Effect of after-school physical activity on body composition in primary school children: The Slovak "PAD" project

Physical activity is associated with many physical and mental health benefits. This study aimed to investigate the effect of a 24-month after-school physical activity intervention on body composition in normal-weight children. Participating students (6-7 years of age at baseline) were divided by reason of their parental preference to intervention and control groups. Children in the intervention group (n = 20; 10 boys and 10 girls) followed an aerobic training program (two 60-min sessions per week), whereas children in the control group (n = 20; 10 boys and 10 girls) participated in the usual practice. Body composition characteristics were repeatedly measured by means of bioelectrical impedance method. At 2 years, finally, intervention boys had a smaller rise in BMI (mean difference, MD: -0.97 kg/m² , p < 0.05), BMI z-score (-0.44, p < 0.09), body fat % (BF%) (-6.47%, p < 0.01), and fat mass index (FMI) (-1.32 kg/m² , p < 0.001) than controls. In girls, however, the intervention program induced no significant differences (p > 0.9) in the measured variables compared to controls at the final follow-up (MD: -0.04 kg/m² for BMI and -0.01 for BMI z-score). Changes in BF% and FMI in a positive direction occurred at 18 months (MD: -3.38%, p < 0.05 and -0.99 kg/m² , p < 0.01, respectively), but did not persist over time (p > 0.07). In addition, no significant changes (p > 0.07) in the fat-free mass index were associated with the physical activity intervention in either boys or girls. In conclusion, compared to the controls, a long-term physical activity intervention in boys was associated with a significantly smaller rise in BMI and improvement of body composition by reducing both BF % and FMI. In girls, however, this intervention did not result in any statistically significant changes in body composition variables.