BACKGROUND: During isolation, sharing physical activity experiences on social network sites (SNS) can enhance individual social connectedness. The objective of the present study was to examine the associations between sharing physical activity experiences on SNS, positive self-presentation, positive feedback, and social connectedness during isolation. METHODS: Based on the Physical Activity Experience Sharing Scale, Social Connectedness Scale, Positive Self-Presentation Scale, and Online Positive Feedback Scale, we collected 460 questionnaires online from across 31 provinces, municipalities and autonomous regions in China. We used multiple linear regression models to investigate the relationship between variables, and used bootstrapping to test for mediation.. RESULTS: During isolation, sharing physical activity experiences was positively associated with social connectedness (b = 0.308, p < 0.001), as well as with positive self-presentation(b = 0.956, p < 0.001)and positive feedback(b = 0.421, p < 0.001). In addition,we found that positive self-presentation showed a significant positive impact on positive feedback (b = 0.563, p < 0.001), and that positive self-presentation(b = 0.331, p < 0.001) and positive feedback(b = 0.311, p < 0.001) were positively associated with social connectedness. Finally, we found an effect on sharing physical activity experiences indirectly through positive self-presentation (b = 0.316, 95% CI: [0.180, 0.463]),and positive feedback (b = 0.131, 95% CI: [0.063, 0.207]) and that the mediation chain between the two also had a significant impact on social connectedness (b = 0.167, 95% CI: [0.088, 0.251]). CONCLUSIONS: During the COVID-19 pandemic, sharing physical activity experiences on SNS can create a positive, healthy, and energetic personal image, gain recognition from others, and establish new interpersonal relationships.