Chain-mediation effect of cognitive flexibility and depression on the relationship between physical activity and insomnia in adolescents

Abstract

Background

Physical activity has positive benefits in promoting the physical and mental health of adolescents. This study focuses on the importance of adolescent mental health issues, exploring the relationship between physical activity and insomnia in adolescents, as well as the mediating roles and pathways of cognitive flexibility and depression.

Methods

A cross-sectional study was conducted using self-reports to collect data on physical activity, insomnia, cognitive flexibility, and depression. A total of 501 valid questionnaires were collected from two middle schools in the western region of Hunan Province.

Results

Physical activity directly and significantly predicted insomnia negatively (β =−0.153, SE = 0.047, p < 0.01). However, the predictive effect of physical activity on insomnia was no longer significant in the indirect effect analysis (β =−0.053, SE = 0.041, p > 0.05). Serial mediation analyses identified significant indirect effects through cognitive flexibility and depression in sequence (β =−0.029, 95% CI [−0.053,−0.011]), accounting for 18.95% of the total effect.

Conclusions

The study strengthens evidence for the associations between adolescent physical activity, insomnia, cognitive flexibility and depression, demonstrating that the beneficial effects of physical activity on insomnia are sequentially mediated through cognitive flexibility and depression. Given the dual benefits of physical activity for both sleep quality and mental health, we recommend implementing targeted physical activity interventions for adolescents, with particular emphasis on activities designed to enhance cognitive flexibility.

Introduction

Physical activity

Physical activity is defined as any bodily movement produced by skeletal muscles that results in energy expenditure [1]. The benefits of physical activity extend across multiple dimensions, including cellular mechanisms [2], physical function [3], psychological well-being [4–6], and genetic development [7]. However, physical inactivity has emerged as a global epidemic [8, 9]. Global data reveal an age-standardized physical inactivity prevalence of 27.5% in 2016 [10]. Adolescents show particularly alarming trends, with 81% classified as physically inactive in 2020 [11]. This rate exhibits a persistent upward trajectory [12]. Insufficient physical activity poses multiple health risks, with studies demonstrating its association with cardiovascular diseases, diabetes, obesity, sleep disorders, psychological problems, and overall mortality [13, 14]. Focusing on adolescents, research has confirmed that insufficient physical activity in this population poses significant risks to obesity, cardiometabolic health, and mental health [15]. Emphasizing the positive benefits of physical activity is crucial for promoting the physical and mental health development of adolescents.

Insomnia

The physical and mental health of adolescents has always been a matter of concern. While insufficient physical activity in adolescents has become a global issue, insomnia disorders have also emerged as a widespread problem in this population. Insomnia is a form of sleep-onset-associated disorder (SOAD) or restricted sleep disorder [16]. According to the diagnostic criteria of the Diagnostic and Statistical Manual of Mental Disorders, 5th edition [17] and other studies [18], the main manifestations of insomnia disorder include difficulty falling asleep and maintaining sleep, with a diagnostic criterion of experiencing these difficulties on ≥ 3 days per week. Insomnia disorder is considered an important independent risk factor for physical and mental health [19]. The prevalence of insomnia disorder is high among adolescents [20], with a study of adolescents aged 16–19 years showing an insomnia prevalence ranging from 13.6 to 23.8% [21]. Insomnia is associated with various psychiatric disorders and is an independent risk factor for adolescent suicide and substance use [20, 22]. Interventions for insomnia disorder include pharmacological treatment and cognitive interventions [23], and physical activity is increasingly recognized as a potential intervention [24, 25]. Studies have shown that physical activity can improve sleep or significantly affect sleep quality [26, 27]. The underlying mechanisms of the relationship between physical activity and insomnia require further exploration.

Mediating role of cognitive flexibility between physical activity and insomnia

Both physical activity and executive function play crucial roles in adolescent mental health development, with strong interconnections between them [28, 29]. A meta-analysis demonstrated significant positive effects of physical activity on executive function in adolescents (g = 0.24; 95% CI [0.09, 0.39]) [30], with supporting electroencephalographic evidence [31]. As one of the three core EF components [32, 33], cognitive flexibility defined as the ability to adapt behavior appropriately to changing environmental demands [34, 35], it shows significant positive associations with various physical activity modalities (P < 0.05) [36]. Recent studies identify complex interconnections between executive function, insomnia, and physical activity [37, 38]. Specifically regarding cognitive flexibility, neuroscientific investigations demonstrate: exercise-induced cognitive interactions [39], significant physical activity-cognition associations [40]. The prefrontal cortex-mediated cognitive flexibility is regulated by dopamine and norepinephrine systems [41], providing neurobiological mechanisms underlying physical activity-cognitive flexibility relationships. Robust evidence supports the cognitive flexibility-insomnia connection [42–45], with studies consistently demonstrating inverse relationships between cognitive flexibility and sleep disturbances [46]. These established relationships warrant further investigation into potential pathways linking physical activity, cognitive flexibility, and insomnia.

Mediating role of depression between physical activity and insomnia

Depression is essentially an emotional disorder, characterized by low mood and loss of interest or pleasure [47]. Adolescence is a period of high risk for the onset of various psychopathologies, including anxiety, depression, obsessive-compulsive disorder, and schizophrenia [29]. Among these, depression has a relatively high prevalence. The prevalence of depression increased by 37% between 2001 and 2020 [48]. Studies have also shown that the prevalence of depression among children and adolescents in China is consistent with the global trend of increasing prevalence [49]. For instance, a study involving 29,626 Chinese children and adolescents reported that the prevalence of depression ranged from 4 to 41%, with an overall prevalence of 19.85% (95% CI: 14.75 − 24.96%) [50]. Physical activity serves as a vital public health intervention for mental disorders, including depression and anxiety [51]. Empirical evidence confirms its dual benefits: reducing depression incidence in general populations [52, 53], alleviating depressive symptoms specifically in adolescents [54–56]. In the physiological explanation of depression, decreased levels of the neurotransmitter serotonin have a significant impact on the manifestations and symptoms of insomnia [57]. Many studies have investigated anxiety and depression as comorbid conditions with insomnia [16, 58]. The correlation between depression and insomnia has been validated and supported by numerous studies [44, 59, 60]. Based on these relationships and the evidence of the correlation between physical activity and insomnia, we can further infer that there is a certain connection between depression, physical activity, and insomnia.

Relationship between cognitive flexibility and depression

In studies on depression, executive functions have been identified as one of the most affected cognitive domains in depression [61]. As a core executive function component, cognitive flexibility directly correlates with depression severity [62]. Enhanced cognitive flexibility predicts two positive outcomes: increased stress resilience [63] and improved mental health status [64]. Cognitive flexibility can predict lower levels of depression [65–67]. In the explanatory mechanisms of the relationship between cognitive flexibility and depression, cognitive flexibility can enhance an individual’s ability to regulate negative emotions and shift their way of thinking, thereby reducing depression levels [68, 69]. In depression interventions based on cognitive restructuring, cognitive flexibility has been proven to be one of the variables in treating depression [64]. Based on the discussions of the relationships among physical activity, cognitive flexibility, depression, and insomnia, we can further investigate the mechanisms underlying the impact of physical activity on insomnia from a more microscopic perspective and clarify the important roles of cognitive flexibility and depression in the relationship between physical activity and insomnia.

Current study

Based on the previous discussions, the following research hypotheses were proposed for this study: H1, there is a significant negative correlation between physical activity and insomnia; H2, cognitive flexibility plays a mediating role between physical activity and insomnia; H3, depression plays a mediating role between physical activity and insomnia; H4, cognitive flexibility and depression exert a chain mediation effect between physical activity and insomnia. Based on this hypothesis, a chain mediation model was developed (see Fig. 1) to investigate the relationship between physical activity and insomnia, as well as the mechanisms by which cognitive flexibility and depression modulate this relationship. This study aims to investigate the positive benefits of physical activity and the complex dynamic relationships among different variables. It attempts to understand the impact of physical activity on insomnia at the mechanistic level and provide more evidence-based support and improvement strategies for interventions targeting adolescent insomnia.

Fig. 1.

Study Model

Participants and methods

Participants

This study employed a cross-sectional survey design, utilizing convenience sampling to distribute questionnaires to two secondary schools in the western region of Hunan Province to collect relevant data. The study meets and passes ethical approval ([2024]98) and meets the basic requirements of the Declaration of Helsinki. All participants were fully informed of the purpose and significance of the study. Informed consent was obtained from both the participants and their guardians. Participants were free to interrupt or withdraw from the study at any time. The survey could be completed in approximately 10 min. After excluding questionnaires with excessively long or short completion times, those with obvious response patterns, and incomplete responses, a total of 501 valid questionnaires were collected (240 boys, 261 girls; 83 only children, 418 non-only children; 436 boarding students, 65 non-boarding students; 377 left-behind children, 124 non-left-behind children). The average age of participants was 15.35 ± 0.541 years.

Measurement tools

Physical activity

Physical activity levels were assessed using the revised Physical Activity Rating Scale (PARS-3) [70]. This scale includes three dimensions: intensity, duration, and frequency. The scoring formula for physical activity level is: Physical Activity Level = Intensity × (Duration − 1) × Frequency. Scores range from 0 to 100, with higher scores indicating higher levels of physical activity. The Cronbach’s α coefficient for this sample was 0.653.

Insomnia

Insomnia was measured using the Athens Insomnia Scale (AIS) [71]. The AIS consists of eight items, scored on a 4-point Likert scale, with total scores ranging from 8 to 32. Higher total scores indicate more severe insomnia. The Cronbach’s α for this scale in the current study was 0.827.

Cognitive flexibility

Cognitive flexibility was assessed using the cognitive flexibility subscale of the Adolescent Executive Function Scale (AEFS) [72]. This subscale comprises eight items, scored on a Likert scale ranging from 1 (often) to 3 (never). The total score of the eight items represents the level of cognitive flexibility, with scores ranging from 8 to 32. Higher scores indicate stronger cognitive flexibility. The Cronbach’s α for this sample was 0.843.

Depression

Depression levels were evaluated using the Depression subscale of the Depression, Anxiety, and Stress Scale (DASS−21), which was originally developed by Lovibond and Lovibond (1995) [73] and later translated and validated for local use by Gong et al. (2010) [74]. The Depression subscale consists of seven items, scored on a 4-point Likert scale ranging from 1 (strongly disagree) to 4 (strongly agree). The total score of the seven items represents the level of depression, with scores ranging from 7 to 28. Higher scores indicate higher levels of depression. The Cronbach’s α for this sample was 0.867.

Data analysis

All statistical analyses were performed using SPSS 26.0. First, Harman’s single-factor test [75] indicated no substantial common method bias (< 40% threshold). Second, raw data were standardized (z-scores) to minimize scaling discrepancies. Descriptive statistics and bivariate correlations were calculated for demographic characteristics and study variables. To test hypotheses, we employed Model 6 of the PROCESS macro v4.1 [76] to examine: direct associations between physical activity and insomnia, serial mediation effects via cognitive flexibility and depression. In this process, we utilized 5,000 bootstrap resampling iterations to assess model fit and estimate the 95% confidence intervals (95% CI), thereby enhancing the robustness of our data analysis, in line with the recommendations of Berkovits et al. [77]. During the analysis, gender and age were controlled as covariates. The significance level was set at 0.05.

Results

Common method Bias test

The common method bias in this study was assessed using the Harman single-factor test. The results indicated the presence of four factors with eigenvalues greater than 1. The first factor accounted for 24.734% of the total variance, which is below the threshold of 40%. This suggests that there is no significant risk of common method bias in this study.

Correlation analysis

As shown in Table 1, physical activity was significantly negatively correlated with insomnia (r = -0.178, p < 0.001) and depression (r = -0.231, p < 0.001), and significantly positively correlated with cognitive flexibility (r = 0.207, p < 0.001). Insomnia was significantly negatively correlated with cognitive flexibility (r = -0.387, p < 0.001) and significantly positively correlated with depression (r = 0.499, p < 0.001). Cognitive flexibility was significantly negatively correlated with depression (r = -0.504, p < 0.001).

Table 1.

Correlation analysis

Variables	1	2	3	4
1 Physical activity	-
2 Insomnia	−0.178***	-
3 Cognitive flexibility	0.207***	−0.387***	-
4 Depression	−0.231***	0.499***	−0.504***	-
M	22.87	15.46	17.84	13.74
SD	26.53	4.11	3.59	4.76

Note. ***: p<0.001

Mediation model testing

After controlling for gender and age, physical activity significantly and negatively predicted insomnia (β = -0.153, SE = 0.047, p < 0.01). However, in the indirect effect analysis, the predictive effect of physical activity on insomnia was no longer significant (β = -0.053, SE = 0.041, p > 0.05). Physical activity significantly and positively predicted cognitive flexibility (β = 0.151, SE = 0.046, p < 0.01) and significantly and negatively predicted depression (β = -0.110, SE = 0.041, p < 0.01). Cognitive flexibility significantly and negatively predicted both depression (β = -0.467, SE = 0.040, p < 0.001) and insomnia (β = -0.175, SE = 0.044, p < 0.001). Depression significantly and positively predicted insomnia (β = 0.404, SE = 0.045, p < 0.001). The mediation effects of physical activity on insomnia are detailed in Tables 2 and 3 and illustrated in Fig. 2.

Table 2.

Sequential mediation model test

Outcome variables	Predictor variables	β	SE	t	LLCI	ULCI	R 2	F
Insomnia	Physical activity	−0.153	0.047	−3.275**	−0.245	−0.061	0.045	7.719***
	Age	0.087	0.044	1.984*	0.001	0.173
	Gender	0.080	0.047	1.718	−0.012	0.172
Cognitive flexibility	Physical activity	0.151	0.046	3.271**	0.062	0.245	0.065	11.582***
	Age	0.007	0.043	0.171	−0.081	0.093
	Gender	−0.160	0.046	−3.450**	−0.254	−0.066
Depression	Physical activity	−0.110	0.041	−2.681**	−0.192	−0.029	0.276	47.214***
	Cognitive flexibility	−0.467	0.040	−11.823***	−0.552	−0.379
	Age	−0.031	0.038	−0.820	−0.110	0.047
	Gender	0.064	0.041	1.561	−0.021	0.148
Insomnia	Physical activity	−0.053	0.041	−1.297	−0.137	0.035	0.286	39.738***
	Cognitive flexibility	−0.175	0.044	−3.939***	−0.281	−0.079
	Depression	0.404	0.045	9.053***	0.287	0.515
	Age	0.102	0.038	2.694**	0.026	0.175
	Gender	−0.004	0.041	−0.090	−0.086	0.079

Note. *: p < 0.05; **: p < 0.01; ***: p < 0.001

Table 3.

Path analysis of sequential mediation model

Mediating path	Effect	SE	95% CI	Proportion of mediated effect
Total Effect	−0.153	0.047	−0.245,−0.061
Direct Effect	−0.053	0.041	−0.134, 0.028
Total Indirect Effect	−0.100	0.025	−0.152,−0.055	65.359%
PA→CF→Insomnia	−0.027	0.012	−0.055,−0.008	17.647%
PA→Depression→Insomnia	−0.045	0.019	−0.085,−0.011	29.412%
PA→CF→Depression→Insomnia	−0.029	0.011	−0.053,−0.011	18.954%

Note. PA = Physical activity; CF = Cognitive flexibility

Fig. 2.

Mediation model diagram. Note. **:p < 0.01; ***: p < 0.001

Discussion

This study identified the negative correlation between physical activity and insomnia, explored the mediating roles of cognitive flexibility and depression between physical activity and insomnia, and further validated the chain mediation effect of cognitive flexibility and depression. The findings underscore the positive benefits of physical activity, elucidate the mechanisms through which physical activity influences insomnia, and highlight the roles of other psychological variables in this relationship. This study strengthens the evidence for using physical activity as an intervention for insomnia among adolescents and provides pathways for future interventions and treatments.

Physical activity significantly negatively predicts insomnia, which is consistent with previous research findings [24, 25, 78–80]. This association has been repeatedly validated across diverse populations [81, 82]. A cross-cultural study demonstrated that the significant effect of physical activity on insomnia is not influenced by country or region [83], and the present study further strengthens this evidence. Although the efficacy of different intensities and types of physical activity in improving insomnia varies [27, 84], the evidence supporting the role of physical activity in alleviating insomnia severity and improving sleep quality continues to accumulate [85]. The mechanisms underlying the beneficial effects of physical activity on insomnia are increasingly well-documented. For instance, physical activity can improve sleep outcomes by reducing cortisol levels [83]. Additionally, the effects of physical activity on insomnia can be understood from multiple perspectives, including epigenetics, hyperarousal, circadian rhythms, and thermoregulation [84]. In the present study, we utilized the well-established and widely validated Physical Activity Rating Scale. However, the Cronbach’s alpha coefficient of this scale was 0.653, which did not meet the statistical standard of greater than 0.7. This issue has been addressed in previous research, which has shown that there is a wide range of physical activity measurement tools for adolescents, with significant differences in their reliability and validity assessments, indicating a need for further development and validation of authoritative tools [86]. Moreover, the Cronbach’s alpha coefficient can be influenced by factors such as the number of items and dimensions [87–89]. The current scale includes three dimensions and three effective items, which may contribute to the lower Cronbach’s alpha coefficient. Future studies are recommended to employ a combination of objective and subjective measurement methods, such as accelerometers, to enhance research quality.

The findings regarding the relationship between physical activity and cognitive flexibility in this study are in line with a substantial body of research [90, 91]. The association between cognitive flexibility and insomnia in our study is also consistent with some previous studies [42, 43], although other studies have demonstrated a bidirectional relationship between cognitive flexibility and insomnia [92]. A review study has pointed out that physical activity, insomnia, and cognitive flexibility are not only independently related but also share common associations [93], providing a foundation for the current research. Based on the bidirectional relationship between cognitive flexibility and insomnia, we found that the research on the relationships among physical activity, cognitive flexibility, and insomnia is not uniform. Some studies have identified the mediating role of sleep between physical activity and cognitive flexibility [93, 94], while others have demonstrated the mediating role of cognitive flexibility. For example, a study involving 416 adolescents showed significant negative correlations between physical activity and psychological inflexibility (r = -0.251, P < 0.01) and between physical activity and insomnia (r = -0.286, P < 0.01), as well as a significant positive correlation between psychological inflexibility and insomnia (r = 0.555, P < 0.01) [95]. These findings overlap with some of the results in our study and provide a foundation for the research on the role of physical activity in improving insomnia.

The correlations between physical activity and depression [52, 96] and between depression and insomnia [58, 62, 97] have been validated in previous studies. Based on the relationship between physical activity and insomnia, studies have indicated that the bidirectional relationship between sleep and physical activity over time is indirectly mediated through emotion regulation [98]. Additionally, research has demonstrated that the reciprocity between physical activity and sleep is achieved through multiple physiological and psychological pathways, including emotion [99]. These findings further strengthen the evidence supporting the current study. Depression plays a significant role in the potential mechanism by which physical activity compensates for the negative cognitive effects of sleep deprivation [100]. In a cross-sectional study involving 13,768 participants, depression was found to mediate the relationship between physical activity and sleep quality (β = -0.25, 95% bootstrap confidence interval: -0.28 to -0.21) [101]. Another study indicated that insomnia partially mediated the relationship between physical activity and depression (β = -0.095, 95% bootstrap CI: -0.123 to -0.067, p < 0.001) [92]. These differences can be further explained by the bidirectional relationship model between sleep and depression proposed in previous studies [102]. The findings of the current study are consistent with those of Su et al. [101], providing a more solid foundation for understanding the relationships among physical activity, depression, and insomnia despite differences in study populations and regions.

Based on the characteristic of cognitive flexibility to enhance stress resilience, the “dopamine hypothesis of positive affect” [103] reveals the mechanisms between cognition and emotion, providing a perspective for studying cognitive flexibility and negative emotions (e.g., depression). The correlation between cognitive flexibility and depression has been validated and supported by numerous studies. For example, one study showed a significant correlation between cognitive flexibility and depression levels (r = -0.60, p < 0.01) [68]. Other studies have demonstrated that cognitive flexibility can predict lower levels of depression [65–67] and that adolescents with depression exhibit reduced cognitive flexibility [62]. The cognitive-behavioral model of depression suggests that inflexible thinking processes lead to more negative emotions and behavioral problems, thereby increasing depressive symptoms [104], which helps us better understand the close relationship between cognitive flexibility and depression. The current study also confirmed this relationship.

The study findings have further elucidated the interrelationships among physical activity, insomnia, cognitive flexibility, and depression in adolescents. By examining the mediating roles and pathways of cognitive flexibility and depression, the study has uncovered the mechanisms through which physical activity can effectively intervene in insomnia. These findings provide a theoretical foundation for the design of multidimensional intervention programs. To effectively address insomnia and depression in adolescents, it is recommended to develop targeted physical activity programs that enhance cognitive flexibility among adolescents, with a focus on the type, duration, and modality of physical activity. Additionally, the development of exercise prescriptions aimed at improving adolescent insomnia is suggested. The integration of physical activity and cognitive training in educational curricula should be strengthened, and efforts should be made to foster a family environment that supports physical activity. A comprehensive, multilevel, and multi-stakeholder approach is essential to address the issue of adolescent insomnia effectively.

What’s more, there are still many aspects that need further exploration. For instance, negative experiences such as bullying victimization [105–107] and childhood abuse [108] may have a profound impact on adolescents’ mental health and sleep quality, which could potentially influence the relationship between physical activity and insomnia. These experiences may lead to negative emotions like depression [109–113], anxiety [114–116], and stress [95], which are also closely related to insomnia [95, 117]. Moreover, social support, particularly family support [115, 118], can play a significant role in buffering the negative effects of these experiences and emotions. Emotional regulation traits, such as alexithymia [119–121] and experiential avoidance [122, 123], may affect how adolescents cope with stress and negative emotions, thereby influencing their sleep quality. Additionally, the increasing prevalence of technology addiction [120, 124], including smartphone and internet addiction, may disrupt adolescents’ sleep patterns and exacerbate insomnia. Future research should consider these variables comprehensively to better understand the complex mechanisms underlying adolescent insomnia and develop more effective interventions.

Limitation

This study, based on the relationship between physical activity and insomnia among adolescents, explored the important roles of cognitive flexibility and depression in this relationship. However, as a cross-sectional study relying on self-reports, it could not avoid the subjectivity of self-reports and potential issues with data quality. The study focused on adolescents without extending to other population groups, limiting the generalizability of the findings. Future research should conduct cross-regional and cross-group studies to validate the mechanisms through which physical activity influences insomnia. Additionally, while cognitive flexibility and depression were chosen as mediating variables, other psychological variables were not included. Future studies should investigate the complex relationships among multiple psychological variables and physical activity and insomnia to provide more diverse intervention strategies for adolescent insomnia. The study employed a convenience sampling method, which inherently possesses certain geographical limitations. As a result, the findings may not objectively represent the characteristics of all secondary schools in Hunan Province. Future research is advised to increase the sample size and utilize random sampling or stratified sampling methods to enhance the generalizability of the results. Additionally, the study did not control for potential confounding variables, such as sociostructural factors (e.g., family income, parental education) and school environmental factors (e.g., academic pressure). Future research is recommended to incorporate a more comprehensive range of demographic information and additional psychological variables to better develop and refine theoretical models.

Conclusions

The present study elucidates the interrelationships among physical activity, insomnia, cognitive flexibility, and depression. Specifically, physical activity significantly and negatively predicts insomnia, with cognitive flexibility and depression acting as sequential mediators in this relationship. Future research should continue to emphasize the critical role of physical activity in the overall physical and mental health of adolescents. Longitudinal cohort studies are warranted to investigate the optimal dosage and duration of physical activity. Additionally, the development of hybrid intervention programs that integrate physical activity with cognitive-behavioral therapy (CBT) is recommended to explore their potential synergistic effects on sleep architecture.

Author contributions

Zhenxiu Yi 12456, Lifeng Wei 1256, Lei Xu 12356, Wenju Pang 356, Yang Liu 123456. 1 Conceptualization; 2 Methodology; 3 Data curation; 4 Writing - Original Draft; 5 Writing - Review & Editing; 6 Funding acquisition.

Funding

Key Research Base of Humanities and Social Sciences in Guangxi Universities “Research Center for Cultural Construction and Social Governance in Ethnic Regions”(2023YJJDZD03).

Data availability

The datasets generated and/or analysed during the current study are not publicly available due [our experimental team’s policy] but are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

The study was approved by the Ethics Committee of Chengdu Sport University before the initiation of the project (Grant number: [2024]98). Informed consent was obtained from the participants and their guardians before the start of the program. We confirm that all the experiment is in accordance with the relevant guidelines and regulations such as the declaration of Helsinki.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.