C74-17 Blunted Muscle Oxygen Extraction in Association With Exercise Capacity Under Long Covid

Background

Long COVID is defined as the persistence of symptoms for at least three months following SARS-CoV-2 infection, with exercise intolerance being one of its most prevalent manifestations. Recent studies reported that long COVID individuals have lower peak oxygen consumption (VO2), suggesting reduced aerobic capacity. However, it remains unclear whether this reduction reflects impaired skeletal-muscle oxidative metabolism or limitations in respiratory muscle function. Assessing muscle-specific oxygenation responses, particularly in the vastus lateralis (VL), a superficial quadriceps knee extensor commonly monitored during exercise, and the intercostal muscles (IC), which reflect respiratory muscle oxygenation, may help elucidate the underlying mechanism. This study aims to explore the association between muscle oxygenation responses and exercise capacity, and to determine whether these relationships differ in individuals with long COVID.

Methods

People recovered from SARS-CoV-2 were recruited. Individuals with a confirmed diagnosis of cardiac, pulmonary, or musculoskeletal disease or disorder affecting exercise capacity were excluded. Participants were divided into long COVID and non-long COVID groups based on the WHO clinical case definition. Exercise capacity was assessed by VO2 measured at the end of exercise (VO₂peak) using a symptom-limited ergometry test (CPET). Peripheral skeletal muscle oxygenation was assessed by measuring muscle oxygen saturation (SmO₂), oxyhemoglobin (O₂Hb), and deoxyhemoglobin (HHb) in VL and IC using near-infrared spectroscopy (NIRS). Between-group differences were compared, and the relationship between exercise capacity and muscle oxygenation was examined.

Results

30 long COVID and 27 non-long COVID participants were recruited. Peak work rate was comparable between groups. The non-long COVID group demonstrated a higher VO₂peak than the long COVID group (24.12 ± 4.10 vs 21.83 ± 4.20 mL·kg⁻¹·min⁻¹, p < 0.05). No between-group differences were observed in IC oxygenation indices. In contrast, the long COVID group exhibited altered VL oxygenation kinetics, including smaller SmO₂ reductions from rest to anaerobic threshold (AT) and to peak exercise, and a blunted increase in HHb from AT to end-exercise (p < 0.05), suggesting reduced peripheral oxygen extraction at higher exercise intensities. Consistently, VO2peak is negatively associated with the magnitude of VL SmO₂ reduction during exercise. Hence, the reduced aerobic capacity in long COVID may reflect peripheral metabolic inefficiency rather than respiratory muscle oxygen metabolism.

Conclusion

Individuals with long COVID showed reduced aerobic capacity despite preserved respiratory muscle oxygenation. Altered VL oxygenation kinetics indicate impaired peripheral oxygen metabolism as a contributor to exercise intolerance in long COVID.

This abstract is funded by: the Health and Medical Research Fund (HMRF) - Commissioned Research on COVID-19 from the Health Bureau of Hong Kong Special Administrative Region (reference number COVID1903007).