Are the Physically Active Adolescents Belonging to the »At Risk of Overweight« BMI Category Really Fat?

The adolescence is recognized as one of the critical periods for the development of obesity. Children and adolescents who practice sports regularly have higher muscle mass and lower percentage of body fat than their peers who are physically less active. Since body mass index (BMI) is a widely used indicator of overweight/obesity in spite of the fact that it directly measures excess in weight but not in fat, it often misclassifies athletic populations, both children and adults. The specific aim of this study was to evaluate whether BMI adequately assesses fatness in adolescents, especially physically active ones. The analysis was performed on anthropometric data from two surveys (1997 and 2009/2010) of Zagreb secondary school adolescents, 1315 girls and 1034 boys, aged 15–19 years. The group defined as »physically active« consisted of adolescents who practice organized sports (36.2% girls, 44.6% boys), while the »physically inactive« group was made of their peers who practice sport only as a part of physical education in schools. The standardized values, calculated within each sex by survey, were used for comparison of adolescents with different levels of physical activity. Physically active adolescents of both sexes had lower sum of skinfolds mean Z-values (pgirls<0.05, pboys<0.001); additionally, boys had higher Z-values for body weight (p<0.05) and triceps/subscapular ratio (indicating peripheral distribution of body fat) (p