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Soyang Kwon, Trudy L. Burns and Kathleen Janz

Background:

This study aimed to examine combined and independent effects of cardiorespiratory fitness and fatness on cardiovascular risk factors among U.S. adolescents.

Methods:

Data from adolescents age 12 to 19 years participating in the NHANES 1999 to 2002 were used. Fitness level was determined by submaximal treadmill test and was dichotomized as ‘not fit’ or ‘fit’ according to the FITNESSGRAM. Fatness level was categorized as ‘not fat’ or ‘fat’ based on the CDC BMI growth charts. Gender-specific multivariable linear regression analyses were conducted to compare age-, race/ethnicity-, fatness-, and waist circumference-adjusted means of blood pressure, lipids, lipoproteins, C-peptide, insulin, and C-reactive protein (CRP) levels.

Results:

A total of 3202 adolescents (1629 boys) were included for data analysis. Among boys, total cholesterol, tri-glycerides, insulin, and CRP mean levels were significantly higher (P < .05) in the ‘not fit’ group than in the ‘fit’ group, after adjustment for fatness level and waist circumference. Among girls, the fatness level- and waist circumference-adjusted means of total cholesterol (P < .01) and LDL-C (P < .09) were higher in the ‘not fit’ than ‘fit’ groups.

Conclusion:

Cardiorespiratory fitness, independent of fatness, may have beneficial effects on lipid profiles among girls, and on lipid profiles, insulin metabolism, and inflammation levels among boys.

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Soyang Kwon, Kathleen F. Janz, Trudy L. Burns and Steven M. Levy

The purpose of this study was to examine whether the association between daily light-intensity physical activity (LPA) and total body fat mass changes during childhood. The study sample was 577 children participating in the longitudinal Iowa Bone Development Study. Body fat mass and physical activity (PA) were measured using dual energy X-ray absorptiometry (DXA) and accelerometers, respectively, at approximately 5, 8, and 11 years of age. Age- and gender-specific multivariable linear regression models were fit to predict fat mass by LPA, adjusted for actual age, birth weight, fat-free mass, height, moderate- to vigorous-intensity PA, and physical maturity (only for girls). Among boys, LPA was negatively associated with fat mass at age 11, but not age 5 or 8. Among girls, LPA was negatively associated with fat mass at ages 8 and 11, but not at age 5. LPA may have a beneficial effect against excess adiposity among older children.