Physical Activity Habit Automaticity, Psychological Distress, and Quality of Life Among Chinese University Students: A Three-Wave Longitudinal Moderated Mediation Study

Background: Physical activity is widely linked to better mental health and quality of life in university students, but less is known about whether the automatic, habit-like quality of physical activity is prospectively associated with quality of life through psychological distress and whether this indirect association depends on exercise identity. The objective of this study was to test a three-wave longitudinal moderated mediation model linking T1 physical activity habit automaticity, T2 psychological distress, T3 quality of life, and T1 exercise identity. Methods: A three-wave longitudinal survey was conducted among Chinese university students in 2026. After data cleaning and anonymous matching across waves, the final analytic sample included 1024 students, of whom 58.98% were female. T1 physical activity habit automaticity was assessed using the Self-Report Behavioral Automaticity Index, T1 exercise identity using the Exercise Identity Scale, T2 psychological distress using the Patient Health Questionnaire-4, and T3 quality of life using the EUROHIS-QOL 8-item index. PROCESS Model 4 and Model 7 were estimated with 5000 bootstrap samples, controlling for sex, age, grade, physical activity frequency, sleep quality, baseline psychological distress, and baseline quality of life. Results: In the baseline-adjusted mediation model, T1 physical activity habit automaticity was negatively associated with T2 psychological distress (B = −0.503, p < 0.001), and T2 psychological distress was negatively associated with T3 quality of life (B = −0.086, p < 0.001). The indirect effect was significant (effect = 0.043, 95% CI [0.028, 0.059]), with a mediated proportion of 30.9%, while the direct effect remained significant. In the moderated mediation model, the habit automaticity × exercise identity interaction significantly predicted T2 psychological distress (B = −0.317, p < 0.001, ΔR2 = 0.008). Conditional indirect effects were significant at mean and high levels of exercise identity, and the index of moderated mediation was significant (index = 0.027, 95% CI [0.012, 0.043]). Conclusions: Physical activity habit automaticity was prospectively associated with higher quality of life partly through lower psychological distress, and this indirect association was more pronounced among students with stronger exercise identity. The findings highlight habit formation and exercise identity as potentially relevant targets for campus health promotion, although causal conclusions remain limited by the observational design.