A single bout of submaximal aerobic functional capacity test acutely promotes endothelial function in long COVID patients

Persistent symptoms and vascular impairment are common among individuals recovering from COVID-19, yet little is known about acute interventions capable of improving endothelial function in this group. Submaximal functional tests, such as the six-minute step test (6MST), provoke marked cardiovascular activation and may provide a brief stimulus for vascular adaptation. This study examined whether performing a single 6MST session could trigger an immediate enhancement in brachial artery endothelial function in adults with long COVID. Forty-seven participants, symptomatic long COVID individuals and healthy controls, underwent evaluations of respiratory function, fatigue, dyspnoea, habitual physical activity, and functional capacity. Cardiorespiratory responses during the 6MST were measured with a portable metabolic system, and flow-mediated dilation (FMD) of the brachial artery was assessed before exercise and 10–15 min afterward. At baseline, the long COVID group demonstrated greater adiposity, a higher burden of comorbidities, reduced functional capacity, lower peak V̇O2, and attenuated FMD relative to controls. A single bout of submaximal test acutely improves brachial artery endothelial function in individuals with persistent symptoms following COVID-19. These participants also displayed reduced functional capacity and peak VO2, greater diastolic blood pressure response, and increased lower limb fatigue during the test. Although VO2 peak showed a modest association with the FMD% response in univariate analysis, this relationship did not persist after adjustment for confounders, indicating that the acute vascular improvement was not independently determined by cardiorespiratory fitness.