Objective assessment of physical activity (PA) using accelerometers and pedometers has become more accurate and common practice in the study of childhood overweight. The study aimed: i) to compare PA levels and body shape of boys and girls, and assess compliance of active children with the PA recommendation; ii) to analyse associations between the risk of overweight and the moderate-to-vigorous physical activity (MVPA) in children.

The sample comprised 395 children (198 girls) aged 6–10 years. Height and weight were measured, and BMI was calculated subsequently. A tri-axial accelerometer was used to obtain seven consecutive days of MVPA, as well as the weekly time being sedentary. Logistic regression analysis was used to examine the afore-mentioned relationship among the risk of obesity and MVPA, controlling for confounders.

After controlling for wearing time, boys spent significantly more minutes in the moderate-to-vigorous portion of PA than their female counterparts. About 47% of boys were active on week days by achieve the mean value of 60 min/day of MVPA; corresponding percentage for the weekend was just 32%. Among girls, only 22% were active on week days and 29% at the weekend. MVPA was not significantly associated with the risk of being overweight nor in female neither in male children. The final regression model revealed that girls of mothers with high educational level were less likely to be classified as overweight girls.

Findings revealed no significantly relation between MVPA and obesity risk among Portuguese children. Future research should extend similar design to other lifestyle features of children to clarify potential predictors of being overweight at early ages.