Table 1.

Characteristics of the participants.

	Age 5 yr		Age 13 yr		Age 15 yr
	Boys (n = 156)	Girls (n = 170)	Boys (n = 143)	Girls (n = 160)	Boys (n = 114)	Girls (n = 117)
Ht (cm)	112.3 (5.7)*	111.0 (5.4)	163.0 (9.8)**	160.1 (6.6)	175.4 (8.2)**	163.9 (6.5)
Wt (kg)	20.5 (3.7)	20.0 (3.8)	57.3 (15.9)	55.3 (14.2)	69.1 (14.3)**	61.2 (14.2)
Spine BMC (g)	16.1(2.4)*	15.4 (2.4)	41.7 (11.4)**	47.0 (11.0)	60.1 (13.7)	57.8 (10.8)
Hip BMC (g)	7.1 (1.6)	6.9 (1.3)	27.6 (7.8)*	25.7 (5.3)	37.8 (8.8)**	29.5 (5.7)
MVPA (min/day)	59.1 (23.8)**	47.1 (19.8)	51.5 (24.5)**	32.9 (17.4)	38.2 (19.4)**	25.8 (15.4)
≥ 60 min MVPA/day (%)	44.0	25.0	31.0	8.0	11.0	3.0
Vigorous PA (min/day)	13.0 (9.3)**	10.0 (7.1)	16.8 (12.6)**	9.3 (8.6)	10.9 (10.8)**	6.7 (6.9)
Monitor wear (days)	4.0 (0.3)	4.0 (0.3)	4.9 (0.6)	4.9 (0.8)	4.5 (1.0)	4.6 (0.9)
Monitor wear per day (min)	732.4 (41.8)	733.3 (42.7)	746.0 (52.7)	754.6 (62.0)	737.4 (72.8)	736.3 (72.5)

Values are presented as mean (SD).

Untransformed MVPA and Vigorous PA minutes reported here; Box-Cox transformed values used in all inferential analyses.

BMC, bone mineral content; MVPA, moderate and vigorous-intensity physical activity; PA, physical activity.

^*p < 0.05,

^**p < 0.01 Student’s t-test of boys vs. girls.