Sex disparities in body composition trends among elementary school students based on grade

Modern lifestyle changes have contributed to developments and advances in almost all spheres of a child's life. However, negative consequences such as hypokinesia and obesity are also present. This study aimed to examine the differences in body composition parameters between boys and girls in higher elementary school grades. The sample consisted of 484 school-aged boys and girls from grades V to VIII in Knjaževac. The municipality of Knjaževac represents a group of municipalities with up to 30,000 inhabitants, a municipality of that size based on the number of inhabitants is 49.6% of the total number of municipalities in the Republic of Serbia.

An anthropometer (SECA model 284; SECA, Hamburg, Germany) and a body composition analyzer (InBody 770, InBody Co, Seoul, Korea) were used to collect the measured parameters.

Using ANOVA, with the addition of post hoc analysis, a statistically significant trend was determined across all analyzed body composition parameters, namely, skeletal muscle mass (SMM), body fat mass, lean body mass (LBM), and relative lean body mass (RLBM) (p < 0.001, p = 0.049, p < 0.001, and p < 0.001, respectively), except for relative body fat mass (RBFM) (p = 0.145), in children of both sexes from grades V to VIII. A significant trend was observed among the boys for SMM, RSMM, LBM, RLBM (p < 0.001), and RBFM (p = 0.004), while among the girls, a significant trend was noted for SMM and LBM p < 0.001).

Sex-related differences in muscle mass and body mass were clearly observed. In the male subjects, there was a significant increase in relative muscle mass, while in the female subjects, there was a statistically significant increase in body fat percentage. These findings highlight the necessity of taking sex differences into account when monitoring and analyzing body composition parameters in children.