Measurement properties of the 30-second sit-to-stand test in post COVID-19 condition: Results from the PYCNOVID randomised controlled trial
Julia Braun, Julia Kopp, Lisa Künzi, Milo A Puhan, Jan S Fehr, Thomas Radtke
Abstract
Background
The 30-second sit-to-stand test (30s-STS) is a frequently used measure of functional capacity in post-COVID-19 condition (PCC), but its measurement properties have not been comprehensively investigated.
Introduction
Post-COVID-19 condition (PCC) is a multisystem disease caused by severe acute respiratory syndrome coronavirus-19 (SARS-CoV-2) infection. The prevalence of PCC in the general population is estimated at ~6–7% with major implications for healthcare systems and the economy [1]. The pathophysiology of PCC remains incompletely understood. Proposed pathomechanisms include viral persistence, immune dysregulation, inflammation, endothelial and mitochondrial dysfunction, and microbiome dysbiosis, with combinations of these processes likely contributing to disease development and progression [2,3].
Methods
2.1. Study design and setting
Data were collected as part of the PYCNOVID trial [20]. This randomised controlled trial investigated the effects of a nutritional supplement with antioxidative and anti-inflammatory properties on health status (primary endpoint) in people with PCC. Notably, this parent study was not designed to improve functional capacity; it was a secondary endpoint in the main trial, which may have limited responsiveness and anchor validity.
Results
One-hundred fifty-three participants were randomised at the baseline visit and were included in the primary study. The 30s-STS test was available for 152 participants at screening (99.3%), 150 participants at baseline (98.0%), and 144 participants at study end (94.1%). Table 1 and S1 Table present characteristics of all participants who performed a 30s-STS at baseline.
Discussion
This study evaluated the measurement properties of the 30s-STS test in a large and heterogeneous sample of adults with PCC and high symptom burden. Following key findings emerged. First, the 30s-STS test was feasible and safe to administer, demonstrated good test-retest reliability, and showed no evidence for a learning effect. However, measurement error and between-subject variability can influence test results and should be considered when interpreting 30s-STS results.
Acknowledgments
We kindly thank the whole study team for their valuable work and commitment to the study. Moreover, we thank Dara Corina Spies Rodriguez for her support with data monitoring, data cleaning, and data preparation. We also thank the people with lived experience from the Long COVID Citizen Science Board for their input on study design and all institutions and healthcare professionals who supported us with participant recruitment. Most importantly, we thank all study participants for their time, effort, and willingness to contribute to this research.
Citation: Braun J, Kopp J, Künzi L, Puhan MA, Fehr JS, Radtke T (2026) Measurement properties of the 30-second sit-to-stand test in post COVID-19 condition: Results from the PYCNOVID randomised controlled trial. PLoS One 21(5): e0348275. https://doi.org/10.1371/journal.pone.0348275
Editor: Mukhtiar Baig, King Abdulaziz University Faculty of Medicine, SAUDI ARABIA
Received: February 4, 2026; Accepted: April 13, 2026; Published: May 12, 2026
Copyright: © 2026 Braun et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: All relevant data are within the paper and its Supporting Information files.
Funding: The study was funded by Horphag Research, Av. Louis-Casaï, 1216 Cointrin, Switzerland. The funder of the study had no role in study design, data collection, data analysis, data interpretation, and writing of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
