Physical Activity and Bone Accretion: Isotemporal Modeling and Genetic Interactions.

Area of Science:

• Pediatric bone health
• Exercise science
• Skeletal development

Background:

• Childhood and adolescence are critical periods for bone mineral density (BMD) and bone mineral content (BMC) accrual.
• Physical activity (PA) is a key determinant of skeletal health, with different types of activity potentially having varying effects.
• Understanding the specific impact of high- versus low-impact PA on pediatric bone health is crucial for developing effective interventions.

Purpose of the Study:

• To investigate whether substituting time spent in high-impact physical activity (PA) for low-impact PA, or vice versa, predicts changes in pediatric bone mineral density (BMD) and bone mineral content (BMC).

Main Methods:

• Analysis of longitudinal data from the Bone Mineral Density in Childhood Study (N=2337, ages 5-19).
• Calculation of Z-scores for areal BMD and total body less head (TBLH) BMC.
• Application of isotemporal substitution modeling to assess the impact of replacing hours of low-impact PA with high-impact PA, and vice versa, on bone outcomes.
• Testing for statistical interactions with sex, ancestry, age, and genetic predisposition to bone fragility.

Main Results:

• High-impact PA was positively associated with bone Z-scores across all measured skeletal sites.
• Low-impact PA showed no significant association with bone Z-scores.
• Replacing 1 hour/day of low-impact PA with high-impact PA was linked to significantly higher bone Z-scores.
• Conversely, replacing high-impact PA with low-impact PA was associated with lower bone Z-scores.
• These substitution effects were consistent across sex and ancestry but were more pronounced in older adolescents.

Conclusions:

• Time-sensitive models indicate that substituting low-impact PA with high-impact PA is beneficial for the growing skeleton in most children.
• This strategy can positively influence pediatric bone mineral density and content accrual.
• The findings support recommendations for prioritizing high-impact activities for optimal skeletal development in children and adolescents.