A six-year longitudinal study of the relationship of physical activity to bone mineral accrual in growing children: The University of Saskatchewan bone mineral accrual study
Da. Bailey et al., A six-year longitudinal study of the relationship of physical activity to bone mineral accrual in growing children: The University of Saskatchewan bone mineral accrual study, J BONE MIN, 14(10), 1999, pp. 1672-1679
To investigate the influence of physical activity on bone mineral accrual d
uring the adolescent years, we analyzed 6 years of data from 53 girls and 6
0 boys. Physical activity, dietary intakes, and anthropometry were measured
every 6 months and dual-energy X-ray absorptiometry scans of the total bod
y (TB), lumbar spine (LS), and proximal femur (Hologic 2000, array mode) we
re collected annually. Distance and velocity curves for height and bone min
eral content (BMC) were fitted for each child at several skeletal sites usi
ng a cubic spline procedure, from which ages at peak height velocity (PHV)
and peak BMC velocity (PBMCV) were identified. A mean age- and gender-speci
fic standardized activity (Z) score was calculated for each subject based o
n multiple yearly activity assessments collected up until age of PHV. This
score was used to identify active (top quartile), average (middle 2 quartil
es), or inactive (bottom quartile) groups. Two-way analysis of covariance,
with height and weight at PHV controlled for, demonstrated significant phys
ical activity and gender main effects (but no interaction) for PBMCV, for B
MC accrued for 2 years around peak velocity, and for BMC at 1 year post-PBM
CV for the TB and femoral neck and for physical activity but not gender at
the LS (all p < 0.05). Controlling for maturational and size differences be
tween groups, we noted a 9% and 17% greater TB BMC for active boys and girl
s, respectively, over their inactive peers 1 year after the age of PBMCV. W
e also estimated that, on average, 26% of adult TB bone mineral was accrued
during the 2 years around PBMCV.