Table 1. Description of study participants.

	Y8 (N = 94)	Y12 (N = 81)	Y19 (N = 71)
Mean age (SD), y	8.5(0.4)	11.9 (0.5)	19.3 (0.6)
Female: Male, N	46:48	39:42	35:36
Mean height (SD), cm
Female	131 (6)	152 (8)	165 (7)
Male	133 (7)	152 (8)	180* (7)
Mean weight (SD), kg
Female	28.5 (6.0)	42.0 (9.9)	60.8 (12.0)
Male	28.8 (5.5)	43.0 (10.7)	73.7* (17.2)
Mean BMI (SD)
Female	16.4 (2.5)	18.1 (3.3)	22.3 (4.3)
Male	16.1 (2.2)	18.5 (3.4)	22.8 (5.1)
LBP, % (95% CI)
All**	6 (2 to 13)	13 (7 to 23)	54 (42 to 66)
Female	9 (2 to 21)	8 (2 to 20)	56 (38 to 73)
Male	4 (1 to 15)	19 (9 to 34)	53 (35 to 70)

*p<0.001 according to sex

**p<0.001 for all participants according to age