Physical activity and sleep quality: exploring the mediating role of depression and the moderating role of physical fitness among adolescents

The impact of academic pressure on high school students manifests in reduced physical activity, deteriorated health, elevated levels of depression and anxiety, ultimately compromising sleep quality (SQ). While the association between physical activity and SQ is recognized, the underlying mechanisms remain underexplored. Thus, observational research was used in this study to analyze a hypothesized pathway between physical activity and SQ, analyze whether depression serves as a mediating variable in the association between physical activity and SQ, and whether physical fitness acts as a moderating factor between depression and SQ among adolescents. This study aims not only to elucidate the mechanisms underlying the relationship between physical activity, depression, and SQ but also to provide actionable insights for intervention design. For instance, schools could adopt these findings to structure physical education curricula that address common adolescent mental health challenges. Additionally, the results can inform policy recommendations for adolescent health promotion, emphasizing the dual benefits of physical fitness and mental health management in improving SQ. 615 senior high school students were investigated (39.2% boys; mean age: 17.26 ± 1.25 years old). Participants completed questionnaires on physical activity levels, SQ, and depression, while physical fitness was assessed using the China Students’ Physical Health Standard Test Battery. Pearson correlation was used to explore the association between physical activity, depression, physical fitness and SQ. The Bootstrap method with the PROCESS macro was used to examine the mediation effect of depression and the moderation effect of physical fitness. The results showed that lower PSQI scores (indicating better SQ) were associated with higher levels of physical activity and better physical fitness, and with lower levels of depressive symptoms (p < 0.01). Notably, depression mediates the relationship between physical activity and SQ (β (95% CI): -0.34 (-0.49, -0.20)), while physical fitness moderates the impact of depression on SQ (p = 0.015, β (95% CI): 0.003 (0.001, 0.006)). Our results indicate that higher levels of physical activity and physical fitness are associated with lower depressive symptoms, which are in turn associated with better SQ among adolescents.