['Lifestyle intervention is not always effective for improving arterial hypertension and other cardiovascular risk factors, and the parameters determining the outcome are not known. Because high cardiorespiratory fitness (CRF) protects from cardiovascular disease and mortality, we determined whether CRF at baseline predicts the improvement of blood pressure and other cardiovascular risk factors during a lifestyle intervention.', 'A total of 219 patients at risk for type 2 diabetes, who underwent a 9-month lifestyle intervention with diet modification and increase in physical activity, and had measurement of CRF, were studied. Insulin sensitivity was estimated during a 75-g oral glucose tolerance test. Total body, visceral and liver fat were measured by magnetic resonance (MR) tomography and H-MR spectroscopy. CRF was estimated using two different methods, an incremental cycle exercise (maximal aerobic capacity-VO2max) test and a motorized treadmill (individual anaerobic threshold) test.', 'After 9 months of intervention adiposity, glycemia, CRF, insulin sensitivity, SBP and serum lipids (except high-density lipoprotein cholesterol, P = 0.65) improved (all other P ≤ 0.006). DBP did not change significantly (P = 0.06). High CRF at baseline predicted decreases in SBP (P ≤ 0.0002) and DBP (P ≤ 0.004), and increase in insulin sensitivity (P ≤ 0.04), but not change in serum lipids (all P ≥ 0.06). For 1 SD increase in baseline CRF the odds ratio for resolution of hypertension or prehypertension was 2.26 (individual anaerobic threshold; 95% CI 1.40-3.80) and 1.75 (VO2max; 95% CI 1.08-2.89).'] Does cardiorespiratory fitness determine the reduction in blood pressure and insulin resistance during lifestyle intervention?