Objectively measured physical activity trajectories predict adolescent bone strength: Iowa Bone Development Study

Abstract

Background Physical activity improves bone strength and reduces the risk for osteoporotic fractures. However, there are substantial gaps in our knowledge as to when, how and how much activity is optimal for bone health. Purpose In this cohort study, we examined developmental trajectories of objectively measured physical activity from childhood to adolescence to discern if moderate-and-vigorous intensity physical activity (MVPA) predicts bone strength. Methods Starting at age 5 and continuing at 8, 11, 13, 15 and 17 years, Iowa Bone Development Study participants (n=530) wore an accelerometer for 3–5 days. At age 17, we assessed dual X-ray energy absorptiometry outcomes of mass and estimated geometry (femoral neck cross-sectional area and section modulus). We also assessed geometric properties (bone stress index and polar moment of inertia) of the tibia using peripheral computer quantitative tomography. Latent class modelling was used to construct developmental trajectories of MVPA from childhood to late adolescence. General linear models were used to examine the trajectory groups as predictors of age 17 bone outcomes. Results Girls and boys who accumulated the most MVPA had greater bone mass and better geometry at 17 years when compared to less active peers. The proportion of participants achieving high levels of MVPA throughout childhood was very low (<6% in girls) and by late adolescence almost all girls were inactive. Conclusions Bone health benefits of physical activity are not being realised due to low levels of activity for most youth, especially in girls.

Bone Densitometry in Children and Adolescents

“…The Iowa Bone Development Study (a prospective cohort study) showed 10% to 16% greater hip BMC and 8% greater hip areal BMD in participants who accumulated the greatest amount of activity from childhood through adolescence (12-year follow-up). 39 For patients with limited mobility, reducing immobility through physical therapy 40 or the use of vibrating platforms can be helpful. 29,41 Reducing inflammation, undernutrition, or hormone imbalances also is necessary.…”

Vertical Jump Test as a Health-Promotion Screening Tool for Predicting Bone Strength in Young Adults

“…Demographic characteristics of the IBDS subject population include being 95% white, with two-thirds of the subjects' parents having college degrees (Janz et al, 2014;Janz et al, 2015). This secondary analysis focuses on IBDS participants with assessments in early adulthood, specifically 18 to 22 year old males (n = 136, mean age 19.7±0.7 years) and females (n = 167, mean age 19.7±0.6 years).…”

“…Participants for the IBDS were recruited from 1998 to 2001, when subjects were approximately 5 years of age, from a larger group of Midwestern children (n = 890) that had been recruited and were already participating in the Iowa Fluoride Study (Janz et al, 2014;Janz et al, 2015). Original recruitment for the Iowa Fluoride Study occurred in eight Iowa hospitals from 1992 to 1995 immediately following birth.…”

“…The Iowa Bone Development Study (IBDS) is an ongoing, longitudinal study of bone health throughout childhood, adolescence, and young adulthood (Janz et al, 2014;Janz et al, 2015). Participants for the IBDS were recruited from 1998 to 2001, when subjects were approximately 5 years of age, from a larger group of Midwestern children (n = 890) that had been recruited and were already participating in the Iowa Fluoride Study (Janz et al, 2014;Janz et al, 2015).…”

“…Trained research staff conducted DXA scans for all participants using the Hologic QDR 4500A DXA (Delphi upgrade) with software V.12.3 in the fan-beam mode, as described previously (Janz et al, 2014). Briefly, software-specific Global Regions of Interest (ROI) were used to designate the general boundaries of the hip images.…”