Consistent longitudinal patterns of lean mass development from childhood to young adulthood are associated with bone and muscle outcomes in early adulthood, with appendicular lean mass index more closely related to bone structure and muscle area, while a favorable muscle-to-fat ratio may reflect better muscle quality and whole-body bone status.
Key Findings
Results
Low appendicular lean body mass index (aLBMI) trajectory from childhood to young adulthood was associated with substantially lower bone mineral density at multiple skeletal sites in early adulthood.
Low aLBMI trajectory was associated with lower aBMD at the whole body less head (WBLH), femoral neck, and trochanter ranging from -8% to -11% compared to the average trajectory.
Linear regression was adjusted for sex and height, with the average trajectory serving as the reference group.
No differences in aBMD were observed at the radius for the low aLBMI group.
Sample included 116 participants with consistent aLBMI trajectories out of 323 total participants (aged 8-23 years) assessed at 7 time points.
Results
Low aLBMI trajectory was associated with substantially reduced tibial structural bone strength in early adulthood.
Low aLBMI trajectory was associated with reduced tibial structural strength ranging from -23% to -34% compared to the average trajectory.
Bone structure was assessed using pQCT geometry and strength measures at age 23 years.
No significant differences at the radius were noted for the low aLBMI group.
Assessments were conducted using both DXA (aBMD) and pQCT (vBMD, geometry, and strength).
Results
High aLBMI trajectory was associated with greater bone mineral density, bone strength, and muscle area in early adulthood.
Higher aLBMI trajectories were associated with higher aBMD up to +17% compared to the average trajectory.
Greater bone strength was observed in the tibia and radius, ranging from +22% to +45%.
Larger muscle area was associated with higher aLBMI trajectories at +32% compared to the average group.
Muscle composition was assessed using pQCT muscle area and muscle density at age 23 years.
Results
High appendicular lean mass to trunk fat mass ratio (aLBM/TrFM) trajectory was associated with higher whole-body bone mineral density but not with site-specific bone structural outcomes.
For aLBM/TrFM, only WBLH aBMD differed significantly, with the high group showing approximately 5% higher values compared to the average trajectory.
No significant differences were observed at other bone sites for aLBM/TrFM trajectories.
Analysis included 67 participants with consistent aLBM/TrFM trajectories.
The high aLBM/TrFM group also showed lower BMI and higher muscle density compared to other trajectory groups.
Methods
Only participants with consistent lean mass trajectories across all time points were included in the trajectory analyses, substantially reducing the analytic sample.
The total sample included 323 participants assessed at 7 time points between ages 8 and 23 years.
Only 116 participants had consistent aLBMI trajectories and were included in that analysis.
Only 67 participants had consistent aLBM/TrFM trajectories and were included in that analysis.
Lean mass trajectories were categorized as low, average, or high using DXA-derived Z-scores.
Data were drawn from the Iowa Bone Development Study.
Results
The aLBMI measure was more strongly associated with bone structural outcomes and muscle area, while the aLBM/TrFM ratio was more reflective of muscle quality and overall bone status.
aLBMI showed associations with bone structure (pQCT geometry and strength) at both the tibia and radius, and with pQCT muscle area.
aLBM/TrFM was associated only with WBLH aBMD (~5% higher in the high group) and with lower BMI and higher muscle density.
The authors interpret higher muscle density as a potential indicator of better muscle quality.
These two lean mass indices appear to capture distinct aspects of musculoskeletal health in early adulthood.
What This Means
This research suggests that the pattern of lean muscle mass development during childhood and adolescence has meaningful consequences for bone and muscle health in early adulthood. Using data from 323 participants followed from ages 8 to 23, researchers identified whether individuals consistently had low, average, or high lean mass relative to their peers. They found that young adults who consistently had low lean mass throughout childhood and adolescence had notably weaker bones—particularly in the hip and shin—by age 23, while those who consistently had high lean mass had stronger bones and larger muscles. The differences in bone strength were substantial, ranging from roughly 8–34% lower or 17–45% higher compared to those with average lean mass trajectories.
The study also looked at a different measure that accounts for the balance between muscle in the limbs and fat around the trunk. People with a consistently favorable muscle-to-fat ratio had slightly better whole-body bone density (about 5% higher) and better muscle quality, as measured by muscle density on imaging, even though their bones were not structurally larger or stronger at specific sites. This suggests that carrying less trunk fat relative to limb muscle may reflect a healthier overall body composition, independent of how much muscle mass a person has in absolute terms.
These findings suggest that maintaining adequate lean mass throughout the growing years—rather than just at one point in time—may be important for building strong bones and muscles that persist into early adulthood. This research supports the idea that childhood and adolescence represent a critical window for musculoskeletal development, and that consistent patterns of lean mass across those years, not just peak values, are relevant to long-term bone and muscle health.
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Marques M, Baptista F, Rysavy O, Pendleton C, Levy S, Janz K. (2026). Lean mass development trajectories in children and adolescents and their associations with musculoskeletal health in emerging adulthood.. Frontiers in endocrinology. https://doi.org/10.3389/fendo.2026.1898386