Average annual change in sedentary time and in light and moderate and vigorous physical activity over three time points: baseline (age 9/10 years), +1 year (age 10/11 years) and +4 years (age 13/14 years)
| Sedentary (min) | Light intensity PA (min) | MVPA (min) | |||||||
|---|---|---|---|---|---|---|---|---|---|
| β Coefficient | 95% CI | p Value | β Coefficient | 95% CI | p Value | β Coefficient | 95% CI | p Value | |
| All days combined | |||||||||
| Age (years) | 10.6 | 9.1 to 12.2 | <0.001 | −8.9 | −10.1 to −7.8 | <0.001 | −3.9 | −4.8 to −3.0 | p<0.001 |
| Sex (reference category: boys) | |||||||||
| Girls | 13.1 | 8.8 to 17.4 | <0.001 | 11.0 | −4.7 to 26.7 | 0.168 | −37.59 | −49.9 to −25.3 | p<0.001 |
| Sex–age interaction (reference category: boys) | |||||||||
| Girls | −1.6 | −4.4 to 1.1 | 0.248 | −1.7 | −3.1 to −0.2 | 0.022 | 1.89 | 0.8 to 3.0 | p=0.001 |
| Weekdays | |||||||||
| Age (years) | 7.2 | 5.4 to 8.9 | <0.001 | −8.6 | −9.8 to −7.4 | <0.001 | −2.80 | −3.7 to −1.9 | <0.001 |
| Sex (reference category: boys) | |||||||||
| Girls | 17.2 | 12.9 to 21.5 | <0.001 | 7.71 | −8.2 to 23.7 | 0.343 | −34.0 | −46.3 to −21.7 | <0.001 |
| Sex–age interaction (reference category: boys) | |||||||||
| Girls | −2.1 | −5.0 to 0.8 | 0.152 | −1.5 | −3.0 to −0.1 | 0.037 | 1.5 | 0.4 to 2.6 | 0.009 |
| Weekend days | |||||||||
| Age (years) | 13.4 | 10.2 to 16.5 | <0.001 | −10.4 | −11.8 to −9.0 | <0.001 | −6.65 | −8.1 to −5.2 | <0.001 |
| Sex (reference category: boys) | |||||||||
| Girls | 50.6 | 4.4 to 96.8 | 0.032 | −3.5 | −7.0 to 0.1 | 0.052 | −46.6 | −67.3 to −25.9 | <0.001 |
| Sex–age interaction (reference category: boys) | |||||||||
| Girls | −4.2 | −8.4 to −0.1 | 0.047 | # | 2.8 | 1.0 to 4.7 | 0.003 | ||
Results are from three level mixed effects linear regression with levels: age, individual and baseline school. Participants with ≥2 time points are included in the models. Results are from models using activity outcomes derived for all days combined (n=990), and separately for weekdays (n=980) and weekend days (n=815). Age–sex interactions were tested for all models. β Coefficients represent the per year changes in the physical activity outcomes.
Interpretation: For the all days MVPA model, the average decrease per year of age is 3.9 min/day in boys and 2 min/day (ie, −3.9+1.9) in girls. At age 0, girls do on average 37.6 less min/day than boys, but at age 10 (approximately baseline) this would be (−37.6+10×(1.9)) 18.7 less and at age 14 this would be (−37.6+14×(1.9)) 11.1 less. #This model did not converge.
MVPA, moderate and vigorous physical activity; PA, physical activity.