Background: SB and PI have been independently associated with deleterious metabolic outcomes, however evidence on the combined effects of SB, PA, and CRF in insulin sensitivity are scarce. Further research is also needed on the optimal type of activity to replace SB. Aim: To examine the independent and combined effects of SB, PA, and CRF in insulin sensitivity and to investigate whether reallocating ST with different activity types can improve insulin sensitivity in people with MetS. Methods: A cross-sectional analysis was performed in 64 subjects with MetS aged 40 to 65 years old. MetS was determined based on NCEP ATP III criteria and hyperinsulinaemic-euglicaemic clamp technique was used to assess the whole-body insulin sensitivity (M-value). SB and PA were measured with a hip-worn tri-axial accelerometer and VO_2max (ml/kg/min) with a maximal cycle ergometer test. The independent associations were provided with Pearson´s correlation and the combined associations with stepwise multiple linear regression. Forced-entry multiple linear regression was employed for the SB replacement analysis. Results: 58% of the sample were women, most subjects had high WC, BP, and FPG levels, and 48% had insulin resistance. Around 10.0 h/day were spent in SB, 29 breaks were performed during ST, and 1.8 h/day were spent in standing posture. An additional 1.7 h/day and 1.0 h/day were spent in LPA and MVPA, respectively, however participants showed a very poor CRF. Overall, men had a poorer metabolic and insulin profile (WC, HDL, FPG, FPI, HOMA-IR, M-value), greater SB proportion, and performed less breaks while women presented a higher body fat percentage and lower VO_2max levels. SB was independently and strongly associated with higher WC, FPI, and HOMA-IR whereas standing time was strongly correlated with lower FPI and HOMA-IR and greater M-value. A strong relationship was also found between VO_2max and BMI, body fat and fat free percentages. Standing time and MVPA showed synergic effects in FPI and HOMA-IR while the combined standing time and VO_2max were associated with greater M-value. Moreover, the replacement of ST with standing time showed significant improvements in FPI and HOMA-IR whereas frequent breaks and standing time significantly improved M-value. Conclusion: Less ST, more breaks, and greater PA time and CRF were independently associated with a healthier BMI and metabolic and insulin profile, while the combined standing time and MVPA and standing time and VO_2max were associated with greater effects in the insulin profile. Reallocating ST with standing time showed significant improvements in the insulin markers. These findings provide a broader understanding of the SB, PA, and CRF effects in the cardiometabolic health and indicate possible strategies to attenuate the deleterious effects of SB in populations with metabolic disorders.