Abstract
BACKGROUND: Patients severely affected by post-COVID-19 condition (PCC) and myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) often experience long-term work incapacity, contributing to a growing economic burden. Organ-centered clinical diagnostics frequently fail to explain their work disability. OBJECTIVES: We aimed to objectively assess physical work ability using cardiopulmonary exercise testing (CPET) in a cohort of long-standing and severely affected PCC patients. We hypothesized: (1) patients with ME/CFS exhibit lower peak oxygen uptake (VO₂(peak) [mL/min/kg]) and peak power output (PPO [W/kg]) than those without; (2) most patients demonstrate objective work disability, closely aligned with subjective perception of disability; (3) oxygen pulse (O(2) pulse [mL/bpm]) is reduced in ME/CFS, independent of comorbidity. METHODS: The study was conducted in the Department of Sports Medicine, Prevention and Rehabilitation at Johannes Gutenberg-University Mainz (Mainz, Germany). Between July 31, 2023, and March 31, 2025, a total of 92 PCC patients with suspected occupational disease underwent symptom-limited CPET and completed the Canadian Consensus Criteria, Bell Disability Scale (Bell-Score), and DePaul Symptom Questionnaire (Post-Exertional Malaise) Short Form (DSQ-PEM). RESULTS: Nearly half of the patients (49%) met ME/CFS criteria and 79% screened positive on the DSQ-PEM. ME/CFS patients showed significantly lower VO₂(peak) (13.0 ± 3.1 vs. 15.4 ± 4.9, p = 0.012), PPO (0.9 ± 0.3 vs. 1.1 ± 0.5, p = 0.014), and O₂ pulse (7.7 ± 2.0 vs. 8.5 ± 1.9, p = 0.047) compared to those without ME/CFS. Overall, 66% of patients met objective thresholds for work disability (VO₂(peak) < 15 mL/min/kg or PPO < 1 W/kg). Forty-five patients (51%) had a Bell-Score ≤ 30 and 82% from those had VO₂(peak) < 15 and/or PPO < 1. VO₂(peak) and PPO significantly correlated with Bell-Score (r = 0.3, p = 0.005 and r = 0.3, p = 0.003) and were the lowest among patients on medical sick leave (13.3 ± 3.3 and 0.9 ± 0.3), compared to those in occupational reintegration (16.0 ± 3.9, p = 0.04 and 1.2 ± 0.5, p = 0.024) or currently working (18.0 ± 7.1, p = 0.036 and 1.2 ± 0.5, p = 0.015). CONCLUSIONS: Severely affected PCC patients exhibit objective work disability, particularly those with ME/CFS. VO₂(peak) and PPO are associated with subjective disability and occupational status. Therefore, early integration of CPET into clinical and occupational evaluations can inform individualized therapy planning and return-to-work decisions. Trial registration DRKS, DRKS00032394. Registered 28 July 2023, https://drks.de/search/de/trial/DRKS00032394.