Mechanical Load-Capacity Models for Bone in Youth - Analysis of Risk Signatures.

Low appendicular lean soft tissue index (ALSTI) was strongly associated with higher odds of low whole-body bone mineral density less head (WBLH BMD) in both sexes.

• Girls with low ALSTI had OR=3.9 for low WBLH BMD (p < 0.001)
• Boys with low ALSTI had OR=4.5 for low WBLH BMD (p < 0.001)
• ALSTI was used as a structural lean mass indicator (appendicular lean soft tissue index)
• Low values were defined as Z-scores ≤ -1, standardised by sex and age group

Low handgrip strength (HGS) was associated with higher odds of low WBLH BMD in both adolescent boys and girls.

• Girls with low HGS had OR=3.1 for low WBLH BMD (p < 0.001)
• Boys with low HGS had OR=4.5 for low WBLH BMD (p < 0.001)
• HGS was assessed with a dynamometer and used as a functional lean mass indicator
• Low HGS was defined as Z-score ≤ -1 standardised by sex and age group

Low HGS relative to body mass was associated with arms/legs BMD imbalance in both sexes, with a notably stronger association in girls than boys.

• Boys with low HGS/body mass had 1.8 times higher odds of low arms/legs BMD (p = 0.012)
• Girls with low HGS/body mass had 4.0 times higher odds of low arms/legs BMD (p < 0.001)
• Arms/legs BMD imbalance was used as an additional bone mechanical capacity indicator
• The sex difference in effect size suggests girls may be more vulnerable to functional lean mass deficits affecting regional BMD

The study analysed cross-sectional NHANES data from 5,424 adolescents aged 10-19 years collected between 2011 and 2020.

• Sample included both sexes aged 10-19 years
• Data were drawn from NHANES cycles collected between 2011 and 2020
• ALST, trunk fat mass, and BMD were determined using whole-body dual-energy X-ray absorptiometry (DXA)
• All variables were standardised by sex and age group using Z-scores, with Z ≤ -1 indicating low or at-risk values

Both structural lean mass (ALSTI and ALST/trunk fat mass) and functional lean mass (HGS and HGS/body mass) indicators were associated with bone mechanical capacity in adolescents.

• Structural lean mass was represented by ALSTI and the ratio of ALST to trunk fat mass (TrFM)
• Functional lean mass was represented by HGS and HGS/body mass ratio
• Bone mechanical capacity was represented by WBLH BMD and arms/legs BMD imbalance
• Findings reinforce the importance of lean soft tissue in bone health monitoring in youth