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

Background/Objectives: Individuals experiencing long COVID (LC) frequently report orthostatic 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 active standing orthostatic stress test in evaluating cardiovascular, autonomic, and respiratory responses in people experiencing LC. Methods: A systematic search, according 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 outcomes. Risk of bias was assessed using the nine-point Newcastle–Ottawa Scale. Results: Three studies (216 participants experiencing LC and 186 controls) met the inclusion criteria. Across studies, LC individuals consistently exhibited elevated heart rate in both supine and standing positions. However, blood pressure findings were more variable: only one study reported 13% of participants met orthostatic hypotension criteria, while another found significant increases in diastolic blood pressure during standing. Long COVID groups also showed reduced heart rate variability compared to controls. Conclusions: Individuals experiencing LC show elevated heart rate and impaired autonomic function during active standing, with subgroup-specific blood pressure changes. These alterations may contribute to dizziness, fatigue, and reduced activity tolerance. Incorporating active standing into clinical assessment could aid early identification of autonomic dysfunction and inform rehabilitation strategies, though more research is urgently needed.