Balance of substrate oxidation during submaximal exercise in lean and obese people.

To compare fat and carbohydrate oxidation at different exercise intensities between overweight and normal-weight subjects, in order to analyze the influence of muscular metabolic abnormalities in obese people on substrate utilization during exercise.32 healthy sedentary overweight subjects (Body Mass Index (BMI): 30.8 +/- 0.8 kg/m(2); body fat: 37.4 +/- 1.1%; mean +/- SEM) and 26 controls (BMI: 23 +/- 0.4 kg/m(2); body fat: 22.7 +/- 1.1%) matched for age and sex were examined. The test consisted in four six-min. submaximal steady-state workloads with calculation of substrate oxidation rates and derived quantitative parameters, i.e., crossover point (defined as the power at which carbohydrate-derived energy becomes predominant) and maximal fat oxidation rate point. In addition, the accuracy of the test was analyzed and was found to be satisfactory.While exercise intensities were similar in both group, fat oxidation rates were significantly lower in overweight group (p<0.05). The crossover and the maximal fat oxidation rate points were significantly lower in overweight subjects than in controls: 33.3 +/- 2 vs 50.1 +/- 3.4% and 30.5 +/- 2.3 vs 44.6 +/- 3.3% of maximal aerobic power, respectively (p<0.001).Sedentary overweight subjects, compared to controls at the same exercise intensities, exhibited an alteration of the balance of substrate oxidation, reflected by lower rates of fat oxidation and a shift of quantitative parameters to lower intensities. The test appeared to be reliable and could be of interest to advise an individualized exercise prescription in obese people.