The Importance Of Age, Sex, BMI, And Movement Skills In Children’s Physical Activity Decline

Moderate-to-vigorous physical activity (MVPA) has been linked to several health benefits during childhood. Differences in MVPA exist among children of the same age and at different ages. As children grow in size, especially in body mass index (BMI), their MVPA may be adversely affected. Further, more proficient children in their fundamental movement skills (FMS) may be more active and have lower BMI. PURPOSE: to examine the relationships among age, sex, BMI, and FMS with children’s MVPA decline. METHODS: From the RUSH project, a random sample of 1,166 Portuguese children of both sexes aged 6-10 y from 36 schools were selected. BMI was calculated and transformed into z-scores (BMIz), and FMS (stationary dribble, kick, catch, overhand throw, underhand roll) were reliably assessed with the digital platform Meu Educativo. MVPA was objectively measured during 7 days with an Actigraph wGT3X-BT, and data were processed with the GGIR package. Multiple linear regression with a school clustering adjustment was used to examine the relationships, and the alpha was set at p < 0.05. RESULTS: On average, girls’ MVPA ranged from 73.4 min at 6 y to 62.3 min at 10 y, whereas in boys it ranged from 92.3 min at 6 y to 72.8 min at 10 y. BMI increased with age, and boys outperformed girls in FMS. Regression estimates showed that boys were systematically more active than girls (b = 9.77 ± 2.98 min) across age. With increasing age, MVPA declined (b = -5.89 ± 0.81 min), and this was constant in both boys and girls (the interaction age-by-sex was not significant: b = 0.16 ± 1.32). On average, children with higher BMIz had greater declines in MVPA (-1.46 ± 0.34 min), whereas those with higher FMS increased their MVPA (b = 4.01 ± 0.40 min). CONCLUSION: There was a systematic decline in primary school children’s MVPA from 6 to 10 y of age, and this pattern was constant in both boys and girls. Higher BMI was associated with lower MVPA, but children with higher FMS performance tend to be more physically active. La Caixa Foundation (reference: LCF/PR/SR1/52560017)