Daily Physical Activity, Body Fat and Aerobic Fitness in Children

Sammanfattning: Introduction: Physical inactivity, low aerobic fitness and obesity are all associated with an increased risk of a wide range of diseases in adults. Promotion of physical activity, improvement of aerobic fitness and regulation of body weight in children may be of importance, as low physical activity, low aerobic fitness and obesity early in life have been known to track into adulthood. However, relationships between physical activity, obesity and aerobic fitness have not been studied in young subjects with reliable methods. The aim was to evaluate objectively daily physical activity and investigate if any relation existed with obesity and aerobic fitness in a cohort of children aged 8-11 years. Furthermore, the aim was to investigate gender differences and the determinants of aerobic fitness. Method:Two hundred and forty eight children, aged 8-11 years, participated. Physical activity was assessed with accelerometers. Body composition was quantified with dual-energy x-ray absorptiometry. Maximal oxygen uptake (VO2PEAK) was measured by indirect calorimetry during a maximal cycle ergometer exercise test. Echocardiography was performed with 2-dimensional guided M-mode and left ventricular inner diastolic diameter (LVDD) was measured. Lung function was evaluated with spirometric testing. Results: All children studied reached the current recommendation for physical activity. Children with a higher percentage of body fat were significantly less active. A positive relationship was established between daily physical activity and aerobic fitness. Boys had between 8-18% higher values than girls for VO2PEAK, dependent upon whether VO2PEAK was expressed in absolute values or scaled to body mass, lean body mass or if allometric scaling was used. In multiple regression analysis absolute values of VO2PEAK were independently related to lean body mass, maximal heart rate, gender, LVDD and daily accumulation of vigorous activity. Conclusions: In this cohort of children aged 8-11 years all individuals fulfilled the current daily physical activity recommendation. Despite this, relationships between daily physical activity vs. obesity and aerobic fitness were detected. Furthermore, gender differences in aerobic fitness were confirmed and the main determinants of aerobic fitness were identified.