A Mobile Research App for Post-COVID Fatigue Monitoring.

Post-COVID fatigue is a common and burdensome symptom that fluctuates throughout the day, making it difficult to assess within clinical visits. To capture post-COVID symptom fatigue in daily settings, we developed a mobile research app based on a previous survey-based tool, designed as a progressive web application (PWA) using React. The app combines offline functionality, flexible testing times, visual instructions and local storage of participant data. The development was guided by a requirements analysis conducted through interviews with patients, identifying core needs for usability, flexibility and personalized tracking. Compared to a survey-based tool, key improvements include reduced cognitive load, a modern, minimalist design and optimization for mobile devices. Technical tests across Android and iOS devices confirmed stable and compatible performance. Future work includes a systematic usability and feasibility evaluation with both healthy participants and post-COVID patients. The application provides a flexible, user-friendly platform for symptom tracking for post-COVID studies and has potential for further development into self-management for patients.