Summary
Purpose: The aim of the study was to compare the outcomes of patients with post-COVID-19 condition undergoing supervised therapeutic exercise intervention or following the self-management WHO (World Health Organization) rehabilitation leaflet.
Methods: A randomized controlled trial was carried out that included 39 participants with post-COVID-19 condition who had a chronic symptomatic phase lasting >12 weeks. Comprehensive medical screening, patient-reported symptoms, and cardiorespiratory fitness and muscular strength were assessed. Patients were randomly assigned to a tailored multicomponent exercise program based on concurrent training for 8 weeks (two supervised sessions per week comprised resistance training combined with aerobic training [moderate intensity variable training], plus a third day of monitored light intensity continuous training), or to a control group which followed the WHO guidelines for rehabilitation after COVID-19.
Results: After follow-up, there were changes in physical outcomes in both groups, however, the magnitude of the change pre-post intervention favored the exercise group in cardiovascular and strength markers: VO2 max +5.7%, sit-to-stand -22.7% and load-velocity profiles in bench press +6.3%, and half squat +16.9%, (p < 0.05). In addition, exercise intervention resulted in a significantly better quality of life, less fatigue, less depression, and improved functional status, as well as in superior cardiovascular fitness and muscle strength compared to controls (p < 0.05). No adverse events were observed during the training sessions.
Conclusion: Compared to current WHO recommendations, a supervised, tailored concurrent training at low and moderate intensity for both resistance and endurance training is a more effective, safe, and well-tolerated intervention in post-COVID-19 conditions.

Relevance
The beneficial physiological adaptations to cardiopulmonary and skeletal muscle associated with a tailored concurrent training may be an effective, safe, and well‐tolerated intervention in post‐COVID‐19 conditions. Improvements in the quality of life, mood disorder symptoms, and cardiovascular and strength fitness suggest that exercise could have a main role in recovering active life when suffering long‐term disability because of post‐COVID‐19 conditions. There is an urgent need to explore other exercise‐based treatment strategies that could, together with neurocognitive and behavioral strategies, provide greater benefits for these patients.