For Obese Children, Lower Intensity Exercise Could Yield Increased Weight Loss

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Main Category: Obesity / Weight Loss / Fitness
Also Included In: Pediatrics / Children's Health;  Sports Medicine / Fitness
Article Date: 07 Apr 2008 - 0:00 PDT

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Obese children who wish to lose their excess weight most effectively will have better results if they focus on less intense exercise, according to a study of prepubescent boys released on April 1, 2008 in the BMJ Specialty Journal the British Journal of Sports Medicine.

Fitness is sometimes measured using the VO2 max, sometimes referred to as aerobic capacity, a n indication of a patient's body's ability to transport and utilize oxygen during strenuous exercise. It is determined by measuring the amount of oxygen absorbed in comparison to the amount of carbon dioxide expired per minute during physical exercise. The "Fat Max" was used in this study, defined as the level of exercise at which the oxidation of fat is highest, which is determined by analyzing the oxygen consumption of the body.

The researchers focused on this rate of fax burning, or oxidation, during graded leg cycling exercises in thirty boys of age 12. 17 of the children were obese, while the remaining 13 were lean and healthy. The exercises increased in intensity every 3.5 minutes, with a goal of finding the level of exercise intensity that would be most effective to burn off the most fat, the Fat Max.

The results indicated that the average peaks for oxygen consumption in fat oxidation for each group were considerably different. The lean boys were able to burn more fat than the obese boys at a higher exercise intensity. For the former, a peak level was reached around 50% exercise intensity, though there was still some improvement up through 60%. In contrast, the obese boys reached the same level at 30%, which is considered a low exercise intensity level. By the time they had reached the 50% intensity, the oxidation levels fell considerably, indicating that they would not burn off more fat.

In summary, the obese boys reached their optimal levels of fat oxidation, at the Fat Max, at much lower levels of exercise intensity than the lean boys. Additionally, more intense levels of exercise did not help them to burn more fat.

According to the authors, this might happen because obesity and a sedentary lifestyle can reduce muscle capacity, additionally diminishing its ability to use fat as a fuel. Obesity can also influence the type of muscle that is built -- obese people have more type 2 "fast twitch" muscle fibers, which are more effective at burning carbohydrates. In contrast, lean people have more type 1 muscle fibers, which are more effective at burning fat.

Comparison of fat oxidation during exercise in lean and obese pubertal boys: clinical implications
G Zunquin, D Theunynck, B Sesboue, P Arhan, D Bougle
Br J Sports Med 2008; 0: 1-3.
doi:10.1136/bjsm.2007.044529
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Written by Anna Sophia McKenney
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