INTRODUCTION:
Sarcopenia and obesity contribute to compromised bone quality and heightened fracture susceptibility in aging; yet, findings in individuals with frailty are equivocal. The present study examined bone microarchitecture variations among distinct body composition profiles in pre-frail and frail older adult women.

METHODS:
In this cross-sectional analysis, 109 met Fried's frailty criterion. Dual-energy X-ray absorptiometry (DXA) measured body composition, defining four groups: low appendicular lean mass (LALM; residuals <20th percentile, −1.45), obesity (fat mass index >13 kg/m²), combined obesity and LALM, or absence of both. High-resolution peripheral quantitative computed tomography (HR-pQCT) assessed bone microarchitecture. Analyses employed generalized estimating equations (GEE) adjusted by Bonferroni, alongside χ² and Fisher’s exact tests. Results. Obesity versus LALM groups exhibited improved bone microarchitecture in cortical area (Ct.Ar 90 vs. 71 mm²; age-adjusted P=0.008) and cortical thickness (Ct.Th 1.031[0.217] vs. 0.858[0.202] mm; P=0.043) at the tibia, with parallel enhancement at the radius (Ct.Ar 43 vs. 33 mm²; P=0.002; Ct.Th 0.779[0.157] vs. 0.642[0.175] mm; P=0.005). Obesity plus LALM, compared to LALM, showed higher lower Ct.Ar, Ct.Th, total volumetric bone density (Tt.vBMD), and trabecular number (Tb.N), along with greater trabecular area (Tb.Ar) and trabecular separation (Tb.Sp) at the radius. Both obesity groups demonstrated higher bone strength compared to LALM group. Conclusions. In older adult women with frailty, obesity linked to superior cortical and trabecular microarchitecture versus low muscle mass alone, implying adiposity's potential protective role against bone loss. Prospective research is needed to elucidate body composition's influence on fracture outcomes in frailty.