"The leanest and fittest kids are the ones who have the most vigorous activity for longer periods of time," says Dr. Bernard Gutin, exercise physiologist at the Medical College of Georgia and lead author on the study published in the April American Journal of Clinical Nutrition. "We could not show that the amount of minutes spent in moderate activity such as walking to school was related to how fat they were, although it did have some impact on cardiovascular fitness. The implication is that you need to do vigorous activity if you want to be lean."
Researchers used an accelerometer that discriminates between light, moderate and vigorous physical activity to monitor the usual physical activity of 421 black and white adolescents for five days. Cardiovascular fitness was measured by a treadmill test that went progressively faster at an increasing incline. The most fit took in more oxygen at a lower heart rate. Dual-energy X-ray absorptiometry, which measures bone, fat and fat-free soft tissue (mostly muscle) was used to determine body fat.
Adolescents averaged just five minutes per day of vigorous physical activity across the five days, with black males having the highest average at 8.6 minutes and black females the lowest at 2.8 minutes. They averaged nearly 40 minutes of moderate activity daily. Not surprisingly, boys had less body fat than girls, says Dr. Gutin. White and black females averaged 29.8 percent body fat and 30 percent respectively. Teenage girls should target at or below 25 percent, based on the accurate DXA measurement; over 30 percent body fat is considered obese.
" (T)hese data suggest that general exercise recommendations for adolescents should encourage vigorous physical activity," study authors write. However, to help ensure success, obese, unfit children should start with
Contact: Toni Baker
Medical College of Georgia