TREUTH, M. S., N. F. BUTTE, A. L. ADOLPH, and M. R. PUYAU. A Longitudinal Study of Fitness and Activity in Girls Predisposed to Obesity. Med. Sci. Sports Exerc., Vol. 36, No. 2, pp. 198–204, 2004.
Purpose: To determine whether physical activity and fitness change in girls with and without a predisposition to obesity from 8 to 10 yr of age.
Methods: Normal-weight girls (N = 91) were recruited at 8 yr of age according to parental body mass index (BMI): LN = girls with two lean (BMI < 25 kg·m−2) parents, LNOB = girls with one obese and one lean parent, and OB = girls with two obese (BMI > 28 kg·m−2) parents. A longitudinal study was undertaken with annual assessments at 8, 9, and 10 yr of age. The primary outcomes were fitness (V̇O2peak) measured by treadmill testing, and physical activity measured by heart rate monitoring and by questionnaire. Sedentary behavior was assessed by questionnaire.
Results: V̇O2peak (mL·kg−1·min−1) did not change over time; however, V̇O2peak (L·min−1 and mL·kg−1·min−1), time on the treadmill, and treadmill stage were different across groups (P < 0.02). Girls with LNOB parents had a lower absolute V̇O2 than the LN girls by 2.5 mL·kg−1·min−1 (P < 0.05). The OB group had a 3.9 mL·kg−1·min−1 lower V̇O2 than the LN group (P < 0.001). The girls of LN parents also exercised longer on the treadmill (P < 0.05) than girls with OB parents. The percent of the day spent active on the weekday and weekend did not change over time or between groups. Time spent watching TV during the school year and summer was similar over the study period and between groups.
Conclusion: Our data suggest that fitness and physical activity remain fairly constant in girls from 8 to 10 yr of age, but girls of obese parents tend to be less fit.
The increasing prevalence of obesity in children in the United States has been well documented (19,29). In 6- to 11-yr-old girls, 27.8% are overweight or at risk of overweight (19). At risk of developing obesity are children of obese parents, where parental obesity more than doubles the risk of adult obesity among children <10 yr of age (34).
The Report of the Surgeon General on Physical Activity and Health (31) emphasized that regular physical activity has important health benefits including reducing the risk of cardiovascular disease and helping to treat and prevent high blood pressure, high cholesterol, and diabetes. Physical activity has been promoted as a lifelong positive health behavior in children and adolescents (5). However, approximately 20% of U.S. children do not exercise vigorously more than twice per week, with the percentages higher in girls (26%) than in boys (17%) (1). Participation in physical activity declines with increasing age in children, particularly in girls (5,21,31). Recently, a report from The National Heart, Lung, and Blood Institute Growth and Health Study (15), found substantial declines in physical activity in girls from 9 or 10 to 18 and 19 yr of age. A higher body mass index was one correlate of this decline. Whether physical activity begins to decline in girls from 8 to 10 yr of age has not been thoroughly investigated.
Fitness is another important factor related to health outcomes, independent of physical activity. Several cross-sectional studies (17,33) have reported fitness levels in girls ranging in age from 7 to 13 yr. However, longitudinal studies examining age-related changes in fitness in young girls are few. A positive relationship between obesity and fitness has been reported (20).
We enrolled multiethnic, normal-weight 8-yr-old girls with or without a predisposition to obesity into a longitudinal study. Predisposition to obesity was defined by parental body mass index (BMI) with LN = girls with two lean (BMI < 25 kg·m−2) parents, LNOB = girls with one obese and one lean parent, and OB = girls with two obese (BMI > 28 kg·m−2) parents. This study was designed to determine whether physical activity, fitness, and sedentary behaviors change in girls from 8 to 10 yr of age and if these changes are different based on whether or not the girls were predisposed to obesity.