Using Active Standing Orthostatic Stress Test to Assess Physiological Responses in Individuals with Long-COVID: A Systematic Review

Background/Objective: Individuals experiencing long-COVID frequently report or-thostatic intolerance symptoms, which may be linked to autonomic and cardiovascular dysfunction. The active standing test provides a simple, clinically relevant means to assess these impairments. This systematic review aims to determine the use of the ac-tive standing orthostatic stress test in evaluating cardiovascular, autonomic, and res-piratory responses in people experiencing LC. Methods: A systematic search, accord-ing to PRISMA guidelines, was conducted in PubMed, MEDLINE, EMBASE, CINAHL, and Scopus for articles published between 2020 and 2025. This study was registered in PROSPERO CRD-42024615872. Studies were included if they used the active standing test, enrolled adults (≥18 years), included both Long-COVID and healthy control groups, used continuous beat-to-beat measurements, and reported physiological out-comes. Risk of bias was assessed using the nine-point Newcastle-Ottawa-Scale. Re-sults: Three studies (216 participants with Long-COVID and 186 controls) met the in-clusion criteria. Across studies, Long-COVID individuals consistently exhibited ele-vated heart rate in both supine and standing positions. However, blood pressure find-ings were more variable: only one study reported 13% of participants met orthostatic hypotension criteria, while another found significant increases in diastolic blood pres-sure during standing. Long-COVID groups also showed reduced heart rate variability compared to controls. Conclusions: Individuals experiencing Long-COVID show ele-vated heart rate and impaired autonomic function during active standing, with sub-group-specific blood pressure changes. These alterations may contribute to dizziness, fatigue, and reduced activity tolerance. Incorporating active standing into clinical as-sessment could aid early identification of autonomic dysfunction and inform rehabili-tation strategies, though more research is urgently needed.