SUMMARY OBJECTIVE: Patients with severe coronavirus disease 2019 (COVID-19) develop high muscle weakness. The objective of this study was to analyze the physical fitness of post-COVID-19 patients and its relationship with dyspnea and health-related quality of life (HrQoL). METHODS: This observational, retrospective, cross-sectional study was conducted between October and November 2021 in the Universidad Europea de Madrid (Spain), with 32 post-COVID-19 patients aged 63.2 (14.1) years. Muscle strength, aerobic capacity, maximal respiratory mouth pressures, dyspnea, and HrQoL were analyzed 6–12 months after discharge for COVID-19. To analyze the relationship between continuous variables, Spearman’s correlation test and Pearson’s correlation test were performed. RESULTS: The participants had a mean handgrip strength of 22.1 (9.0) kg and very poor HrQoL. Negative moderate correlations were found between handgrip strength and length of hospital and intensive care unit stay (r=−0.37; p=0.002). In addition, muscle strength was negatively correlated with dyspnea (r=−0.37; p=0.008) and HrQoL, and moderate-large negative correlations were found between dyspnea and HrQoL. CONCLUSION: Higher handgrip strength was associated with lower COVID-19 severity and less sequelae. Therefore, either the patients with severe COVID-19 suffered greater muscle breakdown, or higher muscle strength acted as a mitigating factor for the disease. It is suggested that post-COVID-19 rehabilitation programs should focus on increasing muscle strength. Also, adequate physical fitness could mitigate the physical and mental post-COVID-19 sequelae.