Objective: To investigate the relationship between physical activity and negative emotions among college students in the post-epidemic era and determine if emotional regulation plays a mediating role between physical activity and negative emotions. Methods: 479 college students (293 males, 186 females, M = 19.94, SD = 1.25) who were under closed campus management during the epidemic period were surveyed using the physical activity rating scale (PARS-3), the self-assessment scale for anxiety (SAS), the self-esteem scale for depression (SDS), and the emotion regulation self-efficacy scale (RES). Results: (1) Physical activity, negative emotions, and emotion regulation self-efficacy among college students were significantly different by gender (p < 0.01). (2) Physical exercise was negatively correlated with anxiety and depression (r = −0.236, p < 0.01; r = −0.198, p < 0.01) and positively correlated with emotion regulation self-efficacy (r = 0.256, p < 0.01) in college students. (3) Emotion regulation self-efficacy was negatively correlated with anxiety and depression (r = −0.440, p < 0.01; r = −0.163, p < 0.01). (4) Emotion regulation self-efficacy also partially mediated the relationship between physical activity and negative emotions. Conclusion: (1) Physical activity in the post-epidemic era negatively predicted anxiety and depression in school-isolated college students. (2) Emotion regulation self-efficacy in the post-epidemic era partially mediates the relationship between physical activity and anxiety and depression.

Considering the role of school adjustment in the development of adolescent populations, it is particularly essential to find ways to improve the school adjustment of middle school students and to develop further the socialization of adolescents. Based on the 2014–2015 data of the China Education Panel Survey, the effects of physical exercise on adolescents’ school adjustment and possible mechanisms were systematically explored. Based on the ordinary least squares method, instrumental variable method, and propensity score matching method, the results of the study showed that physical exercise significantly improved adolescents’ school adjustment. The results of the mediation effects test indicated that physical exercise not only enhances adolescents’ school adjustment by alleviating negative emotions, but also enhances adolescents’ school adjustment by improving prosocial behavior. This study reveals the mechanism of physical exercise and adolescents’ school adjustment, and provides reasonable and effective suggestions for better promoting adolescents’ school adjustment and formulating related policies.