Author(s): WANG, C., ZHANG, Y., Institution: CHINA INSTITUTE OF SPORT SCIENCE, Country: CHINA, Abstract-ID: 1466

INTRODUCTION:
Physical activity is widely promoted for mental health benefits; however, the underlying mechanisms remain unclear. In particular, it is unknown whether physical fitness represents a key pathway linking physical activity to specific psychological symptoms. This study examined the differential associations of physical activity, physical fitness, and sleep duration with stress, anxiety, and depression in adolescents, and tested the mediating role of physical fitness.
METHODS:
A total of 4,376 adolescents were drawn from the Macau National Physical Fitness Surveillance system in this cross-sectional study. Physical activity level and sleep duration were assessed using standardized questionnaires. Physical fitness was derived from objective fitness testing. Stress, anxiety, and depressive symptoms were assessed using the Depression Anxiety Stress Scales-21 (DASS-21).The DASS-21 has demonstrated good psychometric properties in adolescent populations.Pearson correlations, hierarchical regression analyses controlling for age and sex, and bootstrapped mediation analyses (5,000 resamples) were performed.
RESULTS:
Physical fitness was negatively associated with anxiety (r = −.089, p < .001) and depression (r = −.096, p < .001), but not with stress (r = −.039, p = .127). Physical activity showed weak correlations with anxiety (r = −.051, p = .017) and depression (r = −.077, p < .001), and no association with stress. Sleep duration was consistently related to lower stress (r = −.140), anxiety (r = −.132), and depression (r = −.163) (all p < .001).
In regression models, sleep duration was a robust predictor across all outcomes (β range = −.153 to −.170, p < .001). Physical fitness significantly predicted anxiety (β = −.111, p < .001) and depression (β = −.087, p = .002), but not stress (p = .090). Physical activity was not a significant direct predictor after adjustment.
Mediation analyses revealed significant indirect effects of physical activity on anxiety (indirect effect = −.0083, 95% CI [−.0123, −.0042]) and depression (indirect effect = −.0072, 95% CI [−.0117, −.0031]) via physical fitness. No mediation effect was observed for stress.
CONCLUSION:
Physical fitness significantly predicted anxiety and depressive symptoms, whereas physical activity showed no direct association after adjustment. Mediation analyses further demonstrated that physical fitness fully mediated the relationship between physical activity and both anxiety and depression. In contrast, physical fitness was not significantly associated with stress symptoms, whereas sleep duration remained a significant predictor. Together, these findings suggest that measurable fitness capacity, rather than activity exposure alone, may represent a key mechanism linking sport participation to psychological health in adolescents.