Associations between self-control and physical activity among college students: a cross-sectional serial indirect-effect analysis of smartphone addiction and autonomous motivation for exercise

Background Physical inactivity and problematic smartphone use are common concerns among college students, and self-control has been identified as an important self-regulatory factor related to health behavior. However, it remains unclear whether smartphone addiction and autonomous motivation for exercise independently and sequentially account statistically for the association between self-control and physical activity. Methods We conducted a cross-sectional survey of 1,469 Chinese college students (all aged 18 years or older; 573 male, 39.0%; 896 female, 61.0%) from five higher education institutions in Kunming, Yunnan Province, China. Self-control was measured using the 13-item Brief Self-Control Scale; smartphone addiction was assessed using the 10-item Smartphone Addiction Scale–Short Version; autonomous motivation for exercise was assessed using the identified regulation and intrinsic regulation subscales of the Behavioural Regulation in Exercise Questionnaire-2; and physical activity was assessed using the Physical Activity Rating Scale-3. Covariate-adjusted specific and sequential statistical indirect effects were estimated using PROCESS Model 6 with 5,000 bootstrap resamples and adjustment for sex, grade level, place of origin, and only-child status. Results Self-control was positively associated with physical activity (total effect B = 3.6098, 95% CI [2.4139, 4.8057]). A direct association remained statistically significant after accounting for both intervening variables ( B = 1.9764, 95% CI [0.8261, 3.1267]), and the total indirect effect was B = 1.6334 (95% CI [1.1878, 2.0975]). Statistically significant indirect effects were observed via smartphone addiction ( B = 0.3495, 95% CI [0.1212, 0.6109]), via autonomous motivation for exercise ( B = 1.0385, 95% CI [0.6638, 1.4300]), and sequentially via smartphone addiction and autonomous motivation for exercise ( B = 0.2454, 95% CI [0.1552, 0.3562]). Conclusion Higher self-control was associated with greater physical activity, with statistical indirect effects via smartphone addiction and autonomous motivation for exercise. These findings highlight the potential relevance of addressing problematic smartphone use and supporting autonomous exercise motivation when promoting physical activity among college students. Because the data were cross-sectional, self-reported, and adjusted only for selected demographic covariates, these indirect effects should not be interpreted as evidence of temporal ordering or causal mediation.