Abstract

Purpose

In recent years, the problem of college student suicide has become more and more serious, and depression has become the main root cause, triggering the attention of colleges and universities at home and abroad. Based on the burnout theory, this study explores the intrinsic connection between physical activity, depression and academic burnout. Through two questionnaire surveys, the cross-sectional relationship between physical activity level, depression and academic burnout was analyzed. A parallel mediation model was developed to compare the mediating effects of physical activity and depression. Meanwhile, physical activity grading was quantified to assess the effect on improving academic burnout and depression.

Methods

A longitudinal study was conducted utilizing a physical education classroom with questionnaires measuring students' physical activity, school burnout, and depression. The test was administered twice, at the beginning and end of the semester, with 305 valid participants each time. SPSS 27.0 was used to process the data, perform descriptive statistics and correlation analyses, and explore the relationships between variables. Multiple linear regression was used to analyze the mediating relationships and lagged effects of physical activity, school burnout, and depression. Finally, the amount of physical activity was graded to examine the effects of different intensities on school burnout and depression.

Results

In a cross-sectional study at two time points, school burnout would serve as a mediator between college students' physical activity depression. We compared the lagged mediating effects of the two groups and found that school burnout (Time 2) had a more significant effect as a mediator. Finally, we graded the amount of physical activity according to the scale and found that only high-intensity physical activity affected depression (Time 2) through school burnout (Time 2).

Conclusion

There was temporal stability between physical activity, depression, and school burnout among college students. School burnout fully mediated the relationship between physical activity and depression at different time points and acted as a fully lagged mediator. School burnout at time 2 mediated the relationship between physical activity and depression more than school burnout at time 1. High-intensity physical activity was more effective in reducing depression and school burnout.

Background

In recent years, a number of college student suicides have been occurring in many domestic and overseas colleges and universities, and the root cause of these suicides is depression. Depression, which is characterized by persistent low mood, slow thinking, cognitive dysfunction and loss of willpower, has become a major factor affecting the mental health of college students. Data from the China National Mental Health Development Report (2019鈥�2020) show that the detection rate of depression among college students in China is as high as 24.6%, of which the detection rate of mild depression is 17.2% and that of severe depression is 7.4%. Patients with major depression are more prone to suicidal behavior [1], so it is particularly important to do a good job of prevention and control, intervention and treatment, and explore the factors related to the emergence of depression. At present, depression in college students is closely linked to the social environment and psychological factors [2]. At this stage, the main means of controlling depression is medication, however, medications have certain side effects and long-term medication is obviously not a long-term solution. Therefore, it is extremely important to find effective ways to de-stress, prevent or reduce school burnout and depressive symptoms.

The concept of school burnout is derived from Maslach's theory of job burnout [3], which refers to the response to school-related stress [4]. It is characterized by school work-induced fatigue, cynicism and belief in underachievement [3, 5, 6]. Students suffering from school burnout show lack of interest in school life, frequent absenteeism, prolonged tardiness and irresponsible behavior [7]. Patients with burnout exhibit lower levels of self-efficacy [8] and sleep worse [9], with a gradual decline in cognitive function [10]. As a result, the ability to work and learn declines [11], and college students with chronic school burnout display a lack of interest in school life, frequent absences, chronic tardiness, and irresponsible behavior [7]. At present, more than 50% of teenagers in China suffer from learning burnout [12], 37.8% of college students have lost interest in learning [13], and the truancy rate is as high as 67.81% [14]. burnout is regarded as the core causative factor in many theories of depression [15], although differentiated from the phenomenon of depression, but in fact there is a close correlation between the two in terms of symptoms, and there are a variety of depressive symptoms in the group of burnout patients. In terms of clinical symptoms, up to 90% of burnout patients (n鈥�=鈥�67) fulfill the criteria for depression [16]. In a study that directly compared the depressive symptoms of a group of burnout patients (n鈥�=鈥�46) and a group of clinically depressed outpatients (n鈥�=鈥�46) in a DSM-based methodology, the results showed no significant differences in symptoms [17]. Leiter and Durup [18] suggest that burnout encompasses components such as the energy loss and chronic fatigue, which is considered to be typical symptoms of depression. Depression, on the other hand, has been shown to be the ultimate symptom of burnout [19], and in addition, the correlation between burnout and depression has been confirmed [20]. Burnout has been shown to lead to depression, and as the level of burnout increases, the stronger its correlation with depression [21], mental health will also progressively deteriorate [22], and these studies provide strong evidence that there is a strong link between burnout and depression.

As a method to reduce school burnout with low cost and no side effects, physical activity may be one of the most effective of the interventions for learning burnout [23]. Zhou Xihua [24] conducted a 2-month exercise intervention with 105 college students with high levels of learning burnout. The experimental results showed that physical activity could significantly reduce the level of study burnout among college students. In addition, after the exercise intervention, the cultural scores of the intervention groups were all improved [25]. In their daily study life, college students can reduce the level of study burnout by regularly participating in various kinds of sports activities to improve their physical and psychological health [26]. And badminton exercise has a significant effect on the treatment of anxiety and burnout symptoms [27]. Some studies have even shown that the most significant psychological health effect is achieved by sustained moderate-intensity physical activity for more than 6 months [28]. This is because regular participation in physical activity can help individuals psychologically disengage from work, thereby reducing the risk of long-term stress reactions, including adverse emotions such as burnout, and by engaging in regular physical activity, individuals can not only enhance their ability to cope with psychological stress, but also recover more quickly from stress, thereby effectively reducing the risk of burnout. In addition, exercise promotes the secretion and regulation of a variety of neurotransmitters and neuromodulators, further improving mood states and increasing energy expenditure. These neurotransmitters and neuromodulators can affect the cognitive, emotional and behavioral aspects of an individual to help them better cope with academic stress and burnout. Therefore, reducing burnout through physical activity is a very effective method that not only has the advantages of low cost and no side effects, but also promotes the physical and mental health of individuals.

Physical activity (PA) interventions as an alternative or complementary treatment has significant advantages for college students [29, 30], with physical activity significantly reducing their levels of state anxiety, depression, tension, and psychological disorders, while increasing energy and enjoyment [31]. According to a large number of experimental studies, physical activity has a significant effect in improving depression, not only in the disease population, general college students and ethnic minority college students, but even in patients with major depressive disorder this effect has been observed [32, 33]. Research also shows that the improvement effect of physical activity on depression seems to be independent of the sport program, and the antidepressant effect of ball games, gymnastics, yoga and strength training are well reflected [34, 35]. Existing research shows that the time, frequency and period of exercise may be the key factors affecting the effect of physical activity on depression, and there is a significant correlation between the three elements of exercise and depression [36]. In studies on depressed mice, the molecular and cellular mechanisms and channels of action of physical activity against depression have been found to synergistically promote the improvement of depression by improving the functions of the hippocampus, prefrontal cortex and amygdala, and regulating the contents of neurotrophic factors, serotonin and dopamine and their receptor activities, and some of these mechanisms have also been corroborated to a certain extent in studies on human beings. However, the therapeutic effects of the relevant drugs developed using these mechanisms in the clinic are lagging behind, and there is still a need to further strengthen the research on the relevant mechanisms [37, 38].

Although there have been empirical studies that have demonstrated a relationship between physical activity (PA) and depression and school burnout, there have been few studies linking the three. In addition, there is still uncertainty regarding whether school burnout mediates the relationship between physical activity and depression. In order to accurately identify the mechanisms and pathways through which these variables work, we must first conduct in-depth research on how these variables work. Only then can we effectively find scientific and correct interventions for school burnout in order to help adolescents grow up healthy and contribute to society. At the same time, such a study will also help to further improve the relevant theories of school burnout and promote the development of theoretical research in this field. In addition, based on previous research results, we can clearly see that physical activity has a delayed effect in the treatment of depression [39]. Currently, the research at this stage is mainly in the cross-sectional study of the above three variables and does not classify physical activity according to the intensity, therefore, the purpose of this study is to explore and test whether physical activity can have a delayed therapeutic compensatory effect on school burnout and depression in a scientific manner by using two advanced methods, namely, longitudinal lag and structural equation modeling analysis. Meanwhile, the relationship between depression and school burnout was explored based on Katariina's [40] bivariate crossover delayed follow-up study. The results of the study indicated that school burnout was a significant predictor of depressive symptoms and that there was a cumulative cycle. In summary, we need to further investigate whether school burnout mediates the relationship between physical activity and depression and whether this mediation is delayed. These findings not only help us better understand the positive effects of physical activity on depression, but also provide new perspectives and possible approaches to the treatment of depression.

The present study

Although previous studies have focused on the positive effects of physical activity on physical and mental health, in-depth exploration of the complex relationship between physical activity, school burnout, and depression is still lacking. This study aims at filling the gap in current research by analyzing the relationship between these three in depth based on the burnout theory. Through this study, we expect to gain a deeper understanding of the intrinsic links between physical activity, school burnout, and depression, thereby providing theoretical support for the development of more effective health interventions. Specifically, the objectives of this study are threefold: first, we will investigate whether there is a significant correlation between physical activity, school burnout and depression; second, we will investigate whether school burnout mediates the relationship between physical activity and depression in these two cross-sectional time points, and further test the mediating effect of school burnout(Time 1 and Time 2) in these two time points, and explore which mediation effect is more significant by comparing parallel mediation; finally, we will quantitatively grade physical activity to explore the extent to which different intensities of physical activity affect school burnout and depression.Based on the literature review, we proposed the following hypotheses:

• Hypothesis 1 Physical activity is negatively associated with depression among college students.

• Hypothesis 2 School burnout in college students will be a mediator between physical activity and depression.

• Hypothesis 3 The lagged school burnout mediator had a more significant effect on the relationship between physical activity and depression among college students compared to the contemporaneous school burnout mediator effect.

• Hypothesis 4 College students' participation in high-intensity physical activity will have a greater impact on school burnout and depression.

Materials and methods

Participants

The study utilized a longitudinal survey [41] research design and the sampling was done by using the whole cluster sampling method [42]. A total of 305 male students from 10 different teaching classes were selected for the survey. The subjects (aged between 18鈥�21 years with a mean age of 18.54 years), who were from the College of Materials, College of Management, College of Urban Construction, College of Chemical Engineering, College of Mechanical Automation, and the School of Computer Science. These students were recruited during a mandatory physical education class at the beginning of the fall semester and had no specific motivation to participate in this study.In order to increase the motivation of participants, we ensure that each participant has a clear understanding of the objectives of the program, their role, and the desired outcomes. This helps them to see their value in the process and become more engaged.In order to control for socially expected answers, participants were encouraged to answer the questions as truthfully as possible and were assured that they could withdraw from the study at any time and that their answers would not affect their grades. The study was approved by the Institutional Review Board of Wuhan University of Science and Technology (WUST) and the institute at the college, and participants' consent was obtained before the study. After obtaining participants' consent, the researchers collected data through offline classroom surveys. The first test was administered shortly after the start of the first semester of the 2023 academic year (October 2023.10), and the second test was administered prior to the first semester final exams (December 2023.12). There were 305 valid participants for the first test and 305 valid participants for the second test. We spaced these time points far enough apart to capture changes and align with course and exam schedules.

Measuring tools

School burnout

School burnout was measured by using the school burnout questionnaire called "MBI-SS" [3]conducted. The scale consists of 14 items, including measures of exhaustion from schoolwork (e.g., "Studying makes me feel physically and mentally exhausted"), cynicism about attitudes toward school (e.g., "I have become less and less interested in studying since I entered college"), and feelings of low self-efficacy at school (e.g., "I can effectively solve problems that arise in my studies"). The questionnaire utilized a Likert-type 7-point scale from 1 (completely disagree) to 7 (completely agree). Items on exhaustion and cynicism were scored positively and items on feelings of low self-efficacy were scored negatively to calculate overall burnout levels. Higher scores indicate higher levels of burnout. For the purposes of this paper, the scale has a Cronbach's of 0.874 and 0.907 for time1-2.

Depression

Depressive symptoms were measured using the Chinese version of the Patient Health Questionnaire-9(PHQ-9) scale [43] to determine the presence of depressive symptoms and their severity. According to the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, the PHQ-9 contains nine items reflecting major depressive symptoms. Subjects were first asked, "In the past two weeks, how many times have you been bothered by any of the following?" They are then asked to rate on a Likert-type scale from 0 (not at all) to 3 (almost every day) the degree to which each item's statement corresponds to their experience.The PHQ-9 produces a single score, ranging from 0 to 27, by summing the responses to each item.The severity of depressive symptoms has been categorized into five levels by Cronk et al.: minimal (0鈥�4), mild (5鈥�9), moderate (10鈥�14), severe (15鈥�19) and severe (20鈥�27). The scale has a Cronbach's of 0.827 and 0.834 for time 1鈥�2.

Leisure-time physical activity (LTPA)

In the measurement of physical activity, the Godin-Shephard [44] Leisure time physical activity(LTPA) questionnaire was used to quantify long-term physical activity in college students. The title of the questionnaire explicitly prompted students that they needed to report the frequency of exercise activities that they performed during their free time, lasting longer than 30 min, during the past week. Students were asked to provide feedback on statements related to the intensity of their exercise, which included 1. high-intensity LTPA, such as running, field hockey, competitive aerobics, soccer, basketball, and high-intensity swimming, which causes a rapid heart rate; 2. moderate-intensity LTPA, such as brisk walking, tennis, cycling, volleyball, badminton, and strength exercises, or easy swimming and table tennis, which do not exhaust students; 3. light-intensity LTPA, such as walking at a brisk pace, or easy swimming and ping-pong, which do not cause students to exhaustion; After each statement, students were asked to fill in the number of times per week they participated in the physical activity corresponding to that intensity. The reliability of this questionnaire has been validated in a university setting in China using objective measures such as calculated acceleration and maximum oxygen consumption (VO2MAX) [45]. The reliability of this questionnaire showed good properties [46]. High-intensity, moderate-intensity, and light-intensity LTPA activities were expressed by multiplying the weekly frequency by the corresponding Metabolic Equivalent of Task(MET) scores: 9, 5, and 3. These values (i.e., 9 for vigorous; 5 for moderate; and 3 for light LTPA) indicate the MET values for activities of different intensity [44].

Statistical analysis

SPSS 27.0 was used as a data processing tool in this study. In the questionnaire, we conducted detailed descriptive statistics and correlation analysis of the raw data to determine the relationship between the variables. Descriptive statistics are used to describe the basic characteristics of data, such as the mean, standard deviation, and median. Through descriptive statistics, we can initially understand the distribution of the data and the relationship between the variables. In this study, descriptive statistics help us to understand the basic situation of the research object and provide a basis for subsequent in-depth analysis.Correlation analysis is used to explore the strength and direction of the relationship between two or more variables. By calculating the correlation coefficient, we can understand the degree of association between variables and how changes in one variable affect changes in another. In this study, correlation analysis helped us to reveal the correlation between the variables and provided a basis for the subsequent regression analysis.Regression analysis is used to further explore the relationship between variables and to determine the extent to which one or more of the independent variables affects the dependent variable.

Utilizing multiple linear regression, we delved into the mediating relationships among the quantity of physical activity, school burnout, and depression across various cross-sections. Additionally, we aimed to investigate whether there existed a delayed impact of physical activity on school burnout and depression. Subsequently, we categorized the amount of physical activity to identify the optimal intensity that most effectively influenced school burnout and depression.

Results

Descriptive analysis

Based on the data in Table听1, we can clearly observe a positive correlation between physical activity (Time 1) and physical activity (Time 2)(r鈥�=鈥�0.293, P鈥�<鈥�0.001). At the same time, there are significant negative correlations between physical activity (Time 1) and school burnout (Time 1)(r鈥�=鈥�-0.282, P鈥�<鈥�0.001), school burnout (Time 2)(r鈥�=鈥�-0.184, P鈥�<鈥�0.001), depression (Time 1)(r鈥�=鈥�-0.284, P鈥�<鈥�0.001) and depression (Time 2)(r鈥�=鈥�-0.150, P鈥�<鈥�0.001). There was a significant negative correlation between physical activity (time 2) and school burnout (time 1) (r鈥�=鈥�-0.205, P鈥�<鈥�0.001), school burnout (time 2) (r鈥�=鈥�-0.298, P鈥�<鈥�0.001), depression (time 1) (r鈥�=鈥�-0.143, P鈥�<鈥�0.05) and depression (time 2) (r鈥�=鈥�-0.249, P鈥�<鈥�0.001).These negative correlations suggest that when a person's physical activity decreases, their levels of school burnout and depression may increase accordingly. Furthermore, this negative correlation may have a negative impact on students long afterward. Additionally, as seen in Table听1, there is a significant positive correlation between school burnout and depressive symptoms. This means that when a person's level of school burnout increases, their depressive symptoms may increase accordingly. At the same time, this aggravation may last for a long period of time. In summary, physical activity was significantly and negatively associated with school burnout and depression both at (Time 1) and (Time 2). Thus,maintaining appropriate levels of physical activity may help reduce school burnout and depressive symptoms and positively impact students' long-term mental health.

Table听1 Statistics of pearson correlation coefficient

Analysis of the mediating effect of school burnout (Time 1) between physical activity (Time 1) and depression (Time 1)

Regression analysis of physical activity (Time 1), school burnout (Time 1), and depression (Time 1)

The results showed (see Table听2) that the negative effect of physical activity (Time 1) on school burnout (Time 1)(尾鈥�=鈥�-0.282,t鈥�=鈥�-5.117,P鈥�<鈥�0.001)was significant, and the negative effect of physical activity (Time 1) on depression (Time 1)(尾鈥�=鈥�-0.284,t鈥�=鈥�-5.157,P鈥�<鈥�0.001) was significant and remained significant after the mediating variable [school burnout (Time 1)](尾鈥�=鈥�-0.106,t鈥�=鈥�-2.375,P鈥�&濒迟;鈥�0.05).

Table听2 Regression analysis of the multiple mediation model

Mediating effects test for school burnout (Time 1) between physical activity (Time 1) and depression (Time 1)

We tested the validation of the model in Fig.听1 using Model 4 in the SPSS macro program, which was designed to test hypothesis 2. The results are presented in Table听3. From Tables听2 and听3 we can see the mediating effects of the above variables.This study then tested the mediating effect of school burnout (Time 1) between physical activity (Time 1) and depression (Time 1). The results showed that the Total effect of this model was significant (effect value of -0.042, within the 95% Bootstrap confidence interval, ranging from -0.058 to -0.026), and that this interval, did not contain the value "0", so the Total effect was significant. And with the inclusion of the mediator variable, the Direct prediction of depression (Time 1) by physical activity (Time 1) was also significant(effect value of -0.016, within the 95% Bootstrap confidence interval, ranging from -0.028 to -0.003). The mediating effect of physical activity on depression through school burnout was -0.026, which ranged from -0.375 to -0.017 within the 95% Bootstrap confidence interval, an interval that does not include the value "0," suggesting that the mediating effect was significant. Due to the significant overall effect of the model, the direct effect after adding mediating variables is also significant, and the mediating effect is significant. Therefore, the model is a partial mediating model, in which school burnout (time 1) plays a partial meditating role in this relationship.

Fig.听1

Model of mediating effect of school burnout (Time 1) between physical activity (Time 1) and depression (Time 1). Notes: PA鈥�=鈥塒hysical Activity, SB鈥�=鈥塖chool Burnout, DEPR鈥�=鈥塪epression, T1鈥�=鈥塗ime 1

Table听3 Test results of bootstrap mediation effect

Analysis of the mediating effect of school burnout (Time 2) between physical activity (Time 2) and depression (Time 2)

Regression analysis of physical activity (Time 2), school burnout (Time 2), and depression (Time 2)

The results showed (see Table听4) that the negative effect of physical activity (Time 2) on school burnout (Time 2)(尾鈥�=鈥�-0.298,t鈥�=鈥�-5.437,P鈥�<鈥�0.001)was significant, and the negative effect of physical activity (Time 2) on depression (Time 2)(尾鈥�=鈥�-0.249,t鈥�=鈥�-4.437,P鈥�<鈥�0.001) was significant and with the addition of the mediating [school burnout (Time 2)], the direct effect is no longer significant (尾鈥�=鈥�-0.662,t鈥�=鈥�-1.42,P鈥�&驳迟;鈥�0.05).

Table听4 Regression analysis of the multiple mediation model

Mediating effects test for school burnout (Time 2) between physical activity (Time 2) and depression (Time 2)

We tested the validation of the model in Fig.听2 using Model 4 in the SPSS macro program, which was designed to test hypothesis 2, This study then tested the mediating effect of school burnout (Time 2) between physical activity (Time 2) and depression (Time 2). Table 5 showed the results that the Total effect of this model was significant (effect value of -0.044, within the 95% Bootstrap confidence interval, ranging from -0.063 to -0.025), and that this interval, which did not include the value "0", made the Total effect significant. However, the Direct prediction of depression (Time 2) by physical activity (Time 2) was not significant with the inclusion of the mediator variable (effect value of -0.012, ranging from -0.028 to 0.005 within the 95% Bootstrap confidence interval). In contrast, the mediating effect value of physical activity on depression through school burnout was -0.032, which ranged from -0.048 to -0.017 within the 95% Bootstrap confidence interval, which did not include the value "0," indicating that the mediating effect was significant. Because the Total effect of this model is significant and the Direct effect is not significant after adding the mediator variable, but the mediator effect is significant, this model is a fully mediated model, which means that school burnout (Time 2) plays a fully mediated role in this relationship.

Fig.听2

Model of mediating effect of school burnout (Time 2) between physical activity (Time 2) and depression (Time 2). Notes: PA鈥�=鈥塒hysical Activity, SB鈥�=鈥塖chool Burnout, DEPR鈥�=鈥塪epression, T1鈥�=鈥塗ime 1, T2鈥�=鈥塗ime 2

Table听5 Test results of bootstrap mediation effect

Analysis of the lagged mediating effect of school burnout between physical activity and depression

Regression analysis of physical activity (Time 1), school burnout (Time 1), and depression (Time 2)

The results showed (see Table听6) that the negative effect of physical activity (Time 1) on school burnout (Time 1)(尾鈥�=鈥�-0.282,t鈥�=鈥�-5.117,P鈥�<鈥�0.01)was significant, and the negative effect of physical activity (Time 1) on depression (Time 2)(尾鈥�=鈥�-0.150,t鈥�=鈥�-2.647,P鈥�<鈥�0.001) was significant and with the addition of the mediating [school burnout (Time 1)], the direct effect is no longer significant (尾鈥�=鈥�-0.057,t鈥�=鈥�-1.007,P鈥�&驳迟;鈥�0.05).

Table听6 Regression analysis of the multiple mediation model

Regression analysis of physical activity (Time 1), school burnout (Time 2), and depression (Time 2)

The results showed (see Table听7) that the negative effect of physical activity (Time 1) on school burnout (Time 2)(尾鈥�=鈥�-0.184,t鈥�=鈥�-3.257,P鈥�<鈥�0.001)was significant, and the negative effect of physical activity (Time 1) on depression (Time 2)(尾鈥�=鈥�-0.150,t鈥�=鈥�-2.647,P鈥�<鈥�0.001) was significant and remained significant after the mediating variable [school burnout (Time 2)](尾鈥�=鈥�-0.035,t鈥�=鈥�-0.775,P鈥�&驳迟;鈥�0.001).

Table听7 Regression analysis of the multiple mediation model

Mediating effects test for school burnout (Time 1) and school burnout(Time 2) between physical activity (Time 1) and depression (Time 1)

We tested the validity of the models shown in Figs.听3 and 4 using Model 4 in the SPSS macro program, which was the basis for testing Hypothesis 3. This study then tested the mediating effect of school burnout (Time 1) between physical activity (Time 1) and depression (Time 2). Table 8 shows that the total effect of the model was significant (effect value of -0.024, within the 95% Bootstrap Confidence Interval ranging from -0.042 to-0.006) and that the interval did not contain a "0" value, thus the total effect was significant. The direct predictive effect of physical activity (Time 1) on depression (Time 2) was no longer significant with the addition of the mediator variable (effect value of -0.006, ranging from -0.020 to 0.009 within the 95% Bootstrap confidence interval). Thus school burnout (Time 1) acted as a partial mediator effect between physical activity (Time 1) and depression (Time 2), and this model is a fully mediating effect model.

Fig.听3

Model of mediating effect of school burnout (Time 1) between physical activity (Time 1) and depression (Time 2). Notes: PA鈥�=鈥塒hysical Activity, SB鈥�=鈥塖chool Burnout, DEPR鈥�=鈥塪epression, T1鈥�=鈥塗ime 1, T2鈥�=鈥塗ime 2

Fig.听4

Model of mediating effect of school burnout (Time 2) between physical activity (Time 1) and depression (Time 2). Notes: PA鈥�=鈥塒hysical Activity, SB鈥�=鈥塖chool Burnout, DEPR鈥�=鈥塪epression, T1鈥�=鈥塗ime 1, T2鈥�=鈥塗ime 2

Table听8 Test results of bootstrap mediation effect

Table 9 showed the results that the mediating effect value of physical activity (Time 1) on depression (Time 2) through school burnout (Time 2) was -0.024, which ranged from -0.042 to -0.006 within the 95% Bootstrap confidence interval, which did not include the value "0," indicating that the mediating effect was significant. Because the Total effect of this model is significant and the Direct effect is not significant after adding the mediator variable, but the mediator effect is significant, this model is a fully mediated model, which means that school burnout (Time 2) plays a fully mediated role in this relationship.

Table听9 Test results of bootstrap mediation effect

Analysis of parallel mediated effects of school burnout (Time 2) and school burnout (Time 1) between physical activity (Time 1) and depression (Time 2)

Parallel mediating effects test for school burnout (Time 1) and school burnout (Time 2) between physical activity (Time 1) and depression (Time 2)

We tested the validation of the model in Fig.听5 using Model 4 in the SPSS macro program, which was designed to test hypothesis 3.In previous studies, we have shown that school burnout plays a mediating role in physical activity and depression, based on the same measuring times.听School burnout also has a lag mediating effect between physical activity and depression, which is based on between the two measuring times. To explore this more deeply, we further investigated which mediating effect was more significantly influenced by physical activity. Based on the parallel mediation model in Table听10, we found that school burnout (Time 2) mediated particularly well between physical activity and depression,the mediating effect value of physical activity(Time 1) on depression(Time 2) through school burnout was -0.018,which ranged from-0.031 to -0.007 within the 95% Bootstrap confidence interval, which did not include the value "0," indicating that the mediating effect was significant. This suggests that the lagged mediating effect of physical activity on school burnout(Time 2) is more significant compared to its contemporaneous school burnout (time1) meditating effect.

Fig.听5

Model of mediating effect of school burnout (Time 2) and school burnout (Time 1) between physical activity (Time 2) and depression (Time 2). Notes: PA鈥�=鈥塒hysical Activity, SB鈥�=鈥塖chool Burnout, DEPR鈥�=鈥塪epression, T1鈥�=鈥塗ime 1, T2鈥�=鈥塗ime 2

Table听10 Parallel mediating effects of school burnout (Time 2) and school burnout (Time 1) between physical activity (Time 1) and depression (Time 2)

Mediating effects test for school burnout(Time 2) between physical activity at different intensities (Time 1) and depression (Time 2)

After finding that school burnout (time 2) had the most significant effect on physical activity and depression, we sought to explore which intensity of physical activity had the best effect on depression in the Fig.听5 model by grading the amount of physical activity according to the LTPA questionnaire. So we transformed the different physical activity intensities (high, medium and low) into dummy variables and studied the mediator variable school burnout (time 2) and the dependent variable depression (time 2) as continuous variables. The results of the analysis are detailed in Table听11:

Table听11 Analysis of the lagged mediating effect of school burnout (Time 2) between physical activity of varying intensity (Time 1) and depression (Time 2)

The mediating effect of school burnout on the effects of different intensities of physical activity on and depression was examined using a bias-corrected bootstrapping test (5,000 extracts) using the process plug-in of the SPSS statistical software. In the mediation effect analysis model of this study, the independent variable of different intensity of physical activity (high, medium, and low) was coded as a dummy variable, and the mediating variable of school burnout and the dependent variable of depression were continuous variables.

As seen in the Table听11, the Direct effect of high intensity physical activity on depression was not significant when the control group was used as a reference. However, when school burnout (Time 2) was introduced as a mediator variable, the mediated effect value of high-intensity physical activity on depression (Time 2) was -2.490. This effect value was within the 95% Bootstrap confidence interval, ranging from (-3.655 to -1.394), and the interval did not contain the value "0", indicating a significant effect., indicating a significant mediating effect. This indicates that the effect of high-intensity physical activity on depression is largely mediated through the effect of school burnout, and this model is a fully mediated model. On the other hand, the mediation effect of moderate-intensity physical activity was -0.963, with a 95% confidence interval of (-2.346,0.451), which included the value "0", indicating that the mediation effect was not significant. Meanwhile, the Direct effect of moderate-intensity physical activity on depression was 1.858, with a confidence interval of (-0.019, 3.735), which also included the value of "0", indicating that this pathway was not valid. Taken together, it can be concluded that high-intensity physical activity is effective in improving school burnout, thereby further reducing depressive symptoms. This provides a strong scientific basis for schools and students to encourage them to actively participate in high-intensity physical activities to improve mental health.

Discussion

Our study explored the relationship between physical activity, school burnout, and depression among college students through a cross-sectional and longitudinal design. Results indicated that physical activity was positively associated with depression in the cross-sectional study, while school burnout mediated the relationship between physical activity and depression. In addition, school burnout acted as a lag mediator between physical activity and depression, and this lag effect was stronger than the mediating effect of school burnout (time 1). Finally, we quantitatively graded physical activity on the lagged mediating effect model and found that high-intensity physical activity could better reduce depression symptoms by affecting college students' school burnout compared with moderate- and low-intensity physical activity.

According to Hypothesis 1, college students' participation in physical activity can significantly reduce their level of school burnout and have a significant negative impact on depressive symptoms, which is consistent with the results of previous studies [47], and in addition, physical activity, as an intervention without side effects, can promote the physical and mental health of individuals. The results of many empirical studies have shown that physical activity increases cerebral blood flow and maximal oxygen consumption, decreases muscle tone, and activates the endogenous cannabinoid system, among other effects, which contributes to the improvement of an individual's psychological state and make people feel physically and mentally well-being. Therefore, physical activity plays an important role in combating burnout and depression. To summarize, by participating in physical activity, college students can reduce their school burnout and thus reduce depressive symptoms. Not only does burnout predict new cases of depressive symptoms, but in turn, depression predicts new cases of burnout [48], and burnout and depression may "go hand in hand [49]." The results of the present study also confirmed that burnout played a fully mediating role in physical activity and depression at different points in time, confirming the temporal stability of school burnout.

According to Hypothesis 2, at the measurement two months later, we again observed the effects of physical activity on students' school burnout symptoms and depression. This finding is exciting because it further confirms our previous findings that physical activity reduces students' school burnout symptoms and thus affects their depression levels. This effect was stable over time, implying that the effect of physical activity on improving students' mental health was not transient. Instead, this positive impact remained even over a two-month time span. This provides strong evidence to support the inclusion of physical activity in schooling programs to improve students' mental health. In conclusion, our findings suggest that physical activity has a significant role in reducing students' school burnout symptoms and depression and is stable over time. This provides a strong scientific basis for schools and parents to encourage children to participate more in physical activities to promote their physical and mental health.

Based on Hypothesis 3, school burnout at different time points mediates in the pathways of physical activity and depression.According to the data school burnout has a lagged mediating effect in time. This implies that college students can reduce their school burnout by engaging in physical activity, thus reducing their depressive symptoms. Previous studies have not examined these three variables together, so this study attempts to explore these three variables together. First, from Hypothesis 1, we can see that school burnout is positively correlated with depression, and physical activity is significantly negatively correlated with both school burnout and depression, a finding that is also supported by previous research [50]. This study also found that college students' participation in sports activities has a lag effect on their burnout symptoms. A lag effect is the delayed effect of an event in time, which in this case refers to the fact that the effect of physical activity on school burnout becomes more significant after a period of time. By comparing the data from short-term and long-term studies, we found that the lagged effect of physical activity on school burnout is more significant in the long term. This may be due to the fact that physical activity requires a certain amount of time and accumulation to produce a lasting effect, which in turn has a deeper impact on school burnout. That is, college students who frequently participates in physical activity have a lower probability of exacerbating burnout and depressive symptoms over a longer period of time.

According to Hypothesis 3, we found that school burnout played a fully mediating role between physical activity and depression. Specifically, both school burnout Time 1 and school burnout Time 2 at the same time point, they were directly associated with physical activity Time 1 and depression Time 2. This finding provides us with a new perspective on the intrinsic links between the three. Based on this we further compared the related mediation coefficients. The results of the study show that students' burnout improves significantly after 2 months of physical activity. This finding is significant in that it highlights the long-term effects of physical activity in alleviating students' burnout. In addition, our study provides insight into how physical activity reduces student burnout and depressive symptoms through multiple mechanisms. First, physical activity enhances students' physical Fitness and immunity, thereby reducing burnout triggered by physical fatigue. Second, physical activity has a positive effect on students' mental health, effectively reducing anxiety and depression. At the same time, physical activity can also help increase students' social interactions and teamwork opportunities, helping them build healthy interpersonal relationships and further alleviating loneliness and stress.

According to Hypothesis 4, regarding the effects brought about by different levels of physical activity, our analysis showed that there was a significant difference in the level of school burnout between the high, medium, and low physical activity level groups. At the same time, the level of school burnout increases sequentially as the amount of exercise decreases; this is consistent with the results of previous studies [51, 52], as well as the findings that college students' perceived academic stress decreases as the level of physical activity increases, and that the academic stress scores of college students with high and medium levels of physical activity are significantly lower than those of college students [53] with low levels of physical activity.Chekroud [54] also concluded that the amount of physical activity in medium and high levels of physical activity brings the the best mental health benefits. This may stem from the fact that high-intensity physical activity (PA) is more likely to desensitize arousal cues, thereby reducing high levels of stress and anxiety [55], and these studies suggest that high-intensity physical activity has a positive impact on college students' mental health and academic performance. Negative emotions and perceived academic stress are important factors that contribute to school burnout. Therefore the reason for the differences in school burnout among college students with different levels of physical activity may be that participation in more physical activities reduces school burnout on the basis of lowering college students' negative emotions and perceived academic stress, i.e., higher levels of physical activity may be associated with lower school burnout [56]. In conclusion, the results of this study suggest that high-intensity physical activity has a significant impact on the mental health of college students. And it can reduce the risk of depression by reducing school burnout. Therefore, we should encourage college students to actively participate in higher-intensity physical activities to reduce their negative emotions and perceived academic stress, thus reducing the incidence of school burnout. At the same time, we should also focus on other factors that may influence college students' school burnout to provide more comprehensive support for improving their mental health and academic performance.

Implications

For college students, the findings of this study have profound implications. Firstly, it underscores the critical role of physical activity, especially high-intensity physical activity, in promoting mental health and academic performance. Encouraging college students to engage in regular and intense physical activities can help reduce negative emotions, perceived academic stress, and ultimately, school burnout. This can be achieved through promoting physical activities on campus, providing facilities and resources for students to engage in physical activities, and integrating physical activities into the academic curriculum.

Secondly, the results of this study highlight the need for a comprehensive approach to improving the mental health and academic performance of college students. While physical activity is an important factor, it is not the only factor. Other factors such as academic workload, social support, and coping strategies may also play a role in influencing college students' school burnout. Therefore, it is necessary to consider a range of interventions and supports to address these issues comprehensively.

Lastly, the findings of this study also have implications for policymakers and educators. By understanding the relationship between physical activity and mental health outcomes, policymakers can develop policies and strategies to promote physical activity in higher education institutions. Educators can also integrate physical activities into their teaching practices to enhance students' learning experiences and overall well-being. By doing so, we can help college students achieve their full potential and thrive both academically and mentally.

Limitations and future research

The present study was devoted to exploring the lagged effects of physical activity on depressive symptoms and school burnout among Chinese male college students, and revealing the lagged mediating role of school burnout in the relationship between physical activity and depressive symptoms. It was further found that high-intensity physical activity had a more significant effect on alleviating school burnout and thus alleviating depression compared with medium- and low-intensity physical activity. This result provides a valuable reference for preventing or alleviating school burnout and depression symptoms among college students. However, since this study only focused on a sample of male students in a college in central China, there may be some school and gender limitations in the results of the study. In order to enhance the generalizability and applicability of the study, future studies should expand the sample to include a wider range of respondents and introduce covariates such as gender and grade level for control. The next study could also be conducted in the east and west central regions of China, selecting students from different universities, in order to deeply explore the differences in school burnout among college students in different regions and schools. As a next step, the researcher plans to conduct the third questionnaire collection after the spring school year begins and further analyze the trend of subjects' school burnout over time using Mplus's potential growth model. If the data are of analytical value, the cross-lagged model of Mplus will also be used to explore the correlation between these three variables at the three points in time, so as to more accurately reveal the causal relationship between these three variables.

Conclusions

• (1) Physical activity (Time 1) is a negative predictor of depression (Time 1) and school burnout (Time 1) among college students, and school burnout (Time 1) will act as a mediator between the effects of physical activity (Time 1) and depression (Time 1) among college students.This means that if college students are able to maintain regular physical activity, they may be more engaged academically and their depression may be alleviated. On the contrary, if college students lack physical activity, they may feel more tired and frustrated, which may cause them to be more burned out academically, thus further exacerbating their depressive mood.

• (2) Physical activity (Time 2) is a negative predictor of depression (Time 2) and school burnout (Time 2) among college students, and school burnout (Time 2) will act as a mediator between the effects of physical activity (Time 2) and depression (Time 2) among college students.The results of this study reveal the importance of physical activity in the mental health and academic achievement of college students. Over time, college students' depression and school burnout may gradually accumulate, negatively affecting their mental health and academic performance. However, by adhering to physical activity, college students can effectively alleviate these negative emotions and stress, thereby improving their mental health and academic performance.

• (3) Physical activity (Time 1) was a negative predictor of depression (Time 2) and academic burnout (Time 1) in college students, while academic burnout (Time 1) would mediate the effect between physical activity (Time 1) and depression (Time 2) in college students. This phenomenon is explained by the fact that physical activity contributes to the enhancement of students' psychological well-being during the same period of time and reduces school burnout, which in turn reduces the likelihood of subsequent depression.

• (4) Physical activity (Time 1) is a negative predictor of depression (Time 2) and school burnout (Time 2) among college students, and school burnout (Time 2) will act as a mediator between the effects of physical activity (Time 1) and depression (Time 2) among college students.This conclusion finds that physical activities have significant long-term benefits. It can not only instantly reduce students' school burnout and depression, but also effectively prevent the occurrence of these two psychological problems over a longer period of time.

• (5) School burnout (Time 2) has more significant mediating effects in physical activity (Time 1) and depression (Time 2) compared to school burnout (Time 1).And high-intensity physical activity seems to have a more important effect on burnout and depression compared to moderate- and low-intensity physical activity.This means that a student's participation in physical activity at a given point in time may affect their subsequent burnout from school, which in turn may further contribute to the emergence of depressive moods. Second, high-intensity physical activity appeared to have a more significant effect on burnout and depression than moderate- and low-intensity physical activity. This may be due to the fact that high-intensity physical activity is more effective in improving students' physical fitness and psychological well-being, which in turn reduces burnout and depression towards school.