0.925, CFI = 0.914, NFI = 0.909, and RMSEA = 0.070.

Data statistics and analysis

SPSS 26.0 with the plug-in Process was used to analyze the data, including internal consistency tests, Pearson correlation coefficient analysis, regression analysis, and Bootstrap method tests for bias correction for the physical exercise scale, the mindfulness scale, the meaning in Life scale, and the depression scale. The Bootstrap method test was conducted with a sample size of 5000 and a confidence interval of 95%, where a confidence interval without zero was considered significant and vice versa. In addition, the Power analysis software G*Power was used to calculate the sample size of the questionnaire survey. Among them, the effect size was set to 0.3, the significance to 0.05, and the statistical power to 0.8. Finally, the required sample size was calculated to be 82.

Research results

Common method bias test

In order to avoid the influence of common method bias on the study results, necessary controls were performed during the actual testing process, such as requiring the participants to answer anonymously and using reverse scoring for some entries. The Harman one-way test was also applied to test for common method bias. The results showed that there were nine factors with eigenvalues greater than one, which explained 70.10% of the variance, and the amount of variance explained by the first factor was 30.76%, which was less than the critical value of 40%, indicating that there was no serious problem of common method bias in this study.

Descriptive statistics and correlation analysis of each variable

Independent samples T-test was used to analyze the differences in physical exercise, depression, mindfulness, and meaning in life by gender, and the results showed that male college students were better than female college students in physical exercise, depression, mindfulness, and meaning in life, showing significant differences (Table  1).

Table 1 Differences in gender
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One-way ANOVA was used to compare the differences in physical exercise, depression, mindfulness, and meaning in life among different grades. The results showed that physical exercise was significantly different among college students of different grades, and overall, lower grades were better than higher grades; depression level was significantly different among college students of different grades, with juniors having the lowest depression level and seniors having the most severe depression level. There was no significant difference in the level of mindfulness and meaning in life among college students each year (Table 2).

Table 2 Differences in grades
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The Pearson correlation analysis was performed for each variable, the results are shown in Table 3. There was a significant positive correlation (p < 0.01) between physical exercise, mindfulness, and meaning in life and a significant negative correlation (p < 0.01) between physical exercise, mindfulness, meaning in life, and depression. It indicates that the higher the level of physical exercise, the stronger the mindfulness and meaning in life, and the lower the level of depression, and hypothesis 1 was verified. Because grade was significantly correlated with physical exercise and depression, and gender was significantly correlated with physical exercise, depression, mindfulness and meaning in life, both were studied as control variables in the subsequent regression analysis (Table  3).

Table 3 Descriptive statistics and correlation coefficients of each variable
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Since all variables are significantly correlated and may have the problem of multicollinearity, which causes unstable results, this study performs a covariance diagnosis. It standardizes the predictor variables in each subsequent equation (Z-score). The results showed that the VIF values (1.327–2.458) of all variance inflation factor (VIF) predictor variables were less than 5. The data has no multicollinearity problem, which meets the conditions for further testing the chain mediation effect.

Structural equation modeling analysis

In this study, the structural equation modeling test analysis was conducted using the great likelihood method to measure the degree of fit of the structural equation model to the actual data. The results show that the model fits the data well: χ2/df = 2.54, RMSEA = 0.09, NFI = 0.92, GFI = 0.93, CFI = 0.93, and all fit indices are above the standard of 0.9.

Significance test of the mediation effect

Using physical exercise as the independent variable, mindfulness and meaning in life as the mediating variables, and depression among college students as the dependent variables, the SPSS plug-in PROCESS macro program provided by Hayes (2013) was used to test for chain-mediated model effects using the Model 6 mediation model with grade and gender as control variables, where Bootstrap Samples were set to 5000 and the default 95% confidence interval, which is significant when the confidence interval does not contain 0. The results showed that physical exercise was a significant predictor of depression in college students before the mediating variable was included (β= -0.147, t = -4.384, p < 0.001). When the mediating variables were put in, the predictive effect of physical exercise on college students’ depression was not significant (β = 0.042, t = 1.096, p > 0.05). However, the predictive effects of the mediating variables were all significant, including the path coefficient (β) of physical exercise on mindfulness was 1.593, the path coefficient of mindfulness on depression was − 0.077, and the path coefficient of physical exercise on the meaning in life was 0.374. The path coefficient for meaning in life on depression was − 0.067, and the path coefficient for mindfulness on meaning in life was 0.383 (Table 4 with Fig. 2).

Table 4 Regression analysis of physical exercise, mindfulness, and meaning in life on depression
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Fig. 2
figure 2

Chain mediation model of social support influencing exercise adherence (N = 954)

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The results of the mediation effect test using the bias-corrected percentile Bootstrap are shown in Table 5. The total mediation effect value of mindfulness and meaning in life between physical exercise and depression in college students was − 0.189, and the Bootstrap 95% confidence interval did not contain 0, indicating that the total mediation effect of physical exercise and depression in college students was significant. The total mediating effect consists of three paths: Ind1: the path mediated by mindfulness, with an effective value of 0.123; Bootstrap 95% confidence interval does not contain 0, indicating a significant mediating effect, and research hypothesis 2 is verified; Ind2: the path mediated by the meaning in life, with an effective value of -0.025, Bootstrap 95% confidence interval does not contain 0, indicating a significant mediating effect, and this result verifies hypothesis 3; Ind3: path with mindfulness and meaning in life as chain mediators, with an effective value of -0.042, Bootstrap 95% confidence interval not containing 0, and a significant chain mediating effect, and this result verifies hypothesis 4.

Table 5 Bootstrap analysis of significance test of intermediary effect
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Discussion

To explore the intrinsic mechanism of physical exercise affecting college students’ depression, this study constructed a chain mediation model mediated by mindfulness and meaning in life. The results of the study reveal the intrinsic mechanism of the effect of physical exercise on college students’ depression and also provide an empirical basis for improving college students’ depression and promoting their mental health.

Relationship between physical exercise and depression

The results of this study confirmed that there is a significant negative correlation between physical exercise and depression among Chinese college students, and the greater the physical exercise amount, the lower the depression level of college students, which is consistent with previous research results (Jiang et al., 2017). At the same time, studies on other groups, such as adolescents (Boone & Brausch, 2016), adults (Kim, 2022), and the elderly (Hidalgo, 2021), have also shown a significant negative correlation between physical exercise and individual depression. Studies have shown that physical exercise can not only effectively improve people’s mental health level, but also significantly improve people’s mental health problems. Physical exercise can make people happy by regulating the level of neurotransmitters such as endorphin and dopamine in the human body, thus reducing the level of depression (White et al., 2009). The self-efficacy hypothesis holds that individuals can enhance their sense of self-efficacy through physical exercise, thereby increasing their confidence in coping with depression (White et al., 2009; Tang et al., 2022). This study also concluded that under the Chinese cultural background, male college students have more physical exercise and lower depression level than female college students, which is consistent with the results of Edman et al. (2014). This may be because male college students are more likely to exhibit strong gender characteristics and are more willing to gain more interpersonal attention through their muscular bodies (Yin, 2021), and because women are more sensitive to negative and positive emotions, female college students generally have higher levels of depression and anxiety than male college students. In addition, lower school students had higher levels of physical activity than older students, and seniors had the highest levels of depression. This may be due to the pressure of graduation and employment after entering the senior study period (Terrell et al., 2022), limited disposable time, resulting in insufficient physical exercise.

Mediating role of mindfulness and meaning in life

The present study found that mindfulness mediated the relationship between physical exercise and depression among Chinese college students, a result consistent with previously reported findings (Yang et al., 2023). Studies have shown that the psychological effects of physical activity are mainly in the modulation of positive emotions such as subjective satisfaction and subjective happiness and the suppression of negative emotions such as depression and anxiety (Xu et al., 2014). In sport psychology, the role of mindfulness in improving individual self-regulation, increasing individual life satisfaction, and reducing depression levels has received increasing attention. For example, Cheng (2015) found in his study that group positive thinking training for adolescents with depressive symptoms can improve the level of positive thinking and depressive symptoms, especially in the prevention of depression recurrence, positive thinking training has a better intervention effect (Segal, 2012). Meaning in life refers to an individual’s perception and feelings about the meaning and value of self-life. As a positive health-related variable, it is significantly negatively correlated with depression (Liu et al., 2012) and can reduce the risk of suicide due to adverse life events (Xiao et al, 2018). The findings suggest that meaning of life predicts individuals’ well-being and health, predicts individuals’ negative emotions, and plays a moderating role in stress and depression (Zhang et al., 2018). Individuals with higher meaning in life have higher life satisfaction (Liu, 2022), lack of meaning in life of individual college students is significantly and negatively correlated with individual loneliness and suicidal ideation (Castano et al., 2022), and individuals with low meaning in life show more depressive symptoms (Parra, 2020). The study of the relationship between physical activity and personal meaning in life has received the attention of many scholars. Findings suggest that there is an interaction between physical activity and personal meaning of life, and that individuals with high meaning of life also have better physical activity behaviors.

The mediating chain effect of physical exercise on depression

The present study found that mindfulness and sense of meaning in life play a chain-mediated role between physical activity and depression among Chinese college students, which is consistent with the results of domestic and international studies (Boehm, 2017; Duan, 2014). Individuals with high levels of mindfulness pay more attention to the perception of the present moment, are more accepting of their own strengths and weaknesses, and more clearly recognize and tend to pursue the value and meaning of their own existence. On the contrary, individuals with lower levels of positive thinking have poorer self-acceptance and a less profound and comprehensive understanding of the self and their own existence (Xu, 2018). This finding is consistent with Frankl’s theory of meaning in life, which mentions that the lack of a sense of meaning in existence motivates people to search for meaning in their lives. Mindfulness refers to the conscious and non-judgmental focusing of attention on the present moment (Kabat-Zinn, 2003), which mainly consists of “self-control of attention” and “orientation to personal experience” (Bishop et al., 2004). Wang and Zhao (2015) suggest that positive thinking can directly and indirectly regulate an individual’s emotions through emotion regulation self-efficacy. Meaning in life is an individual’s subjective experience of the value of his or her existence, and an individual’s subjective experience is closely related to emotions (Zhang, 2022). Many studies have pointed out that an individual’s positive emotion positively predicts life meaning and an individual’s negative emotion negatively predicts life meaning (Ma et al., 2023; Datu, 2016). Xu et al. (2014) concluded that mindfulness significantly moderated the prediction of the effects of perceived stress in daily life on anxiety, fatigue, and overall negative mood.

Limitations and prospects

This study explored the relationship between college students’ physical activity and depression, constructed a chain mediation model, and revealed the intrinsic mechanism of the effect of college students’ physical activity on depression, which is of great theoretical and practical value for understanding the causes of college students’ depression, and also provides a preliminary basis for investigating the causal relationship between these variables. However, this study still has some limitations: first, the cross-sectional design of this study is limited to testing the correlation between variables and cannot infer the causal relationship between variables. Interpretations involving causality or generalization should be avoided or carried out with caution, and future experimental intervention studies with longitudinal follow-up could be conducted to more accurately explain the predictive effect of physical activity on individual depression. Second, the present study only considered the mediating role of mindfulness and sense of meaning in life between physical activity and college students’ depression; in fact, there may be other mediating variables such as life satisfaction, self-efficacy, and positive emotions, etc., and it is necessary to continue to explore the possible mechanisms of the effects of physical activity on college students’ depression in the future. In addition, the convenience sampling method used in this study, the regional characteristics of the participants’ college students, and the unequal proportion of men and women may have affected the generalizability of the findings, and it is necessary for future studies to expand the age range and recruit participants from different schools in different regions to comprehensively explore the trajectory of changes in the effects of physical activity on depression.

Conclusion

The negative predictive effect of physical exercise on depression was significant, and when mediating variables were put in, the direct effect of physical exercise on depression of college students was not significant, and the indirect effect was significant, including two parts of the mediating effect with mindfulness and meaning in life independently and the chain mediating effect with mindfulness and meaning in life as chain mediators.