Objective assessment of childhood adherence to Canadian physical activity guidelines in relation to body composition

Low levels of childhood physical activity (PA) are a contributing factor to obesity. The objective of this study was to determine the adherence of children to PA guidelines in relation to body composition. Body fat (Slaughter equation) and body mass index (BMI) were determined during the school year (n = 251, ages 8-11 y). Daily energy expenditure (EE, kcal.kg-1.d-1) and activity time (AT, min.d-1) above moderate and vigorous intensity thresholds were assessed (accelerometry). Using EE criteria, 35.9% expended < 3.0 kcal.kg-1.d-1, 27.9% expended between 3.0 and 5.9 kcal.kg-1.d-1, 13.5% expended between 6.0 and 7.9 kcal.kg-1.d-1, and 22.9% expended >or= 8.0 kcal.kg-1.d-1. Using AT criteria, 52.2% accumulated < 30.0 min, 31.1% accumulated 30.0-59.9 min, 12.7% accumulated 60.0-89.9 min, and 4.0% accumulated >or=90.0 min of AT. The EE corresponding to accumulation of AT > 90 min was 14.8 kcal.kg-1.d-1. The AT corresponding to >or= 8 kcal.kg-1.d-1 was 73.0 min. Inverse relationships were observed between EE and body fat (p = 0.0004), BMI (p = 0.002), mass (p = 0.008), and fat mass index (FMI) (p = 0.001), as well as between AT and body fat (p = 0.001), BMI (p = 0.008), mass (p = 0.017), and FMI (p = 0.002). Controlling for BMI, FMI was inversely related to EE (p = 0.049) and AT (p = 0.039). Fat-free mass index and AT were positively related (p = 0.038). Physical activity had beneficial effects on body composition for children independent of BMI. The relationship between AT and daily EE guidelines was rationalized (60 min.d-1 with 8 kcal.kg-1.d-1) and demonstrated association with acceptable body composition. The 60 min.d-1 of moderate activity may be a more suitable initial target than 90 min.d-1, as so few children met the upper tiers of PA guidelines.