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Background: To determine the trustworthiness of graded exercise test to exhaustion (GXT) to assess maximal oxygen uptake (V˙O2max) in metabolic syndrome individuals with obesity and poor cardiorespiratory fitness. Methods: V˙O2max was assessed in 100 metabolic syndrome adults (57 ± 8 years; 34% women), with obesity (BMI 32 ± 5 kg·m−2) using GXT followed by supramaximal constant‐load verification test (VerT) at 110% of maximal GXT work rate. V˙O2 data from GXT and VerT were compared using paired t test and plotted for Bland‐Altman analysis. GXT sensitivity and specificity to detect V˙O2max were also calculated. Results: Seventy individuals did not achieve V˙O2 plateau during GXT. GXT underestimated V˙O2max in 40 subjects. In these subjects, the magnitude of V˙O2max underestimation with GXT was 9% (167 mLO2·min−1; P <.001). In the whole sample (n = 100), bias error differences between GXT and VerT was 63 mLO2·min−1 (3% underestimation). This error was constant regardless of differences in fitness levels among individuals (R = −0.07; homoscedasticity). GXT results were unreliable in 62% of the sample with 16% of false‐positive and 46% of false‐negative results. Sensitivity and specificity of GTX to assess V˙O2max were low (ie, 23% and 60%, respectively). Conclusion: Our data indicate that the magnitude (3%‐9%) and prevalence (40% of subjects) of V˙O2max underestimation with the use of a GXT alone is high in a large sample of unfit metabolic syndrome individuals with obesity. Our data advocate for the need of using VerT after GXT to avoid significant cardiorespiratory fitness underestimation in metabolic syndrome individuals with obesity and low fitness level. [ABSTRACT FROM AUTHOR]