Table 1. Summary of the main studies evaluating exercise intolerance in patients after COVID-19 infection.

Time of evaluation sample (n)	Dyspnea (mMRC)	Subgroups	Peak VO2 in the sample	Findings
Rinaldo et al. 2 3 months (n = 75)	57%	Severity of hospitalization: mild-moderate, severe, and critical	54% (VO2 < 85%prev) (post hoc analysis)	Older Greater residual pulmonary sequelae No difference in lung function No difference in peak VO2 in cardiocirculatory and gas exchange responses. Mild increase of V’E/V’CO2 in the critical vs. mild-moderate group
Rinaldo et al. 4 3 months (n = 75)	52%	Reduced or normal peak VO2	55% (VO2 < 85%prev)	Lower lactate threshold Lower ∆VO2/∆WR Lower pulse O2
Skjørten et al. 5 3 months (n=156) (multicenter)	47%	Comparison with normal population without COVID-19 by z-score (20% in ICU)	89 ± 17%prev 31% (VO2 < 80%prev)	15% reduced lactate threshold 16% ventilatory limitation 23% desaturation >4% 15% increased ∆V’E/∆V’CO2
Motiejunaite et al. 6 3 months (n = 114)	Dyspnea 40% Fatigue 32%	DCO ≤ or > 75%prev	75% (VO2 < 85%prev)	Smallest peak VO2 Lower lactate threshold Tendency to greater limitation to exercise
Liu et al. 12 7 months (n = 41)	-	Persistence or absence of pulmonary fibrosis on chest CT	16.4 ± 3.6 mL/kg/min (with fibrosis) 20.2 ± 3.7 mL/kg/min (no fibrosis)	Older and more severe hospitalization Smallest peak VO2 Lower METS Higher V’E/V’CO2
Debeaumont et al.* 6 months (n = 23)	78%	ICU vs. ward	52% (VO2 < 85%prev)	Higher ∆V’E/∆V’CO2
Dorelli et al.** 5 months (n = 28)	-	∆V'E/∆V’CO2 > 31 or ≤ 31	29.2 ± 8.3 mL/kg/min	No difference in pulmonary function variables at rest and in CPET responses

Abbreviations: mMRC: Medical Research Council modified dyspnea scale; peak VO₂: peak exercise oxygen consumption; WR: work rate; V’E/V’CO₂: minute ventilation by carbon dioxide output; DCO: carbon monoxide diffusion; chest CT: chest computed tomography; ICU: intensive care unit. *Https://www.doi.org/10.1093/ptj/pzab099 **DOI: https://www.doi.org/10.3390/diagnostics11030507.