Physical Activity and Bone Accretion: Isotemporal Modeling and Genetic Interactions

Jonathan A. Mitchell, Alessandra Chesi, Shana E. McCormack, Diana L. Cousminer, Heidi J. Kalkwarf, Joan M. Lappe, Vicente Gilsanz, Sharon E. Oberfield, John A. Shepherd, Andrea Kelly, Struan F.A. Grant, Babette S. Zemel

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


Purpose This study aimed to determine if replacing time spent in high- and low-impact physical activity (PA) predicts changes in pediatric bone mineral density (BMD) and content (BMC). Methods We analyzed data from the longitudinal Bone Mineral Density in Childhood Study (N = 2337 with up to seven visits). The participants were age 5-19 yr at baseline, 51.2% were female, and 80.6% were nonblack. Spine, total hip, and femoral neck areal BMD and total body less head (TBLH) BMC Z-scores were calculated. Hours per day spent in high- and low-impact PA were self-reported. Standard covariate-adjusted (partition model) and time allocation-sensitive isotemporal substitution modeling frameworks were applied to linear mixed models. Statistical interactions with sex, self-reported ancestry, age, and bone fragility genetic scores (percentage of areal BMD-lowering alleles carried) were tested. Results In standard models, high-impact PA was positively associated with bone Z-score at all four skeletal sites (e.g., TBLH-BMC Z-score: beta = 0.05, P = 2.0 × 10-22), whereas low-impact PA was not associated with any of the bone Z-scores. In isotemporal substitution models, replacing 1 h·d-1 of low- for high-impact PA was associated with higher bone Z-scores (e.g., TBLH-BMC Z-score: beta = 0.06, P = 2.9 × 10-15). Conversely, replacing 1 h·d-1 of high- for low-impact PA was associated with lower bone Z-scores (e.g., TBLH-BMC Z-score: beta = -0.06, P = 2.9 × 10-15). The substitution associations were similar for each sex and ancestry group, and for those with higher and lower genetic scores for bone fragility (P-interactions > 0.05), but increased in strength among the older adolescents (P-age interactions < 0.05). Conclusions Time-sensitive models suggest that replacing low-impact PA for high-impact PA would be beneficial for the growing skeleton in the majority of children.

Original languageEnglish (US)
Pages (from-to)977-986
Number of pages10
JournalMedicine and Science in Sports and Exercise
Issue number5
StatePublished - May 1 2018

All Science Journal Classification (ASJC) codes

  • Medicine(all)


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