Peripheral Oxygen Extraction Is Reduced During Submaximal Exercise in Post-COVID-19 Condition

Studies in post-COVID-19 condition following hospitalisation have focused on maximal exercise, with limited insight into submaximal responses that better reflect daily activities. We compared central haemodynamic, ventilatory, and peripheral muscle oxygen extraction responses during submaximal exercise between individuals with post-COVID-19 condition and healthy age-matched controls.

Twelve participants with post-COVID-19 condition, who were assessed 624 (593, 729) days following hospitalisation (median (IQR) length of stay: 7 (4.7, 11.7) days) and seven age-matched healthy controls (59±11 years) completed a 4-min constant-load exercise test at 80% of peak cycling workload. Cardiac output (CO), oxygen uptake (V̇O₂), and ventilatory efficiency (V̇E/V̇CO₂) were assessed throughout exercise. Arteriovenous oxygen content difference was calculated using the Fick equation (C(a-v)O₂ = V̇O₂/CO).

Post-COVID-19 condition participants exhibited a lower (p=0.03) mean±SD C(a-v)O₂ compared with healthy controls (135±29 vs. 171±46mLO₂·L⁻¹ blood). No significant differences were observed between post-COVID-19 condition and controls for V̇O₂ (1.9±0.3 vs. 2.1±0.7L·min⁻¹), V̇_E/V̇CO₂ (26.6±3.0 vs. 27.5 ± 2.4), or CO (12.7± 3.0 vs. 11.1± 3.6L·min⁻¹), indicating similar central cardiovascular and ventilatory responses between groups, despite a numerically greater cardiac output in the post-COVID-19 condition group (11±4% higher). In contrast, RER and V̇E/V̇O₂ were significantly higher in healthy controls than in post-COVID-19 condition participants, indicating divergent ventilatory behaviour despite preserved V̇E/V̇CO₂.

Post-COVID-19 condition following hospitalisation is characterised by reduced peripheral oxygen extraction during submaximal exercise, alongside no significant difference in cardiovascular responses and preserved ventilatory efficiency with respect to carbon dioxide elimination, compared with healthy controls. Although RER and V̇E/V̇O₂ were higher in healthy controls, indicating some divergence in ventilatory behaviour between groups, this did not reflect impaired ventilatory efficiency in post-COVID-19 condition. These findings indicate that differences in exercise responses at workloads representative of daily living are possibly peripheral rather than central, supporting rehabilitation strategies targeting skeletal muscle oxidative function.