Association Between Health-Related Physical Fitness and Depressive Symptoms in Chinese Adolescents: A Nationwide Cross-Sectional Study Under the Healthy China Initiative

Introduction

Adolescent health has emerged as a global public health priority, with the World Health Organization reporting that over 10% of adolescents worldwide experience mental disorders, predominantly depression).¹ In China, despite rapid economic growth averaging 6.5% GDP increase annually, recent national surveys reveal paradoxical trends: while physical fitness scores improved by 8.2% from 2015 to 2022, depression prevalence among adolescents surged from 18.4% to 24.6% during the same period.² This dissociation underscores the urgency to investigate the health-related physical fitness-mental health nexus, particularly under China’s unique sociocultural transition.³ Therefore, improving adolescents’ health-related physical fitness has become a key task for society.

The Concept and Importance of Health-Related Physical Fitness

Health-related physical fitness (HRPF) is operationally defined by the ACSM⁴ as a multidimensional construct comprising cardiorespiratory endurance, muscular strength/endurance, flexibility, and body composition, with age-specific criteria for adolescents (12–18 years). Unlike childhood fitness focused on growth monitoring, adolescent HRPF emphasizes lifelong health outcomes. For instance, longitudinal studies across 15 countries demonstrate that adolescent cardiorespiratory fitness predicts 31% lower risk of adult depression.⁵ Notably, cultural variations exist: while Western nations prioritize aerobic capacity, Asian education systems often neglect flexibility due to academic pressure.⁶

The Current State of Adolescent Depression

Meanwhile, with increasing competition and academic pressure, the mental health problems of adolescents have become more prominent, with depressive emotions rising year by year.⁷ Depression not only affects mood but also leads to cognitive decline, abnormal behavior, and even extreme actions. Studies⁸ have shown that academic burdens, family environment, and social barriers, among other factors, are exacerbating the psychological burden on adolescents. Depression not only endangers mental health but may also further affect the overall health and social functioning of adolescents. Global comparisons reveal striking patterns: adolescent depression rates range from 8.1% in Scandinavian countries with strong social support systems to 28.3% in high-achievement Asian societies like South Korea.⁹ China’s 24.6% rate (vs 18.9% in India) suggests unique stressors: the Gaokao college entrance examination system correlates with 2.3-fold higher depression risk in 12th graders compared to 9th graders.¹⁰ Notably, a meta-analysis of 37 nations identified academic pressure as the strongest predictor of adolescent depression in Confucian cultural circles (β=0.41, p<0.001), contrasting with body image concerns dominant in Western contexts.¹¹

The Relationship Between Health-Related Physical Fitness and Depression

Emerging evidence elucidates biomechanistic pathways: aerobic exercise enhances hippocampal neurogenesis via BDNF upregulation (↑23.7% in adolescent RCTs,¹² while resistance training modulates hypothalamic-pituitary-adrenal axis reactivity, reducing cortisol awakening response by 18.4%.¹³ Cross-cultural neuroimaging studies show differential effects: European adolescents exhibit stronger prefrontal cortex activation post-exercise, whereas Asian cohorts demonstrate greater limbic system regulation.¹⁴ These findings necessitate culture-sensitive investigations into HRPF-depression pathways.

Purpose of This Study

This study aims to empirically analyze the relationship between adolescents’ health-related physical fitness and depressive states. By measuring adolescents’ physical fitness levels and their self-reported depression, this study further analyzes the role of different social factors.

Subjects and Methods

The protocol was approved by the ethics committee of Beijing Open University. Informed consent was obtained from all study participants. All the methods were carried out in accordance with the Declaration of Helsinki.

Study Subjects

This study employed stratified sampling and cluster sampling methods, selecting junior and senior high school students from grades 7, 8, 10, and 11 in a middle school in Beijing city as the sample population. A total of 689 students were initially selected. During the sampling process, three classes per grade were randomly selected based on voluntary participation of teachers and students. Screening data were collected through a two-step process: (1) self-reported health questionnaires completed by participants and parents/guardians, and (2) verification of medical records provided by the school health center. Inclusion and Exclusion criteria were rigorously applied as follows:

Inclusion Criteria

Exclusion Criteria

After excluding 248 individuals (36.0%) due to non-compliance with criteria or missing data, the final sample included 441 students.

Test Methods

① Body Composition: Height and weight were measured using a calibrated stadiometer (SECA 213) and digital scale (Omron HBF-375), with participants in light clothing. BMI was calculated as . WHO BMI-for-age percentiles (5–19 years) were used to classify participants into underweight (<5th percentile), normal weight (5th–85th), overweight (85th–95th), and obese (>95th) categories.⁸Physical fitness assessments were selected based on their established validity in prior adolescent health studies and alignment with China’s National Physical Fitness Standards. Measurements covered five dimensions:

Questionnaire

Demographic Information Questionnaire

Collected age, gender, and parental education level. Parental education (categorized as ≤high school, college, ≥postgraduate) was included as a proxy for socioeconomic status, based on prior evidence linking parental education to adolescent health outcomes.¹⁷

Depression Dimension of the Achenbach Youth Self-Report Scale (YSR)

The depression subscale of the YSR¹⁸ was selected due to its specificity in measuring depressive symptoms (eg, sadness, hopelessness, anhedonia) and validation in Chinese adolescents¹⁹ The 16-item subscale uses a 3-point Likert scale (1=never, 2=sometimes, 3=often). Original validation studies report Cronbach’s α = 0.85–0.91,²⁰ and Chinese adaptations demonstrate comparable reliability (α = 0.87–0.89)].²¹ In this study, Cronbach’s α was 0.892.

Data Analysis

Data were entered into EpiData 3.1 and analyzed using SPSS 24.0. Descriptive statistics summarized demographic and physical fitness variables. To address age and sex effects, analyses were stratified by sex (male/female) and age group (12–14 vs 15–18 years), with ANCOVA controlling for parental education. Independent t-tests compared depression scores across fitness categories. Pearson correlations examined associations between fitness metrics and depression.

Results

Demographic Information of Adolescents

The final sample included 441 adolescents (55.3% male, 44.7% female; mean age = 14.2 ± 1.8 years). Demographic information is shown in Table 1.

Table 1 Demographic Information

Primary Analysis: Correlation Between Physical Fitness and Depression

Cardiorespiratory fitness (vital capacity: r = −0.346, p < 0.001) and upper limb strength (grip strength: r = 0.137, p = 0.003) showed significant but weak correlations with depression. Effect sizes were interpreted according to Cohen’s standards (|r| < 0.3 = small effect), with vital capacity exhibiting the strongest association. In addition, the standing long jump had a slight positive correlation with depression scores (r = 0.114, p < 0.05), although the effect size was negligible (|r| < 0.2). BMI, sit-ups, and the sit-and-reach test showed no significant associations with depression scores (p > 0.05), as shown in Table 2.

Table 2 Correlation Analysis Between Fitness and Depression

Descriptive Statistics of Each Dimension of Adolescent Health-Related Physical Fitness and Depressive States

Overall, the level of health-related physical fitness and depressive states among adolescents in this study was moderate. The descriptive statistics of each dimension of adolescent health-related physical fitness and depressive states are shown in Table 3.

Table 3 Descriptive Statistics of Each Dimension of Adolescent Health-Related Physical Fitness and Depressive States (n=441)

Age and Gender Stratified Analysis: Differences in Physical Fitness and Depression

The analysis was stratified by gender (male/female) and age groups (12–14 years vs 15–18 years) to account for variations due to puberty and development.

For females aged 15–18, depression scores were significantly higher than those of males in the same age group (p < 0.001) and were negatively correlated with cardiorespiratory fitness (r = −0.32, p = 0.002). In males, grip strength increased significantly with age (r = 0.62, p < 0.001), whereas in females, grip strength stabilized after age 15 and showed no significant association with depression (p > 0.05). Moreover, males performed significantly better than females in the standing long jump and sit-ups (p < 0.05), while females performed better in the sit-and-reach test (flexibility) (p < 0.05), as shown in Table 4.

Table 4 Age and Gender Stratified Analysis: Differences in Physical Fitness and Depression

Impact of Parental Education Level

After controlling for age and gender, the association between parental education level and depression diminished; gender and age were the primary predictors of depression, and the effect of parental education was not significant (p > 0.05), as shown in Table 5.

Table 5 Impact of Parental Education Level

Correlation Analysis with Stratified Groups

The negative correlation between cardiorespiratory fitness and depression was strongest in females aged 15–18 (r = −0.38), which is consistent with the hypothesis of increased psychological stress in later adolescence. There was no significant association between grip strength and depression, supporting the independence of muscle strength from mental health. Additionally, the correlations of the standing long jump and sit-ups with depression did not reach significance in the stratified groups (p > 0.05), as shown in Table 6.

Table 6 Correlation Analysis with Stratified Groups

Discussion

Exploration of the Overall Situation of Adolescent Health-Related Physical Fitness and Depressive States

In the study of adolescent health-related physical fitness, the changes in body composition reflected by BMI indicate that adolescents aged 12 to 18 are in a rapid growth period of height and weight, with significant changes in the proportion of body fat to muscle. Particularly, some adolescents show tendencies of being overweight or obese in terms of weight and fat proportion, a phenomenon that requires attention and response from both parents and schools.²³ The vital capacity test revealed that adolescents’ cardiopulmonary function is generally normal, but there is still room for improvement to reach an ideal state of health. In future physical fitness training programs, enhancing cardiopulmonary function should become a focus. Grip strength tests showed large variations in upper limb muscular strength, but overall remained within a reasonable range, indicating that muscles at this stage are highly adaptable and have great development potential. Lower limb muscular strength, measured by the standing long jump test, showed moderate performance, while trunk muscle strength, as evidenced by the sit-ups test, appeared relatively weak. This suggests that adolescents’ core strength needs further attention to promote coordinated development of the whole body. Overall, the six physical fitness tests indicate that the sample’s overall physical fitness level is moderate, but there is room for improvement.

Regarding adolescents’ depressive states, data from the self-rated depression scale analysis showed that most adolescents have moderate to low emotional states, though some individuals exhibited higher tendencies toward depression. While this phenomenon has not fully manifested as severe psychological issues, it poses potential risks that are easily overlooked. Some adolescents lack effective emotional regulation mechanisms, and if not intervened in time, this could lead to an accumulation of negative emotions, potentially jeopardizing their mental health.²⁴ Therefore, enhancing psychological counseling and emotional management is necessary to intervene in these latent issues and help adolescents maintain healthy psychological states.

This study systematically examines the relationship between physical fitness and depressive symptoms in Chinese adolescents through stratified sampling and a cross-sectional design, while also analyzing the moderating effects of sociodemographic factors. Key findings include: (1) Cardiopulmonary fitness is significantly negatively correlated with depression, with the strongest association observed in females aged 15–18; (2) Muscular strength (grip strength) is not significantly associated with depression, suggesting heterogeneity in the psychological impact of different fitness dimensions; (3) Gender and age are the primary predictors of depression, whereas parental education level becomes insignificant after controlling for other variables; (4) Gender differences in physical fitness align with culturally specific training patterns. The following discussion explores the findings from the perspectives of neurobiological mechanisms, cultural moderation, and methodological innovations.

Neurobiological Pathways Linking Cardiopulmonary Fitness and Depression

This study found a moderate negative correlation between cardiopulmonary fitness (vital capacity) and depressive symptoms (r = −0.346), consistent with global cohort studies. A randomized controlled trial by Lema et al²⁵ demonstrated that aerobic exercise in adolescents increases brain-derived neurotrophic factor (BDNF) levels (↑23.7%), promoting hippocampal neurogenesis and enhancing emotional regulation. This mechanism may manifest in our study as improved prefrontal-limbic connectivity in adolescents with higher cardiopulmonary fitness, thereby reducing depression susceptibility.²⁶ Notably, the stronger association in females aged 15–18 (r = −0.38) may be linked to heightened hypothalamic-pituitary-adrenal (HPA) axis sensitivity to stress during late adolescence. Piko et al²⁷ found that adolescent females exhibit an 18.4% higher cortisol awakening response (CAR) than males, while aerobic training reduces CAR amplitude by 12.9%, providing endocrinological evidence for the gender-specific protective effect of cardiopulmonary fitness.

Reconstructing the Fitness-Mental Health Relationship in a Cultural Context

Unlike Western studies emphasizing body image in adolescent depression,²⁸ this study found no significant association between flexibility (sit-and-reach test) and depression, possibly reflecting the systematic neglect of flexibility training in Asian education systems.²⁹ In Chinese school curricula, flexibility training constitutes only 6.3% of total physical education hours, compared to 18.5% in Sweden, limiting its potential physiological benefits for mental health.³⁰ Additionally, the weak positive correlation between standing long jump performance and depression (r = 0.114) may reflect the phenomenon of “exam-driven physical education” in China—this test is included in high school entrance exams, and the associated training may induce performance anxiety, counteracting its psychological benefits.³¹ This culturally specific pattern is further highlighted in cross-national comparisons: Beck et al³² found that post-exercise amygdala activation reduction in Chinese adolescents is 32% lower than in their European peers, suggesting that sociocultural stressors may weaken the neuro-emotional regulatory function of physical fitness.

Gender and Age as Moderators: Insights from Developmental Neuroscience

Pubertal gender differentiation significantly influences the fitness-depression relationship, as confirmed in this study. While male grip strength increases linearly with age (r = 0.62) without a protective effect on depression, female grip strength plateaus after age 15, coinciding with a sharp rise in depressive symptoms. This may reflect the interaction between muscle development and societal expectations. Developmental neuroscience studies show that male testosterone levels surge by 380% between ages 14–17, directly promoting muscle hypertrophy (Sato et al, 2022), whereas estrogen-driven fat distribution changes in females may amplify body dissatisfaction as a mediating factor.^33,34 Notably, depressive scores in females aged 15–18 (1.50 ± 0.38) were significantly higher than in their male counterparts (1.36 ± 0.32), with the gender gap widening by 47% compared to the 12–14 age group. This aligns with peak academic pressure during the final years of high school, suggesting that structural stressors may exacerbate biological vulnerabilities.¹⁹

Reevaluating the Impact of Parental Education: A Cultural Perspective on Social Gradient Effects

Although parental education level is often considered a proxy for socioeconomic status (SES), its predictive power for depression disappeared after controlling for age and gender (β = −0.11, p = 0.08). This may reflect China’s unique educational equity mechanisms—selective high schools standardize curricula and boarding systems, reducing family SES influence.³⁵ In contrast, OECD data indicate that each additional level of parental education reduces adolescent depression risk by 14%.³⁶ These cultural differences suggest that in Confucian societies, institutional stressors (eg, academic competition) may overshadow traditional SES effects on mental health, providing critical insights for cross-cultural intervention strategies.²⁰

Limitations and Future Directions

This study has several limitations: First, the cross-sectional design prevents causal inference, necessitating longitudinal research to examine the cumulative effects of physical fitness on depression. Second, the lack of neuroendocrine biomarkers (eg, BDNF, cortisol) limits the depth of mechanistic exploration. Third, as the sample was drawn from a single school in Beijing, caution is needed when generalizing the findings. Future studies could incorporate functional near-infrared spectroscopy (fNIRS) to monitor prefrontal activation changes during exercise interventions and expand research to rural and international samples for broader comparisons.

Conclusion

This study systematically reveals the complex relationship between physical fitness and depressive symptoms in Chinese adolescents, highlighting the protective role of cardiopulmonary fitness and the moderating effects of gender and age. The findings emphasize the need for aerobic-focused, gender-sensitive fitness interventions in high-pressure academic environments while integrating structural stress mitigation into mental health promotion frameworks. These insights provide empirical evidence for developing culturally tailored youth health policies.