Magnitude and determinants of change in objectively-measured physical activity, sedentary time and sleep duration from ages 15 to 17.5y in UK adolescents: the ROOTS study

Table 1 Characteristics of participants with valid PA and sedentary time data at baseline and follow-up

	Boys (n = 72)		Girls (n = 72)
	Baseline	Follow-up	Baseline	Follow-up	P-value (follow-up vs baseline, boys and girls combined)	P-value for gender × wave interaction
Age (y)	15.1 ± 0.3¹	17.4 ± 0.3	15.1 ± 0.3	17.5 ± 0.3	-	-
Weight (kg)	58.5 ± 10.2	68.1 ± 13.0	55.7 ± 8.2	59.8 ± 8.5	<0.001	<0.001
Height (cm)	171.8 ± 7.9	177.7 ± 6.7	163.1 ± 6.0	165.1 ± 6.0	<0.001	<0.001
BMI (kg/m²)	19.3 (3.3)²	20.8 (3.5)	20.4 (4.1)	21.3 (3.7)	<0.001	0.013
BMI z-score³	−0.030 ± 1.0	0.058 ± 1.1	0.19 ± 1.1	0.17 ± 1.0	0.47	0.27
Fat mass (kg)	7.6 (4.3)	9.1 (5.2)	14.6 (6.4)	15.4 (7.2)	<0.001	0.27
Fat mass index (kg/m²)	2.6 (1.4)	3.0 (1.6)	5.4 (2.4)	5.6 (2.5)	<0.001	0.65
Fat-free mass (kg)	49.7 (9.0)	55.5 (8.4)	40.8 (5.6)	43.2 (4.8)	<0.001	<0.001
Fat-free mass index (kg/m^2.5)	16.7 (1.8)	17.7 (1.9)	15.2 (1.6)	15.7 ± 1.4	<0.001	<0.001
Waist circ. (cm)^3,4	74.3 (6.6)	77.5 (9.1)	74.0 (12.2)	74.9 (10.5)	<0.001	0.043
Waist circ. z-score³	0.81 ± 0.72	0.75 ± 1.0	1.6 ± 1.0	1.7 ± 1.1	0.70	0.18
PAEE (kJ/kg/d)	83.1 ± 20.9	80.9 ± 23.1	62.3 ± 18.5	60.0 ± 19.8	0.19	0.98
LPA (min/d)	542.0 ± 105.4	557.0 ± 114.2	502.2 ± 107.7	490.9 ± 125.4	0.83	0.12
MPA (min/d)⁵	55.9 (31.9)	50.6 (34.7)	34.8 (30.6)	27.0 (25.1)	0.039	0.53
VPA (min/d)⁵	19.1 (29.7)	12.9 (21.3)	2.1 (6.4)	1.7 (6.3)	0.0038	0.0087
MVPA (min/d)⁵	79.5 (53.5)	67.5 (54.5)	37.6 (37.0)	31.3 (32.9)	0.0074	0.62
ST (min/d)	338.3 ± 110.4	324.4 ± 129.0	407.8 ± 118.7	403.9 ± 123.4	0.34	0.59
SLP (min/night)	478.0 ± 45.7	487.2 ± 54.8	486.3 ± 50.2	508.7 ± 59.8	0.0046	0.23

¹Mean ± SD (all such values); ²Median (IQR) for all variables with skewed distributions; ³Based on British growth reference data; ⁴Due to missing data based on 140 participants (69 boys and 71 girls); ⁵Baseline estimates differ from Collings et al. (2014) due to different summary statistics, here, to complement the normally distributed change variables, median and IQRs are preferred to the geometric mean; analyses performed using mixed-model ANOVA, there were few minor changes in results when the natural log of skewed variables were used as the dependent variable or when school clustering was accounted for by using multilevel regression; there were also no differences in p-values when the statistics for activity variables were adjusted for baseline age and FMI, ethnicity, area-level SES, follow-up duration, the total and weekend hours of monitor wear time and the seasons (school terms) of activity measurements at baseline and follow-up. LPA, light physical activity; MPA, moderate physical activity; MVPA, moderate-to-vigorous physical activity; PAEE: physical activity energy expenditure; SLP, sleep duration; ST, sedentary time; VPA, vigorous physical activity

ISSN: 1479-5868