Feasibility of an Augmented Two-Day Step Test and Causal Modeling for Post-Exertional Symptom Exacerbation in Post Covid-19 Syndrome

This study aims to evaluate exercise capacity and identify causes of Post-Exertional Symptom Exacerbation (PESE) in individuals with Long COVID. The investigators will compare the effectiveness of the Two-Day 6-Minute Incremental Step Test (6MIST) and the Cardiopulmonary Exercise Test (CPET) in detecting PESE. Additionally, the investigators will assess metabolism, mitochondrial function, autonomic symptoms, psychological factors, and physical activity. Participants will complete both the Two-Day 6MIST and the Two-Day CPET, with a one-month gap between them. Each test is performed on two consecutive days to assess the delayed symptom response. The subjective symptoms of PESE will also be measured through questionnaires. To explore potential causes of PESE, the investigators will measure metabolism using indirect calorimetry, bioelectrical impedance analysis and food diaries, mitochondrial dysfunction with NIRS technology, autonomic symptoms using the COMPASS-31 questionnaire, psychological factors with questionnaires and physical activity levels using an activity tracker. This study will determine if the Two-Day Step Test (6MIST) is a feasible alternative to the two-day CPET for measuring PESE and will help uncover underlying mechanisms contributing to symptom exacerbation.