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


METHODS
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.


RESULTS
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).


CONCLUSIONS
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.
Pérez-Martin
A
A
Service Central de Physiologie Clinique, Unité CERAMM, Centre d'Exploration et de Réadaptation des Anomalies Métaboliques et Musculaires, Cedex 5, France. a-perez_martin@chu-montpellier.fr
Dumortier
M
M
Raynaud
E
E
Brun
J F
JF
Fédou
C
C
Bringer
J
J
Mercier
J
J
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D004734:Energy Metabolism; D005080:Exercise Test; D005260:Female; D006801:Humans; D007328:Insulin / Q000097:blood; D007773:Lactates / Q000097:blood; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology / Q000503:physiopathology; D009765:Obesity / Q000378:metabolism / Q000503:physiopathology*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D005082:Physical Exertion / Q000502:physiology*; D012016:Reference Values; D015203:Reproducibility of Results; D012146:Rest
D001786:Blood Glucose; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D007328:Insulin; D007773:Lactates