An 8-Year Longitudinal Analysis of Physical Activity and Bone Strength From Adolescence to Emerging Adulthood: The Iowa Bone Development Study

Abstract

Purpose: Most pediatric physical activity and bone health research has focused on the period immediately around puberty; few have addressed bone structural strength outcomes. This study assessed the magnitude and consistency of the longitudinal relationships between device-measured vigorous-intensity physical activity (VPA) and structural bone strength outcomes across adolescence to emerging adulthood.

Methods: Participants with 3 to 5 bone scans between the age of 11 and 19 years were studied (N = 439, 220 females, 1838 records). Dual-energy X-ray absorptiometry scans of the hip (hip structural analysis) and peripheral quantitative computed tomography scans of the tibia were obtained. Outcomes included femoral neck section modulus, femoral neck cross-sectional area, tibial Bone Strength Index, and tibial torsion strength (polar Strength Strain Index). Sex-specific bone mixed growth models were developed using biological age (chronological age - age at peak height velocity) as the time variable, and height, weight, and device-measured VPA as time-varying covariates. Models also included the VPA-biological age interaction.

Results: Individual-centered VPA and the VPA-biological age interaction were significantly, positively associated (P < .05) with Bone Strength Index, polar Strength Strain Index, section modulus, and cross-sectional area in males and females, indicating accumulative effects of VPA throughout maturation and beyond.

Conclusion: Bone remains responsive to the mechanical loading of physical activity throughout adolescence and into emerging adulthood. Attention should be placed on promoting bone-strengthening physical activity after the prepubertal years when adult exercise patterns are likely formed.

Keywords: adolescent; epidemiology; health.

Figure 1.

Growth models for Bone Strength Index (BSI, Panel A), Tibia Torsion Strength (pSSI, Panel B), Femoral Neck (NN) Section Modulus (Panel C), and NN Cross-Sectional Area (CSA, Panel D) aligned by Biological Age. BSI measured at the 4% site, and pSSI measured at the 38% site via Peripheral Quantitative Computed Tomography. NN Section Modulus and NN CSA measured via Hip Structural Analysis using Dual Energy X-Ray Absorptiometry. The red lines represent the 25^th percentile for mean VPA across adolescence, and the green lines represent the 75^th percentile for mean VPA across adolescence, highlighting their differences.