
==== Front
BMJ Open
BMJ Open
bmjopen
bmjopen
BMJ Open
2044-6055
BMJ Publishing Group BMA House, Tavistock Square, London, WC1H 9JR

39260839
10.1136/bmjopen-2023-079531
bmjopen-2023-079531
Original Research
Public Health
1724
1506
A cross-sectional study of the association between physical activity and depressive symptoms among adolescents in southwest China stratified by parental absence: the mediating role of insomnia and the moderating role of resilience
Zhang Ming 101zhangmingjy0720@163.com

Jiang Jianjun 201jjjun6@163.com

Peng Wei 2hxnyyyg@163.com

Yang Ruixi 1bgm3032@163.com

Liu Qijiao 1liuqj1109@163.com

Li Shiying 3shiyinglipku@126.com

http://orcid.org/0000-0002-8825-0527
Li Yuchen 45liyuchen1991421@163.com

http://orcid.org/0009-0004-0214-2800
Liu Qiaolan 1liuqiaol@scu.edu.cn

1 Department of Health Behavior and Social Medicine, West China School of Public Health and West China Fourth Hospital, Research Center for Palliative Care, West China-PUMC C.C. Chen Institute of Health, Sichuan University West China School of Public Health, Chengdu, Sichuan, China
2 Department of Palliative Care, West China School of Public Health and West China Fourth Hospital, Research Center for Palliative Care, West China-PUMC C.C. Chen Institute of Health, Sichuan University West China School of Public Health, Chengdu, Sichuan, China
3 Department of Sociology and Psychology, Sichuan University School of Public Administration, Chengdu, Sichuan, China
4 Mental Health Center, Sichuan University, Chendu, Sichuan, China
5 Department of Medical Epidemiology and Biostatistics, Karolinska Institute, Stockholm, Sweden
Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.

None declared.

Professor; liuqiaol@scu.edu.cn
MZ and JJ contributed equally.

MZ and JJ are joint first authors.

2024
10 9 2024
14 9 e07953105 9 2023
21 8 2024
Copyright © Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.
2024
https://creativecommons.org/licenses/by-nc/4.0/ This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

Abstract

Objectives

This study explored the mechanisms by which physical activity was associated with depressive symptoms in multi-ethnic (Han, Yi and Tibetan) adolescents in southwest China. The mediating role of insomnia in the association of physical activity with depressive symptoms, the moderating role of resilience in this mediation model and the moderating role of parental absence in the moderated mediation model were also examined.

Design

A cross-sectional survey.

Setting

In southwest China (Sichuan Province and Tibet Autonomous Region).

Participants

3195 adolescents from a school-based survey conducted between April and October 2020.

Methods

There were 3143 valid samples in this study (47.2% males with mean age=12.88±1.68 years). Structural equation models were developed to estimate the direct and mediating effect, and the moderating effect. Multigroup comparison was performed to examine the differences and similarities of the moderated mediation model across three parental absence subgroups: (1) both parents present, (2) one parent absent and (3) both parents absent.

Results

As hypothesised, physical activity was significantly and positively associated with the reduction of depressive symptoms in adolescents. Insomnia partially mediated the effect of physical activity on depressive symptoms. In addition, resilience moderated the direct and indirect effects of physical activity (through insomnia) on depressive symptoms. Finally, the multigroup comparison indicated the moderating effect of parental absence on the moderated mediation model.

Conclusions

Physical activity was associated with alleviating insomnia symptoms among adolescents, thus correlating with the improvement of their depressive symptoms. Resilience was associated with enhancing the beneficial effects of physical activity, further improving depressive symptoms among adolescents, especially those with both absent parents. It is evident that physical activity interventions should be further incorporated into public health programmes to foster the physical and mental health of left-behind adolescents in southwest China.

adolescent
depression & mood disorders
sports medicine
sleep medicine
mental health
developmental neurology & neurodisability
Social Science Training Fund 2021skzx-pt74 http://dx.doi.org/10.13039/501100012226 Fundamental Research Funds for the Central Universities skqy201212 http://dx.doi.org/10.13039/501100001809 National Natural Science Foundation of China 82273745 The funders had no role in the design and implementation of the study, statistical analysis, interpretation of the data or decision to submit the manuscript for publication.
==== Body
pmcSTRENGTHS AND LIMITATIONS OF THIS STUDY

While previous studies have often divided Chinese adolescent groups by left-behind status, this study subdivided them according to parental absence, providing more targeted guidance and support for improving adolescents’ mental health.

This study used a cross-sectional survey, so it is difficult to determine the causal associations among study variables.

This study classified parental absence into three categories: both parents present, one parent absent and both parents absent; however, it has been suggested that father absence and mother absence may have different outcomes on adolescents’ mental health.

The data in this study came from a multi-ethnic, underdeveloped region in southwest China, therefore, caution is needed when generalising the study results to other regional adolescent populations.

Introduction

According to the definition by WHO, adolescence typically refers to the period between the ages of 10 and 19 years.1 Transitioning from childhood to adolescence, individuals grow up while facing more and more stressful life events, which often leads to mental health problems such as depression. Some studies have shown that the prevalence of depression/depressive symptoms in adolescents increases substantially from adolescence onwards, influenced by factors such as increased social understanding and self-awareness.2 Therefore, it can be seen that adolescence is an important period for the mental health development of adolescents. Compared with adult depression, adolescent depression can be more difficult to treat and prone to relapse.3 In recent years, the prevalence of adolescent depression has continued to grow. The 2020 Report on National Mental Health Development in China pointed out that the prevalence of depression among Chinese adolescents was 24.6%, and the prevalence of severe depression was 7.4%.4 Depression has a high comorbidity with anxiety and stress symptoms, and has serious implications for mental health in adulthood.3 5 The issue of adolescent depression has received widespread attention from scholars and policy makers in related fields.

In China, in order to obtain better income, a large number of labour force migrated from the economically underdeveloped cities to the developed cities. Relevant surveys indicated that the migrant population in China was approximately 125 million, most of whom were migrant workers.6 Due to policy restrictions as well as limited resources such as housing, education and healthcare in the cities, most migrants left their children behind in the hometowns, and these left-behind children were taken care of by one of their parents, grandparents or relatives. As of 2013, the number of left-behind children in rural China exceeded 61 million and they were mainly concentrated in large labour export provinces such as Sichuan and Henan.7 For adolescents, parental absence is considered as a serious stressful life event that can cause adverse emotions such as depression, anxiety and suicide/self-harm thoughts/actions, and is also intimately associated with mental illness in adulthood.811 In southwest China, where the number of left-behind adolescents is large, it is of great practical importance to investigate the effects of parental absence on adolescent depressive symptoms and to provide scientific intervention options for ameliorating adolescent depression.

It is in this context that we investigated how protective factors (ie, physical activity) can alleviate adolescent depressive symptoms during adolescence. This study can provide the scientific basis for public health programmes to address the healthcare needs of adolescents, especially those who are in economically disadvantaged areas and report parental absence.

Physical activity and depressive symptoms

Active physical activity is a healthy lifestyle. The Guidelines on Physical Activity and Sedentary Behaviour issued by WHO in 2020 recommended that children and adolescents aged 5–17 years should engage in an average of 60 min (1 hour) of moderate-intensity to vigorous-intensity physical activity per day in order to improve physical and mental health and cognitive functions.12 Existing national and international public health guidelines as well as mental health-related studies have shown that organised, moderate-intensity physical activity is significantly associated with the alleviation of depressive symptoms in adolescents.13 14 A European multinational study with a sample size of 11 110 showed that compared with adolescents who did not participate in physical activity or were inactive, the regression coefficient and its 95% CI between physical activity and depressive symptoms among more active adolescents were −1.7 (−2.2 to –1.2) for boys and −0.7 (−1.2 to –0.2) for girls.13 This suggests that active physical activity might have been significantly associated with the alleviation of depressive symptoms in adolescents. Since the exercise intervention therapy proposed by WHO gained international recognition, it has been increasingly used in the treatment of depression in adolescents, and the antidepressant effect of physical activity has been confirmed.15 16 A recent meta-analysis found that moderate-intensity physical activity had a significant antidepressant effect (Hedges’ g=−0.47, 95% CI −0.71 to −0.24).16 Therefore, the present study proposes the hypothesis that physical activity is negatively associated with depressive symptoms in adolescents with parental absence.

The mediating role of insomnia

According to the scientific report published by the Physical Activity Guidelines Advisory Committee in 2018, appropriate physical activity helps to improve sleep quality in adolescents, thus reducing the risk of depression and anxiety.17 Regarding the effect of physical activity on insomnia, a randomised controlled trial confirmed that physical activity can significantly ameliorate insomnia and reduce depression, and in the physical activity intervention group, the mean decrease in Insomnia Severity Index (ISI) score was 4.06±4.99 (p=0.03), and the mean decrease in Beck Depression Inventory score was 4.35±4.44 (p=0.02).18 A meta-analysis showed that adolescents who report high physical activity are more likely to have good sleep, and physical activity was an effective method to prevent and treat insomnia.19 A study of mental health problems among Chinese adolescents during the COVID-19 outbreak showed that higher physical activity was significantly associated with lower risks of insomnia and depressive symptoms.14

Regarding the impact of insomnia on depressive symptoms, a review of insomnia disorders in adolescence revealed that insomnia is common in adolescents and is strongly associated with psychiatric disorders such as depression.20 A comparative study on differences in depressive symptoms between adolescents and adults showed that adolescents with depression were more prone to experience insomnia symptoms compared with adults.21 A review examining the mechanisms of association between insomnia and depression in adolescence indicated that insomnia in adolescents triggers emotional problems such as depression, and insomnia is a precursor to many internalising symptoms and behavioural problems that seriously affect the development of adolescent physical and mental health in the short and long term.22 It follows that intervening in insomnia during adolescence is the effective way to improve adolescents’ mental health, and physical activity can dramatically ameliorate insomnia and depressive symptoms. Therefore, this study proposes the hypothesis that physical activity can mitigate adolescents’ depressive symptoms by reducing insomnia, that is, insomnia mediates the effect between physical activity and depressive symptoms.

The moderating role of resilience

From the Positive Youth Development (PYD) framework proposed in recent years, resilience is considered to be an internal development asset that can help individuals adapt to negative stressors and adversity and maintain good psychological function.23 Research has indicated that there is an interactive relationship among resilience and the behaviours of adolescents, and the environment in which they lived.24 For example, in terms of the protective-reactive model, resilience can buffer the impact of stressors and mitigate the negative effects on mental health outcomes25; in terms of the protective-protective model, resilience as a protective factor enhances the effects of another protective factor on development outcomes of individuals.26 The two mechanisms of the protective models reflect the different roles of resilience as moderators, that is, buffering the adverse effects of risk factors or promoting the positive effects of protective factors in mental health among adolescents.

Both mechanisms of the protective model have been demonstrated in studies of resilience in Chinese adolescents. A study on depressive symptoms in postearthquake adolescents showed that resilience attenuates the negative effects of stressful life events on depressive symptoms. This study used hierarchical regression to introduce control variables and interaction terms into the regression model, the results showed that the interaction between stressors and resilience significantly predicts adolescent depressive symptoms negatively, with β=−0.189, p<0.05.27 A study of adolescents with emotional-behavioural disorders revealed that resilience increases the protective effect of social support on emotional-behavioural problems. In this study, the interaction coefficient between social support and resilience was statistically significant, with β=−0.071, p<0.05, which supports the protective-protective model.28 Therefore, this study proposes the hypothesis that adolescents’ resilience moderates the direct and indirect pathways of the mediation model. That is, high resilience enhances the positive effects of physical activity on insomnia and depressive symptoms, and diminishes the negative effects of insomnia on depressive symptoms, thus further ameliorating the depressive symptoms of adolescents.

The present study

There are still relatively few studies on insomnia in adolescence among left-behind children and its mechanisms of influence. Therefore, this study constructs a moderated mediation model (see online supplemental figure A.1) and tests the following hypotheses. H1: participation in physical activity is negatively associated with depressive symptoms among adolescents in southwest China. H2: insomnia fully or partially mediates the association between physical activity and depressive symptoms, namely, physical activity can alleviate depressive symptoms by ameliorating insomnia (both full mediation and partial mediation are acceptable). H3: resilience moderates the direct and indirect pathways of the mediation model in H2. Specifically, resilience can enhance the beneficial effects of physical activity on adolescent insomnia symptoms, alleviate the detrimental effects of insomnia symptoms on depressive symptoms and strengthen the beneficial effects of physical activity on depressive symptoms. Finally, we propose H4: there are differences in the moderated mediation model hypothesised by H2 and H3 across different parental absence subgroups, that is, both parents present, one parent absent and both parents absent. In summary, the present study explores the mechanism by which physical activity (through the mediating role of insomnia and the moderating role of resilience) affects depressive symptoms in adolescents, especially for those facing parental absence.

Materials and methods

Participants and procedures

From April to October 2020, a cross-sectional survey was conducted among adolescents in the multi-ethnic gathering areas in southwest China including (1) Cangxi County, Guangyuan City, Sichuan Province; (2) Ganluo County, Liangshan Yi Autonomous Prefecture, Sichuan Province and (3) Lhasa City, Tibet Autonomous Region. This study used multistage cluster sampling to select one elementary school and one middle school from each of three locations. Participants were selected based on the WHO’s definition of the age range for adolescence (10–19 years), all fifth-grade and sixth-grade elementary school students as well as all middle school students from the sample schools were included as study subjects.

The investigators in this study were researchers and graduate students in public health and psychology-related fields. All investigators received uniform training before the start of the survey. This study conducted on-site surveys at sample schools. During the survey, investigators were required to provide participants with information about the purpose and content of the survey. Participants were asked to fill out the questionnaire independently, and the investigators were required to provide neutral explanations of the questions asked by the participants to ensure the authenticity of the survey results. At the end of the survey, the investigators used EpiData V.3.1 to perform the double-entry and logic check of the survey data.

Measures

Parental absence

The parental absence was determined by “Who is currently taking care of you?” Select ‘parents’ represented that both parents were present, select ‘father’ or ‘mother’ represented that one parent was absent, and select other options (such as ‘grandparents’, ‘relatives’, etc) represented that both parents were absent.

Physical activity

The physical activity of adolescents was measured by duration, intensity and frequency.29 The scale consists of four items. (1) ‘The average cumulative time of physical activity per day’, using a 4-point scale with 1=‘none’, 2=‘<30 min’, 3=‘30~60 min’ and 4=‘>60 min’. (2) ‘In the past week, the number of days that physical activity exceeded 30 min’, using a 5-point scale with 1=‘0 days’, 2=‘1~2 days’, 3=‘3~4 days’, 4=‘5~6 days’ and 5=‘7 days’. (3) ‘In the past 30 days, the frequency of participating in physical activity’, using a 4-point scale with 1=‘6~7 times per week’, 2=‘3~5 times per week’, 3=‘1~2 times per week’ and 4=“I didn’t participate in physical activity”. (4) ‘In the past 30 days, the cumulative time of per physical activity’, using a 3-point scale with 1=“I didn’t participate in physical activity”, 2=‘<30 min’ and 3=‘≥30 min’. The third item is reverse scored. The scores of the four items are summed and the total score ranges from 4 to 16, with higher score denoting more frequent physical activity. In the past 30 days, adolescents who participated in physical activity ≥3 times per week and accumulated ≥30 min per physical activity were considered to achieve the standard of physical activity. The results of the confirmatory factor analysis of the scale were as follows: χ2/df=2.079, adjusted goodness-of-fit index (AGFI)=0.997, relative fit index (RFI)=0.995, Tucker-Lewis index (TLI)=0.998, root mean square error of approximation (RMSEA)=0.019, standardised root mean square residual (SRMR)=0.005. The Cronbach’s α coefficient of the physical activity composite variable was 0.72, and McDonald’s Omega coefficient was 0.74. The above results indicated that the reliability and validity of the scale were good.

Insomnia

Insomnia is a latent mediating variable, measured by the ISI.30 This scale contains seven items: (1) ‘difficulty falling asleep’, (2) ‘difficulty staying asleep’, (3) ‘problem waking up too early’, (4) “What extent do you consider your sleep problem to interfere with your daily functioning?”, (5) “How noticeable to others do you think your sleeping problem is in terms of impairing the quality of your life?”, (6) “How worried/distressed are you about your current sleep problem?” and (7) “How satisfied/dissatisfied are you with your current sleep pattern?” Responses are scored on a 5-point scale: 0=‘none’ or ‘very satisfied’, 1=‘mild’ or ‘satisfied’, 2=‘moderate’ or ‘not very satisfied’, 3=‘severe’ or ‘dissatisfied’, 4=‘very severe’ or ‘very dissatisfied’. The scores of the seven items are added together and the total score ranges from 0 to 28, with higher score representing more severe insomnia. Insomnia was defined as the total ISI score >7.30 Previous studies have evidenced the good reliability and validity of this scale.31 In the present study, the Cronbach’s α coefficient of the scale was 0.91.

Depressive symptoms

The depressive symptoms in adolescents were measured by the six-item Kutcher Adolescent Depression Scale (KADS-6). The scale comprises six items describing the core symptoms of depression: (1) ‘low mood, depressed, cannot be bothered’, (2) ‘feeling worthless, hopeless’, (3) ‘tired, low in energy, low motivation’, (4) ‘less experience of fun, pleasure’, (5) ‘feeling worried, nervous, panicky’ and (6) ‘suicide/self-harm thoughts/actions’. Responses are scored on a 4-point scale, that is, 0=‘hardly ever’, 1=‘much of the time’, 2=‘most of the time’ and 3=‘all of the time’. The scores of the six items are summed and the total score ranges from 0 to 18, with higher score indicating more severe depressive symptoms. Adolescents with the total KADS-6 score ≥6 are considered to have depressive symptoms.32 Previous studies have demonstrated the good reliability, validity and sensitivity of the KADS-6.33 In this study, the Cronbach’s α coefficient of the scale was 0.92.

Resilience

Resilience is a latent moderating variable, measured by the Connor-Davidson Resilience Scale (CD-RISC) developed by Connor and Davidson.34 The scale consists of 25 items such as ‘able to adapt to change’, ‘close and secure relationships’ and ‘can deal with whatever comes’. Responses are scored on a 5-point scale from 0 to 4, with 0=‘not true at all’, 1=‘rarely true’, 2=‘sometimes true’, 3=‘often true’ and 4=‘true nearly all of the time’. An exploratory factor analysis of the CD-RISC was conducted, and resilience was further decomposed into three dimensions of tenacity, strength and optimism.35 In the aforementioned study, the Cronbach’s α coefficients for the overall scale and its three dimensions were 0.91, 0.88, 0.80 and 0.60, while in this study, they were 0.97, 0.96, 0.91 and 0.83, respectively. Additionally, in this study, the average variance extracted (AVE) for the three dimensions were 0.63, 0.57 and 0.56, respectively, and the composite reliability (CR) were 0.96, 0.91 and 0.83, respectively. Based on previous research results (AVE >0.5 and CR >0.7 indicate acceptable reliability and validity),36 37 the factor structure of the scale in this study was reasonable, with good convergent validity and internal consistency for each factor. Previous research has shown that the three-factor CD-RISC demonstrated good reliability and validity in assessing the resilience of Chinese adolescents, with fit indices of χ2/df=12.65, TLI=0.85, comparative fit index (CFI)=0.86, RMSEA=0.06 and ECVI (Expected cross-validation index)=1.22.38 In this study, the fit indices for the scale were χ2/df=18.92, CFI=0.92, TLI=0.92, IFI (Incremental fit index)=0.92, RFI=0.91, NFI (Normed fit index)=0.92, RMSEA=0.07 and ECVI=1.69. These results all indicated that the three-factor CD-RISC had good reliability and validity in this study.

Control variables

In subsequent statistical analyses, demographic characteristics including gender, age and ethnicity were statistically controlled as confounders. Age was used as a continuous variable, while gender (1=male, 2=female) and ethnicity (1=Han, 2=Yi, 3=Tibetan) were dummy coded, with ‘male’ and ‘Han’ as the reference categories. Additionally, this study conducted on-site surveys through face-to-face interviews, ensuring that there were no missing data for the main study variables and control variables.

Data analysis

First, for descriptive statistical analysis, this study reported the mean and SD (denoted as mean±SD), or constituent ratio (denoted as n (%)), of each study variable. Second, the independent samples t-test and χ2 test were conducted to compare the differences in physical activity, insomnia, resilience and parental absence between adolescents with depressive symptoms and those without depressive symptoms. Third, the partial correlation analysis was performed on the study variables after adjusting for gender, age and ethnicity. Fourth, the effects of participation in physical activity on depressive symptoms among adolescents were analysed by constructing a structural equation model (SEM) with latent variables. The unconstrained approach was used to create paired product indicators, which constitute interaction terms indicating the moderating effects of latent variables.39 40 The following indices were used to assess the model fit: the AGFI >0.90, the RFI >0.90, the CFI≈0.95, the TLI≈0.95, the SRMR <0.06 and the RMSEA <0.08.41 Additionally, it is important to note that although there are stricter standards, in practical applications, CFI and TLI ≥0.90 are still widely accepted as indicators of a good model fit.42 To test the moderated mediation model, this study used the bias-corrected percentile method with 5000 bootstrap samples. Last but not least, we carried out the multigroup comparison to explore the differences and similarities of the moderated mediation model across different parental absence subgroups. All statistical analyses were performed using SPSS V.24.0 (IBM, Armonk, New York, USA) and Amos V.24.0 (IBM). All significance levels of analyses were defined as p≤0.05 (two-tailed).

Patient and public involvement

Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.

Results

A total of 3195 adolescents participated in the survey. After removing incomplete questionnaires, 3143 adolescents were included in this study, with a mean age of 12.88±1.68 years. Among them, 1483 (47.2%) were male and 1660 (52.8%) were female. There were 1606 (51.1%) Han, 836 (26.6%) Yi and 701 (22.3%) Tibetan participants. A total of 1889 (60.1%) reported that both parents were present, 729 (23.2%) reported that one parent was absent and 525 (16.7%) reported that both parents were absent. 2267 (72.1%) did not achieve the physical activity standard, while 876 (27.9%) achieved the physical activity standard. 1196 (38.1%) had insomnia symptoms, whereas 1947 (61.9%) did not have insomnia symptoms. The average total resilience score was 56.576±24.331, and the mean scores for the three dimensions—tenacity, strength and optimism—were 29.386±13.332, 18.539±7.946 and 8.651±4.172, respectively, as detailed in table 1.

Table 1 Comparison of adolescents with depressive symptoms and those without depressive symptoms

Variable	Total sample (n=3143)	No depressive symptoms (n=2288)	Depressive symptoms (n=855)	t/X2	P value	
(x-±SD)/n (%)	(x-±SD)/n (%)	(x-±SD)/n (%)	
Age	12.883±1.680	12.704±1.676	13.360±1.597	10.111	<0.001	
Gender				0.038	0.872	
 Male	1483 (47.2)	1082 (47.3)	401 (46.9)			
 Female	1660 (52.8)	1206 (52.7)	454 (53.1)			
Ethnicity				140.854	<0.001	
 Han	1606 (51.1)	1316 (57.5)	290 (33.9)			
 Yi	836 (26.6)	516 (22.6)	320 (37.4)			
 Tibetan	701 (22.3)	456 (19.9)	245 (28.7)			
Physical activity				23.565	<0.001	
 Achievement of standard	876 (27.9)	692 (30.2)	184 (21.5)			
 Below standard	2267 (72.1)	1596 (69.8)	671 (78.5)			
Insomnia				722.790	<0.001	
 No insomnia	1947 (61.9)	1743 (76.2)	204 (23.9)			
 Insomnia	1196 (38.1)	545 (23.8)	651 (76.1)			
Resilience	56.576±24.331	58.280±25.541	52.016±20.061	−7.205	<0.001	
 Tenacity*	29.386±13.332	30.262±13.889	27.042±11.394	−6.627	<0.001	
 Strength*	18.539±7.946	19.112±8.329	17.005±6.580	−7.406	<0.001	
 Optimism*	8.651±4.172	8.906±4.347	7.970±3.577	−6.145	<0.001	
Parental absence				12.662	0.002	
 Both parents present	1889 (60.1)	1343 (58.7)	546 (63.9)			
 One parent absent	729 (23.2)	568 (24.8)	161 (18.8)			
 Both parents absent	525 (16.7)	377 (16.5)	148 (17.3)			
* Tenacity, strength and optimism are the three subscales of resilience.

Common method bias

This study used a self-administered questionnaire for the survey, which may lead to common method bias. To mitigate its effects, in terms of procedural remedies, the questionnaire used in this study contained reverse-coded items and we emphasised to the participants that the items had no standard answers. In terms of statistical remedies, a single unmeasured latent method factor was used to test the common method bias.43 We constructed a single latent factor for all items from the entire scale. If the fit indices of the new model did not change significantly compared with the original model (eg, the increase in GFI and NFI did not exceed 0.1 and the decrease in RMSEA did not exceed 0.05), it indicated that there was no serious common method bias.44 In this study, there were no significant changes in the fit indices of the model after the addition of the method factor (ΔTLI=0.028, ΔCFI=0.030 and ΔRMSEA=0.010), indicating no serious common method bias.

Preliminary analysis

Table 1 reports descriptive statistical results and comparisons of study variables grouped by depressive symptoms (possible absence of depressive symptoms and possible presence of depressive symptoms). The results showed that all variables except gender were significantly different in the two subgroups of adolescents with and without depressive symptoms. Adolescents with older age, ethnic minorities (Yi and Tibetan), substandard physical activity, insomnia, lower resilience and reported both absent parents were more likely to have depressive symptoms.

Additionally, this study also analysed the descriptive statistics and comparison results of study variables grouped by parental absence status (both parents present, one parent absent and both parents absent), as detailed in online supplemental table A.1. The results showed that, except for gender and insomnia, all variables showed significant differences across the subgroups of adolescents with different parental absence statuses. Adolescents with absent parents were more likely to be Han and to achieve the physical activity standard. Adolescents with both parents present and both absent were older and were more likely to have depressive symptoms compared with those with one parent absent. The resilience and its dimensions of adolescents with both parents absent were significantly lower than those with both parents present and one parent absent.

Table 2 presents the results of the partial correlation analysis of the study variables after adjusting for gender, age and ethnicity. The results indicated that physical activity was negatively correlated with insomnia (r=−0.098, p<0.001) and depressive symptoms (r=−0.111, p<0.001), and positively correlated with resilience (r=0.249, p<0.001). Insomnia was positively correlated with depressive symptoms (r=0.593, p<0.001) and negatively correlated with resilience (r=−0.059, p<0.01). Resilience appeared negatively associated with depressive symptoms (r=−0.100, p<0.001).

Table 2 Descriptive statistics and partial correlation analysis among variables (n=3143)

Variable	x-±SD	1	2	3	4	
Physical activity	9.948±2.479	1				
Insomnia	6.637±6.262	−0.098***	1			
Depressive symptoms	3.442±4.281	−0.111***	0.593***	1		
Resilience	56.576±24.331	0.249***	−0.059**	−0.100***	1	
**pP<0.01 (two-tailed), ***p***p<0.001 (two-tailed), adjusting for gender, age and ethnicity.

From the results above, it could be seen that although the partial correlation results were significant, the correlation strength between insomnia and positive variables (such as physical activity and resilience) was relatively weak, and the correlation strength between resilience and depressive symptoms was also relatively weak. One possible reason is that although physical activity is generally associated with improved sleep quality, its impact on sleep in adolescents may not have been as pronounced as in adults, and the mechanisms by which physical activity affect adolescent sleep patterns are complex. A study has shown that high-intensity physical activity can increase slow-wave sleep but decrease stage 2 sleep in adolescents.45 Resilience typically helps individuals cope with adversity and may have indirectly alleviated depressive symptoms by reducing stress, hence the low correlation strength between them.46 However, as seen in the ‘Introduction’ section, many studies still confirmed the potential associations between insomnia, resilience and other variables. Therefore, this study used insomnia as a mediator and resilience as a moderator, primarily exploring the relationship between physical activity and adolescent depressive symptoms, as well as the potential moderating effects between them.

Testing the mediating effect of insomnia

A mediation model with latent variables was constructed using Amos V.24.0 to test the mediating effect of insomnia. The fit indices of the mediation model were as follows: χ2/df=11.758, AGFI=0.923, RFI=0.931, CFI=0.944, TLI=0.937, SRMR=0.053 and RMSEA=0.059, indicating that the model fits well. The path coefficients showed that all three pathways of the model, namely, from physical activity to insomnia (β=−0.147, t=−6.855, p<0.001), from physical activity to depressive symptoms (β=−0.068, t=−3.971, p<0.001) and from insomnia to depressive symptoms (β=0.644, t=32.931, p<0.001), were statistically significant (see online supplemental table A.2 and figure A.2 for the mediation model and the significance of the path coefficients).

The bootstrap method with 5000 samples was used to test the statistical significance of the mediating effect, and the results are displayed in online supplemental table A.3. The results revealed that the bootstrap 95% CI for the direct and total effects of physical activity on depressive symptoms and the indirect (mediating) effect of insomnia did not include 0, suggesting that insomnia partially mediated the effect between physical activity and depressive symptoms (the mediating effect=−0.095, bootstrap 95% CI −0.123 to −0.067, p<0.001). The mediating effect (−0.095) accounted for 58.2% of the total effect (−0.163). The above results provided strong support for H1 and H2. Specifically, physical activity may directly improve depressive symptoms in adolescents and indirectly improve depressive symptoms by alleviating insomnia symptoms.

Testing the moderating effect of resilience

Figure 1 illustrates the moderating effect of resilience in the above mediation model. The fit indices of the moderated mediation model were as follows: χ2/df=7.203, AGFI=0.933, RFI=0.939, CFI=0.953, TLI=0.947, SRMR=0.048 and RMSEA=0.044, indicating a good fit. The path coefficients of the model and their significance are shown in online supplemental table A.4. The results indicated that resilience partially moderated the mediation model, that is, the pathways from physical activity to insomnia (β=−0.078, t=−3.596, p<0.001) and from physical activity to depressive symptoms (β=−0.036, t=−2.053, p<0.05). Thus, the moderating effect of resilience mainly involved physical activity. The interaction between insomnia and resilience was not significant, which may be related to the weak correlation strength between them, as detailed in ‘Preliminary analysis’ section.

Figure 1 Standardised structural equation models coefficients (n=3143) for the association between physical activity and depressive symptoms among adolescents in southwest China: the mediating role of insomnia and the moderating role of resilience. E1–E4 represent the four items of the physical activity scale, S1–S7 represent the seven items of the Insomnia Severity Index scale, T1–T6 represent the six items of the Kutcher Adolescent Depression Scale. Tenacity, strength and optimism represent the three subscales of resilience. Int1–Int3 represent the indicators of the interaction term between physical activity and resilience. This study also examined the interaction of insomnia and resilience, which is not shown in the figure because the interaction term is not statistically significant. And the pathways from the control variables (ie, gender, age and ethnicity) to depressive symptoms are omitted. *P<0.05 (two-tailed), **p<0.01 (two-tailed), ***p<0.001 (two-tailed).

To further clarify the moderating effect, resilience was divided into high (x-+SD), medium (x-) and low (x-−SD) groups. The results are presented in table 3. As expected, the effect of physical activity on insomnia was statistically significant at a high level of resilience (β=−0.217, p<0.001); the effect diminished but was still statistically significant at a medium level of resilience (β=−0.116, p<0.01) and the effect had no statistical significance at a low level of resilience (β=−0.014, p>0.05). Similarly, the effect of physical activity on depressive symptoms was significant at a high level of resilience (β=−0.099, p<0.01); the effect diminished but remained significant at a medium level of resilience (β=−0.052, p<0.01) and the effect did not have statistical significance at a low level of resilience (β=−0.006, p>0.05). Finally, and more importantly, the mediating effect of insomnia between physical activity and depressive symptoms was statistically significant at a high level of resilience (β=−0.137, p<0.001); the mediating effect diminished but was still significant at a medium level of resilience (β=−0.074, p<0.001) and the mediating effect did not have statistical significance at a low level of resilience (β=−0.009, p>0.05). In other words, the mediating effect varied among the three levels of resilience subgroups, which partially confirmed H3.

Table 3 Testing the moderating effects of resilience and simple slope analysis

Effect/Effect ratio	Path/Effect association	Effect value	Bias-corrected 95% CI	P value	Percentile 95% CI	P value	
	Physical activity→insomnia	
	 At a high level of resilience	−0.217	(−0.306 to to 0.133)	<0.001	(−0.305 to −0.133)	<0.001	
	 At a medium level of resilience	−0.116	(−0.162 to −0.068)	0.001	(−0.163 to −0.070)	<0.001	
	 At a low level of resilience	−0.014	(−0.095 to 0.064)	0.720	(−0.096 to 0.064)	0.714	
Direct effect	Physical activity→depressive symptoms	
	 At a high level of resilience	−0.099	(−0.156 to −0.046)	0.001	(−0.156 to −0.046)	0.001	
	 At a medium level of resilience	−0.052	(−0.090 to −0.014)	0.009	(−0.091 to −0.015)	0.008	
	 At a low level of resilience	−0.006	(−0.072 to 0.061)	0.867	(−0.073 to 0.060)	0.842	
Indirect (mediating) effect	Physical activity→insomnia→depressive symptoms	
	 At a high level of resilience	−0.137	(−0.197 to −0.083)	<0.001	(−0.196 to −0.082)	<0.001	
	 At a medium level of resilience	−0.074	(−0.104 to −0.044)	<0.001	(−0.105 to −0.044)	<0.001	
	 At a low level of resilience	−0.009	(−0.062 to 0.042)	0.715	(−0.062 to 0.042)	0.714	
Total effect	Direct effect+mediating effect	
	 At a high level of resilience	−0.236	(−0.316 to −0.161)	<0.001	(−0.315 to −0.161)	<0.001	
	 At a medium level of resilience	−0.126	(−0.172 to −0.076)	0.001	(−0.174 to −0.079)	<0.001	
	 At a low level of resilience	−0.015	(−0.093 to 0.062)	0.730	(−0.095 to 0.061)	0.709	
Mediating effect ratio	Mediating effect/total effect	
	 At a high level of resilience	0.580	(0.414 to 0.766)	<0.001	(0.412 to 0.761)	<0.001	
	 At a medium level of resilience	0.585	(0.394 to 0.839)	<0.001	(0.393 to 0.836)	<0.001	
	 At a low level of resilience	0.623	(−1.162 to 35.472)	0.213	(−7.073 to 6.967)	0.601	

Multigroup comparison

The present study conducted the multigroup comparison to examine the differences and similarities of the moderated mediation model among different parental absence subgroups. Based on the results of the model adaptation parameters and invariance test, it was known that except for the measurement weights model and the structural residuals model, the p values of the invariance test for the structural weights model, the structural covariances model and the measurement residuals model were all <0.05. This indicated that there might have been differences in the model among different groups. However, this is not the sole criterion for testing. In this study, the absolute values of the changes in the model fit indices were all <0.05, which also demonstrated good model adaptability. Thus, the model could be considered to be simultaneously adapted to adolescents with different parental absence status (results are shown in online supplemental table A.5.1, online supplemental table A.5.2 and table A.6).

As shown in table 4, compared with adolescents with both parents present, the resilience of adolescents with parental absence had no significant moderating effect on the pathways from physical activity to insomnia and from physical activity to depressive symptoms. Compared with adolescents with both parents absent, the pathway from physical activity to depressive symptoms had no statistical significance in adolescents with both parents present or one parent absent. In addition, the pathway from physical activity to insomnia had no statistical significance in adolescents with both parents absent, but their resilience moderated the pathway from insomnia to depressive symptoms. Further analysis found that as the level of resilience increased, the predictive effect of insomnia on depressive symptoms decreased (see online supplemental table A.7 for results). And importantly, for adolescents with both parents absent, the absolute value of the path coefficient from physical activity to depressive symptoms was significantly higher than for those with both parents present (p<0.05); the absolute value of the path coefficient from the interaction term of insomnia and resilience to depressive symptoms was significantly higher than for those with both parents present (p<0.05) or one parent absent (p<0.05). The above results partially confirmed H4.

Table 4 Path coefficients and critical ratios for multigroup comparison

Path	Both parents present (n=1889)†	One parent absent (n=729)‡	Both parents absent (n=525)§	Critical ratio/p value	
Subgroup I compares with subgroup II	Subgroup I compares with subgroup III	Subgroup II compares with subgroup III	
Physical activity→insomnia	−0.125***	−0.168***	−0.033	−1.014/0.311	1.077/0.281	1.634/0.102	
Insomnia→depressive symptoms	0.612***	0.670***	0.677***	0.605/0.545	−0.244/0.807	−0.706/0.480	
Physical activity→depressive symptoms	−0.023	−0.058	−0.129**	−0.825/0.409	−2.235*/0.025	−1.356/0.175	
Physical activity×resilience→insomnia	−0.097***	−0.038	−0.004	0.868/0.385	1.117/0.264	0.424/0.672	
Insomnia×resilience→depressive symptoms	0.011	0.006	−0.093*	−0.131/0.896	−2.398*/0.016	−2.017*/0.044	
Physical activity×resilience→depressive symptoms	−0.062**	0.006	0.002	1.491/0.136	1.134/0.257	−0.066/0.947	
*P<0.05 (two-tailed), **p<0.01 (two-tailed), ***p<0.001 (two-tailed).

†The subgroup of adolescents with both parents present is noted as subgroup I.

‡The subgroup of adolescents with one parent absent is noted as subgroup II.

§The subgroup of adolescents with both parents absent is noted as subgroup III.

Discussion

Through the construction of the moderated mediation model, this study explored the effect mechanism of physical activity on depressive symptoms among multi-ethnic (Han, Yi and Tibetan) adolescents in southwest China. For adolescents reporting both parents absent and those with moderate to high resilience levels, participation in physical activity serves as a protective factor against depressive symptoms. However, for adolescents reporting at least one parent present and those with low resilience levels, further exploration and validation are needed to understand this effect in more populations. Insomnia partially mediates the relationship between physical activity and depressive symptoms. Moreover, participation in physical activity further ameliorates insomnia and depressive symptoms by enhancing development assets (ie, resilience) in adolescents. Next, we highlight noteworthy findings.

Physical activity was negatively associated with depressive symptoms (H1). In other words, participation in physical activity may be positively correlated with the alleviation of depressive symptoms in adolescents, which was consistent with previous studies.13 14 16 Participation in organised, moderate-to-vigorous intensity, high-frequency and long-duration physical activity was effective in reducing depressive symptoms in adolescents.12 15 However, on entering adolescence, adolescents face a substantial increase in academic and psychological stress accompanied by more sedentary behaviour and less physical activity.47 48 It has been shown that the current global rate of physical inactivity among school-aged adolescents is approximately 80%, and the proportion of adolescents with physical inactivity is gradually increasing worldwide.49 The results of this study also presented a trend of decreasing physical activity among adolescents as they aged. It is evident that engaging adolescents in physical activity actively in the school setting may help promote the mental health development of adolescents in southwest China.

Insomnia partially mediated the effect of physical activity on depressive symptoms after controlling for sociodemographic factors (H2). This implied that, besides its direct effects, participation in physical activity was negatively correlated with the exacerbation of insomnia symptoms in adolescents, which in turn was positively correlated with the exacerbation of depressive symptoms. The results of our study exemplify a possible mechanism by which physical activity modified depressive symptoms and highlight the important impact of sleep problems on physical and mental health among adolescents. Insomnia is a very common sleep disorder in adolescents. Insomnia is strongly associated with depressive symptoms and anxiety and may also predict the development of current and even future internalising symptoms in adolescents, making it a public health issue of great concern.20 22 However, there are still relatively few studies on insomnia in adolescence, especially on its effect mechanisms. In view of the fact that adolescents are more likely to suffer from insomnia as a body dysrhythmia compared with adults,21 investigating the role of physical activity as a protective factor for the amelioration of insomnia symptoms would help to enrich the literature related to the effect mechanisms of insomnia in adolescence.

Third, resilience partially moderated the mediation model (H3). As the level of resilience among adolescents increased, the negative association between physical activity and insomnia as well as depressive symptoms was significantly enhanced. This finding strongly supported the role of resilience as a moderator in promoting protective factors of mental health, that is, the protective-protective model.26 Notably, according to the sport-based PYD theory, physical activity contributes to individual development assets such as resilience and self-efficacy, which in turn enables adolescents to maintain positive growth even under stressful life events.24 Therefore, enhancing physical activity could, to some extent, increase the positive impact of the interaction between physical activity and resilience on mental health and produce more significant effects on ameliorating depressive symptoms in adolescents. It follows that strengthening internal development assets (eg, resilience) through physical activity may be an intervention strategy to promote the healthy growth of adolescents.

Last but not least, the results of the multigroup comparison revealed that the moderated mediation model in H2 and H3 had slightly different operational mechanisms across the three parental absence subgroups (H4). For adolescents reporting both parents absent, participation in physical activity may be positively correlated with the decrease in their depressive symptoms. The possible reason for this result was that school-aged adolescents spend most of their time in the school environment despite the chronic lack of parental care, and supportive school activities (eg, school-organised physical activity) could effectively compensate for the lack of family support and reduce the psychological distress caused by parental absence.50 On the pathways from physical activity to insomnia and from physical activity to depressive symptoms, the moderating effect of resilience was significant in adolescents with both parents present, but not in those with parental absence. According to cumulative situational risk theory, adolescents with parental absence are more likely to be exposed to multiple risk factors that attenuate the positive effects of resilience on insomnia and depressive symptoms.51 Based on previous research, through organised physical activity, in-school adolescents with parental absence could gain support and belonging (eg, the increase in resilience), which in turn alleviated depressive symptoms caused by exposure to risky situations.24 On the pathway from insomnia to depressive symptoms, the moderating effect of resilience was statistically significant among adolescents with both parents absent. This was consistent with the protective-reactive model theory that resilience as a protective factor could buffer the effect of insomnia on depressive symptoms.26 The reason for this may be that adolescents with both parents absent are more likely to have insomnia problems compared with their peers, thus highlighting the role of resilience as a protective factor may mitigate the effect of insomnia on depressive symptoms, and this possibility was confirmed by previous studies.52

In summary, actively organising physical activity may be an intervention for implementing primary preventive healthcare in adolescents' mental health. As the important setting for the growth of adolescents, schools should create a supportive atmosphere to enhance physical activity and promote the development of social skills and psychological assets. In addition, schools and related institutions should focus on the impact of sleep problems on depressive symptoms among adolescents and extend routine health behaviours and mental health monitoring to the campus. This can be targeted to improve the physical and mental health of adolescents, especially for those confronting risky situations such as parental absence.

Limitations

Despite the theoretical and practical implications of this study, there are the following limitations. (1) This study used a cross-sectional survey, so it is difficult to determine the causal associations among study variables, and there is a possibility of reverse causality among the current study variables. In future studies, we propose to use a longitudinal cohort for follow-up. Longitudinal studies would offer better insights into causality and enhance the interpretation of results by capturing changes in variables over time, allowing for the examination of temporal sequencing and minimising the potential for reverse causality. (2) We classified parental absence into three categories: both parents present, one parent absent and both parents absent. However, it has been suggested that father absence and mother absence may have different outcomes on adolescents’ mental health.11 53 54 In the future, we should consider further subdividing the absence of one parent into absent fathers and absent mothers to explore the differences and similarities between the genders of parental caregiving for adolescents. This will contribute to a more comprehensive understanding of the influence of family environment on adolescent mental health, provide more targeted intervention measures to meet the needs of adolescents of different genders, thereby making the research results more practically meaningful. (3) Cultural, economic and social environmental differences across regions may lead to regional variations in the impact on the study variables. The data for this study came from a multi-ethnic, underdeveloped area in southwest China, so differences compared with adolescent populations in other parts of China cannot be ruled out. Additionally, our use of survey methods to collect data may not be easily comprehensible to groups with lower educational levels (such as ethnic minority adolescents), leading to lower response rates and questionnaire quality among these groups. In summary, the influence of sample selection bias cannot be excluded in this study. Therefore, caution is needed when generalising the study results to other regional adolescent populations. Future research could improve the accuracy and generalisability of the results by expanding the sample scope and combining quantitative surveys with qualitative interviews.

Conclusions

As a protective factor, active participation in organised physical activity can help adolescents develop psychosocial assets in the school environment, regulate changes in body rhythms and thus improve their mental health. It is especially important for left-behind adolescents. Schools, research institutions and government agencies should collaborate to promote the implementation and dissemination of adolescent public health programmes that use physical activity as an intervention to enhance the physical and mental health of adolescents in the less developed, multi-ethnic regions of southwest China.

supplementary material

10.1136/bmjopen-2023-079531 online supplemental file 1

Acknowledgements

The authors would like to thank all the funders and workers of this study, as well as all the respondents who provided data. The authors are very grateful to the editors and reviewers for their review and suggestions on this paper.

Data availability statement

Data are available on reasonable request.

Review Process File
10 09 2024

Funding: This investigation was supported by funding from (1) National Natural Science Foundation of China (grant number: 82273745), (2) Social Science Training Fund (grant number: 2021skzx-pt74) and (3) Fundamental Research Funds for the Central Universities (grant number: skqy201212).

Prepublication history and additional supplemental material for this paper are available online. To view these files, please visit the journal online (https://doi.org/10.1136/bmjopen-2023-079531).

Provenance and peer review: Not commissioned; externally peer reviewed.

Patient consent for publication: Not applicable.

Ethics approval: This study was approved by the Medical Ethical Committee of Sichuan University (No. K2018086). All procedures of this study were conducted in accordance with the Helsinki Declaration. Participants gave informed consent to participate in the study before taking part.

Patient and public involvement: Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
==== Refs
References

1 Boyce E Rights H Boyce WJAHP, Science Application of the convention on the rights of the child to adolescent health policy 2009 249
2 Thapar A Collishaw S Pine DS et al Depression in adolescence The Lancet 2012 379 1056 67 10.1016/S0140-6736(11)60871-4
3 Dunn V Goodyer IM Longitudinal investigation into childhood- and adolescence-onset depression: psychiatric outcome in early adulthood Br J Psychiatry 2006 188 216 22 10.1192/bjp.188.3.216 16507961
4 Fu XL Zhang K Report on national mental health development in China (2019-2020) (in Chinese) 2021
5 Feiss R Dolinger SB Merritt M et al A Systematic Review and Meta-Analysis of School-Based Stress, Anxiety, and Depression Prevention Programs for Adolescents J Youth Adolesc 2019 48 1668 85 10.1007/s10964-019-01085-0 31346924
6 Main Data of the Seventh National Population Census (in Chinese) Chin Stat 2021 5 4 5
7 Research Group of All-China Women’s Federation National study on the situation of left-behind children in rural areas and urban and rural migrant children (in Chinese) Chin Women's Mov 2013 30 4
8 Liu Z Li X Ge X Left too early: the effects of age at separation from parents on Chinese rural children’s symptoms of anxiety and depression Am J Public Health 2009 99 2049 54 10.2105/AJPH.2008.150474 19762669
9 Li X Coid JW Tang W et al Sustained effects of left-behind experience during childhood on mental health in Chinese university undergraduates Eur Child Adolesc Psychiatry 2021 30 1949 57 10.1007/s00787-020-01666-6 33113025
10 Inoue Y Fukunaga A Stickley A et al Association between parental absence during childhood and depressive symptoms in adulthood in rural Vietnam J Affect Disord 2022 311 479 85 10.1016/j.jad.2022.05.102 35598745
11 Fu M Xue Y Zhou W et al Parental absence predicts suicide ideation through emotional disorders PLoS One 2017 12 e0188823 10.1371/journal.pone.0188823 29216233
12 Bull FC Al-Ansari SS Biddle S et al World Health Organization 2020 guidelines on physical activity and sedentary behaviour Br J Sports Med 2020 54 1451 62 10.1136/bjsports-2020-102955 33239350
13 McMahon EM Corcoran P O’Regan G et al Physical activity in European adolescents and associations with anxiety, depression and well-being Eur Child Adolesc Psychiatry 2017 26 111 22 10.1007/s00787-016-0875-9 27277894
14 Chi X Liang K Chen S-T et al Mental health problems among Chinese adolescents during the COVID-19: The importance of nutrition and physical activity Int J Clin Health Psychol 2021 21 100218 10.1016/j.ijchp.2020.100218 33391373
15 Bailey AP Hetrick SE Rosenbaum S et al Treating depression with physical activity in adolescents and young adults: a systematic review and meta-analysis of randomised controlled trials Psychol Med 2018 48 1068 83 10.1017/S0033291717002653 28994355
16 Oberste M Medele M Javelle F et al Physical Activity for the Treatment of Adolescent Depression: A Systematic Review and Meta-Analysis Front Physiol 2020 11 185 10.3389/fphys.2020.00185 32265725
17 Piercy KL Troiano RP Ballard RM et al The Physical Activity Guidelines for Americans JAMA 2018 320 2020 8 10.1001/jama.2018.14854 30418471
18 Hartescu I Morgan K Stevinson CD Increased physical activity improves sleep and mood outcomes in inactive people with insomnia: a randomized controlled trial J Sleep Res 2015 24 526 34 10.1111/jsr.12297 25903450
19 Lang C Kalak N Brand S et al The relationship between physical activity and sleep from mid adolescence to early adulthood. A systematic review of methodological approaches and meta-analysis Sleep Med Rev 2016 28 32 45 10.1016/j.smrv.2015.07.004 26447947
20 de Zambotti M Goldstone A Colrain IM et al Insomnia disorder in adolescence: Diagnosis, impact, and treatment Sleep Med Rev 2018 39 12 24 10.1016/j.smrv.2017.06.009 28974427
21 Rice F Riglin L Lomax T et al Adolescent and adult differences in major depression symptom profiles J Affect Disord 2019 243 175 81 10.1016/j.jad.2018.09.015 30243197
22 Blake MJ Trinder JA Allen NB Mechanisms underlying the association between insomnia, anxiety, and depression in adolescence: Implications for behavioral sleep interventions Clin Psychol Rev 2018 63 25 40 10.1016/j.cpr.2018.05.006 29879564
23 Masten AS Invited commentary: Resilience and positive youth development frameworks in developmental science J Youth Adolesc 2014 43 1018 24 10.1007/s10964-014-0118-7 24723048
24 Ho FKW Louie LHT Wong WH-S et al A Sports-Based Youth Development Program, Teen Mental Health, and Physical Fitness: An RCT Pediatrics 2017 140 e20171543 10.1542/peds.2017-1543 28951440
25 Masten AS Resilience in children threatened by extreme adversity: frameworks for research, practice, and translational synergy Dev Psychopathol 2011 23 493 506 10.1017/S0954579411000198 23786691
26 Fergus S Zimmerman MA Adolescent resilience: a framework for understanding healthy development in the face of risk Annu Rev Public Health 2005 26 399 419 10.1146/annurev.publhealth.26.021304.144357 15760295
27 Zhu Q Fan F Zheng Y et al Moderating and mediating effects of resilience between negative life events and depression symptoms among adolescents following the 2008 Wenchuan Earthquake in China (in Chinese) Chin J Clin Psychol 2012 20 514 7
28 Sun S Guan Y Qin Y et al Social support and emotional-behavioral problems: resilience as a mediator and moderator (in Chinese) Chin J Clin Psychol 2013 21 114 8
29 Liang D Stress levels of students in higher education and their relationship with physical activity (in Chinese) Chin Ment Health J 1994 5 6
30 Morin CM Insomnia: Psychological Assessment and Management New York, NY, US Guilford Press 1993
31 Morin CM Belleville G Bélanger L et al The Insomnia Severity Index: psychometric indicators to detect insomnia cases and evaluate treatment response Sleep 2011 34 601 8 10.1093/sleep/34.5.601 21532953
32 Xu J Wang Y Tang W Risk Factors of Post-traumatic Stress and Depressive Disorders in Longmenshan Adolescents After the 2013 Lushan Earthquake Community Ment Health J 2019 55 497 506 10.1007/s10597-018-0256-6 29511996
33 LeBlanc JC Almudevar A Brooks SJ et al Screening for adolescent depression: comparison of the Kutcher Adolescent Depression Scale with the Beck depression inventory J Child Adolesc Psychopharmacol 2002 12 113 26 10.1089/104454602760219153 12188980
34 Connor KM Davidson JRT Development of a new resilience scale: the Connor-Davidson Resilience Scale (CD-RISC) Depress Anxiety 2003 18 76 82 10.1002/da.10113 12964174
35 Yu X Zhang J Factor analysis and psychometric evaluation of the Connor-Davidson Resilience Scale (CD-RISC) with Chinese people Soc Behav Pers 2007 35 19 30 10.2224/sbp.2007.35.1.19
36 Fornell C Larcker DF Evaluating Structural Equation Models with Unobservable Variables and Measurement Error J Market Res 1981 18 39 10.2307/3151312
37 Hair J Babin W Babin B et al Multivariate Data Analysis with Readings, 7th Ed Englewood Cliffs, NJ Prentice Hall 2010
38 Yu X-N Lau JTF Mak WWS et al Factor structure and psychometric properties of the Connor-Davidson Resilience Scale among Chinese adolescents Compr Psychiatry 2011 52 218 24 10.1016/j.comppsych.2010.05.010 21295229
39 Marsh HW Wen Z Hau KT Structural equation models of latent interactions: evaluation of alternative estimation strategies and indicator construction Psychol Methods 2004 9 275 300 10.1037/1082-989X.9.3.275 15355150
40 Wen Z Wu Y Evolution and simplification of the approaches to estimating structural equation models with latent interaction (in Chinese) Adv Psychol Sci 2010 18 1306 13
41 Hu L Bentler PM Cutoff criteria for fit indexes in covariance structure analysis: Conventional criteria versus new alternatives Struct Equ Modeling 1999 6 1 55 10.1080/10705519909540118
42 Bentler PM Comparative fit indexes in structural models Psychol Bull 1990 107 238 46 10.1037//0033-2909.107.2.238 2320703
43 Podsakoff PM MacKenzie SB Lee J-Y et al Common method biases in behavioral research: a critical review of the literature and recommended remedies J Appl Psychol 2003 88 879 903 10.1037/0021-9010.88.5.879 14516251
44 Wen Z Huang B Tang D Preliminary work for modeling questionnaire data (in Chinese) J Psychol Sci 2018 41 204 10
45 Dworak M Wiater A Alfer D et al Increased slow wave sleep and reduced stage 2 sleep in children depending on exercise intensity Sleep Med 2008 9 266 72 10.1016/j.sleep.2007.04.017 17644426
46 Tugade MM Fredrickson BL Resilient individuals use positive emotions to bounce back from negative emotional experiences J Pers Soc Psychol 2004 86 320 33 10.1037/0022-3514.86.2.320 14769087
47 Chmelík F Frömel K Groffik D et al Does Vigorous Physical Activity Contribute to Adolescent Life Satisfaction? Int J Environ Res Public Health 2021 18 2236 10.3390/ijerph18052236 33668269
48 Fuentealba-Urra S Rubio-Rivera A González-Carrasco M et al The Moderating Role of Sociodemographic Factors in the Relationship between Physical Activity and Subjective Well-Being in Chilean Children and Adolescents Int J Environ Res Public Health 2021 18 11190 10.3390/ijerph182111190 34769709
49 Sallis JF Bull F Guthold R et al Progress in physical activity over the Olympic quadrennium The Lancet 2016 388 1325 36 10.1016/S0140-6736(16)30581-5
50 Lai S Zhou J Xu X et al Subjective well-being among AIDS orphans in southwest China: the role of school connectedness, peer support, and resilience BMC Psychiatry 2022 22 197 10.1186/s12888-022-03833-2 35303813
51 Evans GW Li D Whipple SS Cumulative risk and child development Psychol Bull 2013 139 1342 96 10.1037/a0031808 23566018
52 Zhou Y-M Zhao C-X Qi Y-J et al Emotional and Behavioral Problems of Left-Behind Children in Impoverished Rural China: A Comparative Cross-Sectional Study of Fourth-Grade Children J Adolesc Health 2020 67 S48 54 10.1016/j.jadohealth.2020.06.016 33246533
53 Chen M Sun X Chen Q et al Parental Migration, Children’s Safety and Psychological Adjustment in Rural China: A Meta-Analysis Trauma Violence Abuse 2020 21 113 22 10.1177/1524838017744768 29333970
54 Mao M Zang L Zhang H The Effects of Parental Absence on Children Development: Evidence from Left-Behind Children in China Int J Environ Res Public Health 2020 17 6770 10.3390/ijerph17186770 32957472
