The authors declare no conflicts of interest.

Objective: To determine whether regular physical activity influences the prevalence of obesity in children. Methods: This study includes a sample of 239 students representing 45 % of the population of 531 students of 1st Cycle of Santarém District, Portugal (public school). Ages ranging between 6 and 12 years and 50.6 % belong to the female gender. Body composition was measured (Height, Weight, Skinfolds, BMI and %Fat Mass); Results: When compared with previous studies in the same region, seems to indicate that this population has evolved positively in regard to the prevalence of obesity and the prevalence of overweight, as well as indicate lower values than those presented by international studies specifically WHO data between 2002 and 2009. Conclusions: most individuals do regular physical activity within or outside the school, and 14.5 % are those who never practice it. It can be said that all the students have or make a conscious “effort”, preferring the "good food " like fruit and vegetables several times a day