Physical activity (PA) during childhood and adolescence is important for the accrual
of maximal peak bone mass. The precise dose that benefits bone remains unclear as
methods commonly used to analyze PA data are unsuitable for measuring bone‐
relevant PA. Using improved accelerometry methods, this study identified the
amount and ...
Physical activity (PA) during childhood and adolescence is important for the accrual
of maximal peak bone mass. The precise dose that benefits bone remains unclear as
methods commonly used to analyze PA data are unsuitable for measuring bone‐
relevant PA. Using improved accelerometry methods, this study identified the
amount and intensity of PA most strongly associated with bone outcomes in 11–12‐
year‐olds. Participants (n = 770; 382 boys) underwent tibial peripheral quantitative
computed tomography to assess trabecular and cortical density, endosteal and
periosteal circumference and polar stress‐strain index. Seven‐day wrist‐worn raw
acceleration data averaged over 1‐s epochs was used to estimate time accumulated
above incremental PA intensities (50 milli‐gravitational unit (mg) increments from
200 to 3000 mg). Associations between time spent above each 50 mg increment and
bone outcomes were assessed using multiple linear regression, adjusted for age, sex,
height, weight, maturity, socioeconomic position, muscle cross‐sectional area and
PA below the intensity of interest. There was a gradual increase in mean R2 change
across all bone‐related outcomes as the intensity increased in 50 mg increments
from >200 to >700 mg. All outcomes became significant at >700 mg (R2
change = 0.6%–1.3% and p = 0.001–0.02). Any further increases in intensity led to a
reduction in mean R2 change and associations became non‐significant for all outcomes >1500 mg. Using more appropriate accelerometry methods (1‐s epochs; no a
priori application of traditional cut‐points) enabled us to identify that ~10 min/day
of PA >700 mg (equivalent to running ~10 km/h) was positively associated with
pQCT‐derived measures of bone density, geometry and strength in 11–12‐year‐
olds.