MINERVA MEDICA COPYRIGHT ® Relationship between physical activity and obesity in children and adolescents Aim. The purpose of the present study was to analyze the rela- tionship between physical activity (PA) and obesity in Portuguese children and adolescents. Methods. The sample consisted of 1 341 children and adolescents (8-15 years of age), 634 males (age, 10.6±2.3 y; body mass, 40.6±12.7 kg; height, 1.431±1.41 m) and 707 females (age, 10.9±2.4 y; body mass, 50±12.4 kg; height, 1.428±1.32 m). The sample was divided into quartiles of percentage of body fat (%BF) and phys- ical activity index (PAI), within age and gender. Children in the upper %BF quartile were defined as obese (arbitrary definition). Logistic regression for each PAI quartile was used to determine the odds ratio of obese children and adolescents (≥P75 of %BF) in comparison to their non-obese counterparts (<P75 of %BF). Results. Males in the lowest PAI quartile have an odds ratio of 2.1 of having obesity in relation to males in the highest PAI quartile. For females any significant result was found between PAI quartiles. Conclusion. The results obtained in this study add some data to the controversy of PA and obesity relationship youth. Logistical regression shows that males who have a lower PAI have an odds ratio of 2.1 of obesity, in comparison with males that have higher PAI. Those findings were not found in girls. KEY WORDS: Physical fitness - Obesity - Child - Adolescence. O besity is considered as one of the main public health problems with epidemic proportions in children and adolescents in industrialized countries. 1 Even in recent industrialized countries the prevalence of obesity is high. 2 Thus, childhood obesity is emerg- ing rapidly as a global epidemic, with profound con- sequences in public health. Obesity during childhood and adolescence is supposed to be an important deter- minant of whether a subject will become obese as an adult. 3 An important fact is that, independently of adults’ weight, adults that were obese children have a higher cardiovascular diseases morbidity and mortal- ity. 4, 5 Besides heredity, which is known as the major fac- tor in the development of obesity in pediatric years, the endocrine and metabolic disturbances are also point- ed out as causes of obesity with significant impact. 6 The cultural background, socio-economical level, energy consumption and physical inactivity have also been recognized as obesity determinants. 7, 8 Some authors suggest that there is an interaction between genetic and environmental factors. 9 However, the increasing prevalence of overweight and obesity must be caused by environmental factors, because genes have not changed for thousands of years, 10 and physical inac- tivity may be a key factor. 11 In several countries where an increase in the prevalence of obesity occurred, some 1 Faculty of Sports Science and Physical Education University of Porto, Porto, Portugal 2 Faculty of Medicine, University of Porto, Porto, Portugal 3 Institute for Exercise and Sport Sciences University of Copenhagen, Copenhagen, Denmark This study was supported by grant FCT: PSAU/122/96 and FC Gulbenkian 48988/2001. Address reprint requests to: Dr. J. Mota, Research Centre in Physical Activity, Health and Leisure, Faculty of Sports Science and Physical Education, University of Porto, Rua Dr. Plácido Costa 91, 4200 450 Porto, Portugal. E-mail: jmota@fcdef.up.pt S. GUERRA 1 , A. TEIXEIRA-PINTO 2 , J. C. RIBEIRO 1 , A. ASCENSÃO 1 , J. MAGALHÃES 1 , L. B. ANDERSEN 3 , J. A. DUARTE 1 , J. MOTA 1 Vol. 46 - No. 1 THE JOURNAL OF SPORTS MEDICINE AND PHYSICAL FITNESS 79 BODY COMPOSITION, SPORT NUTRITION AND SUPPLEMENTATION (ERGOGENICS) ORIGINAL ARTICLES J SPORTS MED PHYS FITNESS 2006;46:79-83