Background: In order to gain a deeper understanding of the relationship between physical activity and adolescent mental health in the post COVID-19 pandemic era, self-esteem and social anxiety were used as mediating variables to explore the potential mechanisms by which physical activity affects adolescent mental health. Methods: The study used the HELP-II Health Promoting Lifestyle Scale, the SPIN Social Phobia Scale, the Self-Esteem Scale, and the 10-item Kessler Psychological Distress Scale to administer questionnaires to 400 Chinese secondary school students, and SPSS 26.0 and PROCESS 3.3 were used to process the data. Results: The findings showed that (1) physical activity was significantly and positively associated with mental health; (2) self-esteem and social anxiety played a fully mediating role between physical activity and adolescent mental health respectively; (3) self-esteem and social anxiety played a chain mediating role between physical activity and adolescent mental health. Conclusion: This study reveals the relationship and influencing mechanism between physical activity and adolescent mental health in the post COVID-19 pandemic era. Appropriate interventions for physical activity, self-esteem, and social anxiety may be beneficial to adolescent mental health. The protective role of self-esteem in adolescent mental health should be the focus of future studies, and further investigations into the association between the COVID-19 and adolescent mental health are warranted.

Students majoring in physical education are the main source of physical education teachers in Chinese schools, and they are the main body in achieving the function of physical education in schools. The improvement of their altruistic behavior helps enhance the educational literacy of outstanding physical education teachers. This study conducted a questionnaire survey on 310 students majoring in physical education from 5 universities in 5 selected regions using the General Interpersonal Communication Objective Scale, Interpersonal Reactivity Index-C, the “responsibility” subscale of the Big Five Inventory Questionnaire, and the Altruistic Behavior of College Students questionnaire. We performed correlation analysis, mediation effect analysis, and moderation effect analysis on the data using SPSS 24.0 and MPLUS 7.4. Empathy partially mediates 30% of the total effect between interpersonal relationships and altruistic behavior; social responsibility has a moderating effect on empathy and altruistic behavior, with higher levels of responsibility having a greater moderating effect. Interpersonal relationships, empathy, and a sense of responsibility affect the current, recent, and long-term states of altruistic behavior, respectively. To improve students’ altruistic behavior throughout the entire process, schools should develop training systems specifically for interpersonal relationships, empathy, and social responsibility.