BACKGROUND: Low cardiorespiratory fitness (CRF) is a risk factor for many chronic diseases. This study aimed to evaluate the CRF of a sample of adults with different glucose tolerance statuses to explore its relationship with early abnormal glucose metabolism according to sex. METHODS: A total of 93 participants were assigned to three groups, i.e. the normal glucose tolerance (NGT) group, impaired glucose regulation (IGR) group and new-onset type 2 diabetes mellitus (T2DM) group, through an oral glucose tolerance test. Cardiopulmonary exercise testing was performed to evaluate the participants' CRF. The physical measurements (including height, weight, systolic blood pressure [SBP] and diastolic blood pressure) and laboratory test results (including fasting plasma glucose and two-hour plasma glucose [2h-PG]) of all participants were collected. Partial correlation, multiple linear regression (stepwise method) and logistic regression were used to analyse the data. RESULTS: Compared to the males with NGT, those with T2DM or IGR had a lower exercise time (P=0.044), anaerobic threshold (AT) oxygen uptake (VO<
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2<
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) (P=0.009), maximum VO<
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2<
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/kg (P=0.041) and oxygen uptake efficiency slope (P=0.002). The male participants with T2DM had lower AT power (P=0.001) than those with IGR or NGT. Compared to the females with NGT, the AT heart rate (HR) (P=0.003), AT SBP (P=0.002) and maximum VO<
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2<
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/kg (P=0.039) were lower in the female T2DM and IGR groups. The multiple linear regression (stepwise method) analyses showed that the maximum VO<
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2<
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/kg (β=-0.268, P=0.026) and one-minute HR recovery (β=-0.239, P=0.039) of the females improved the prediction of the 2h-PG when entered in the model. The logistic analysis results indicated that the VO<
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2<
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max of the male participants was related to pre-diabetes (β=-0.003, P=0.024) and that their AT power was associated with new-onset diabetes (β=-0.053, P=0.010). Meanwhile, the AT SBP of the female participants was related to pre-diabetes (β=0.120, P=0.019), and their AT HR was related to new-onset diabetes (β=-0.102, P=0.014). CONCLUSIONS: Low CRF is associated with abnormal glucose metabolism. The CRF is closely associated with the 2h-PG after glucose load and is an important risk factor for pre-diabetes and new-onset diabetes.