**6. Conclusions**

Our results showed that, first, in the criterion layer, the weight of PU was 0.2808, which was much larger than that of the other indicators, indicating that PU most strongly influenced the study group's use of fitness apps under the influence of COVID-19. Among the criteria that we used for measuring PU, the study group was more concerned about content adaptability. Therefore, developers of health apps need to pay attention to the special traits of users, provide more customized and scientific strategies and content, and select reasonable and scientific fitness programs tailored to users according to their age, occupation, height, weight, personal preferences, etc. Second, the weights of personal motivation and PEOU were 0.2630 and 0.2565, respectively, indicating their stronger impact on the willingness of the study groups to use fitness apps. We recommend that fitness APP developers pay attention to the different characteristics of users and provide more personalized service methods and content, improve the fun of exercise, and reduce the fatigue experienced when users exercise. Third, the perceived cost had the lowest weight of 0.1997, indicating a weaker influence on the group's use of fitness apps. The data of the indicators measuring the perceived cost showed that the study group was much more worried about privacy than the financial cost, indicating that the group had a strong sense of privacy. Security and privacy policies imply a commitment to users' personal information. Due to the small operating interface of cell phones and portable devices, companies should proactively and prominently display protection policies so that users can feel the company's commitment to security and privacy.

Currently, the COVID-19 pandemic is still ongoing. Increasing people's physical activity during the pandemic to ensure physical and mental health and to improve the well-being of the population remains a difficult task. The data from this study can help subsequent fitness app developers understand user needs and provide an empirical basis for subsequent fitness app development or iterations.

**Author Contributions:** Conceptualization, Y.G. and D.C.; methodology, Y.G. and H.Z.; software, X.M.; validation, Y.G. and D.C.; formal analysis, Y.G.; investigation, Y.G. and X.M.; resources, Y.G.; data curation, X.M.; writing—original draft preparation, Y.G. and H.Z.; writing—review and editing, Y.G.; visualization, X.M.; supervision, Y.G.; project administration, Y.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was conducted by the Anhui University 2020 Talent Introduction Scientific Research Start-up Fund Project (Project No. S020318019/001).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The experimental data used to support the findings of this study are included in the article.

**Conflicts of Interest:** The authors declare no conflict of interest.
