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Credit to www.medscape.com

August 22, 2006 — High- vs low-intensity physical activity (PA) results in improved cardiovascular fitness and obesity in children, according to the results of a cross-sectional study reported in the August issue of the American Journal of Clinical Nutrition.

"It is unclear how the amount and intensity of physical activity (PA) are associated with cardiovascular fitness (CVF) and body fatness in children," write Jonatan R. Ruiz, MD, from Karolinska Institutet in Huddinge, Sweden, and colleagues. "High CVF during childhood and adolescence has been associated with a healthier cardiovascular profile not only during these years but also later in life."

In this study, 780 children aged 9 to 10 years from Sweden and Estonia underwent measurements of accelerometry, expressed as minutes per day of total PA, moderate PA, and vigorous PA. CVF as watts per kilogram was measured with a maximal ergometer bike test, and body fat was derived from the sum of 5 skin-fold-thickness measurements. Using multiple regression analysis, the investigators determined the degree to which variance in CVF and body fat was explained by PA, after controlling for age, sex, and study location.

Lower body fat was significantly associated with higher levels of vigorous PA, but not with moderate or total PA; children engaging in more than 40 minutes of vigorous PA per day had lower body fat than did those who engaged in 10 to 18 minutes of vigorous PA per day. Total PA, moderate PA, and vigorous PA were positively associated with CVF, but those children engaging in more than 40 minutes of vigorous PA per day had higher CVF than those who engaged in less than 18 minutes of vigorous PA per day.

"The results suggest that PA of vigorous intensity may have a greater effect on preventing obesity in children than does PA of lower intensity, whereas both total and at least moderate to vigorous PA may improve children's CVF," the authors write.

Study limitations include cross-sectional design preventing determination of causality; inability of the accelerometer to compensate for the relative increase in energy expenditure by increase in body size; and lack of generalizability to overweight and obese children.

"With regular reports of increasing childhood obesity prevalence worldwide, the results of this study are noteworthy," the authors conclude. "Although we controlled for several potential confounders, such as age, sex, and study location, other variables such as food intake and genetic aspects may also have an influence."

The Stockholm County Council, the Estonian Science Foundation, and the Estonian Centre of Behavioural and Health Sciences supported this study. The authors have disclosed no relevant financial relationships.

Am J Clin Nutr. 2006;84:299-303.

Learning Objectives for This Educational Activity

Upon completion of this activity, participants will be able to:

• Identify recommendations for PA for school-aged children.
• Compare different levels of PA in promoting fitness and appropriate weight in children.

Clinical Context

Overweight and obesity in children is a growing problem in developed countries, and there has been a fair amount of research focused on the role of PA in combating this problem. Strong and colleagues reviewed 850 articles regarding these issues in a systematic analysis published in the June 2005 issue of the Journal of Pediatrics. While most research focused on the health benefits of exercise between 30 and 45 minutes per day in a controlled environment, the authors assessed that a longer period of practicing at least moderate PA in an unsupervised setting would be necessary to derive the same health benefit as found in the research studies. Therefore, they concluded that children should spend at least 60 minutes per day engaged in moderate or vigorous PA. Brisk walking, bicycling, and active outdoor playing are considered examples of moderate activity.

The current study addresses the role of intensity of PA in levels of physical fitness and body fat in children.

Study Highlights

• Study subjects were drawn from the European Youth Heart Study, which occurred in Sweden and Estonia. All participants were between the ages of 9 and 10 years.
• Body mass index was calculated for all subjects, and body fat was estimated by skin-fold-thickness measurements at 5 body locations. CVF was measured by maximum exertion on a cycle ergometer and was reported in watts per kilogram of body mass. PA was assessed on 4 consecutive days by means of an activity monitor attached to the subject's hip. Moderate PA was defined by activity requiring 3 to 6 metabolic equivalents of energy, while vigorous activity expended more than 6 metabolic equivalents of energy.
• The main study outcome was the association between PA and both CVF and body fat. These results were adjusted for sex, chronologic age, and study location.
• 780 children provided data for analysis. The mean age of subjects was 9.5 years old, and the mean body mass index was 16.9 kg/m². The average durations of moderate and vigorous exercise per day were 170.9 and 26.3 minutes, respectively.
• Girls exhibited lower CVF and greater percentages of body fat than boys. They were also less physically active than boys.
• The average daily duration of vigorous PA had a significant negative effect on the percentage of body fat, whereas total or moderate PA did not.
• On the contrary, all forms of PA — total, moderate, and vigorous — positively influenced CVF.
• The levels of CVF and body fat had a significant inverse relationship.
• Among children who performed vigorous activity, mean daily duration of such activity exceeding 40 minutes was associated with reduced body fat vs subjects practicing 10 to 18 minutes of vigorous activity per day. CVF was superior among children performing at least 26 minutes of vigorous PA per day compared with those practicing 10 to 18 minutes of vigorous activity per day.

Pearls for Practice

• Previous recommendations have called for at least 60 minutes of daily moderate to vigorous PA for healthy children.
• In the current study, only vigorous PA was associated with a significant negative effect on body fat in children, but both moderate and vigorous PA improved CVF