title: Sustained effects of physical activity on bone health: Iowa Bone Development Study.
abstract: Studies of youth athletics and interventions have shown some maintenance of bone mineral content (BMC; g) after cessation of training, but less is known about sustained effects of everyday physical activity (PA). Using a prospective cohort, this report examined potential effects of childhood PA on adolescent BMC. Participants (N=156 boys, 170 girls) had exams at ages 5, 13, and 15. Body size and maturity were determined using anthropometry. Moderate-to-vigorous-intensity PA (MVPA) and vigorous-intensity PA (Vigorous PA) were measured using accelerometry. BMC of the spine and hip was measured using dual-energy X-ray absorptiometry. Mixed regression models tested whether PA at age 5 affected BMC at ages 13 and 15 after adjustment for age (year), height (cm), weight (kg), maturity (pre-peak height velocity or post), and activity level (min/day). Analysis was repeated to control for age 5 BMC. On average, boys participated in 59, 52, and 38 min of MVPA and 13, 17, and 11 min of Vigorous PA at ages 5, 13, and 15, respectively. MVPA (β=0.799) and Vigorous PA (β=1.338) at age 5 predicted later spine BMC (p<0.05). MVPA (β=0.480) at age 5 predicted hip BMC. Girls participated in 47, 33, and 26 min of MVPA and 10, 9 and 7 min of Vigorous PA at ages 5, 13, and 15, respectively. Neither MVPA nor Vigorous PA predicted later spine BMC. MVPA (β=0.302) at age 5 predicted hip BMC. After controlling for BMC at age 5 as well as the other covariates, the effect of MVPA (β=0.695) and Vigorous PA (β=1.079) at age 5 remained significant for boys at the spine. For girls, neither MVPA nor Vigorous PA at age 5 predicted spine or hip BMC. Children's early PA appears to have a modest effect on adolescent BMC at the critical regions of spine and hip; benefits may be greater for geometric changes, which future studies should include.
authors.affiliation: Department of Health and Human Physiology, University of Iowa, Iowa City, IA, USA. Electronic address: shelby-francis@uiowa.edu.
authors.forename: Shelby L
authors.initials: SL
authors.lastname: Francis
authors.affiliation: Department of Epidemiology, University of Iowa, Iowa City, IA, USA.
authors.forename: Elena M
authors.initials: EM
authors.lastname: Letuchy
authors.affiliation: Department of Epidemiology, University of Iowa, Iowa City, IA, USA; Department of Preventive and Community Dentistry, University of Iowa, Iowa City, IA, USA.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Levy
authors.affiliation: Department of Health and Human Physiology, University of Iowa, Iowa City, IA, USA; Department of Epidemiology, University of Iowa, Iowa City, IA, USA.
authors.forename: Kathleen F
authors.initials: KF
authors.lastname: Janz
mesh_terms: D000293:Adolescent; D015519:Bone Density / Q000502:physiology*; D001846:Bone Development / Q000502:physiology*; D002648:Child; D002675:Child, Preschool; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007484:Iowa; D008297:Male; D011446:Prospective Studies; D012737:Sex Factors
keywords: Adolescence; Bone mineral content; Children; DXA; Longitudinal