Heterogeneity in Relation of Body Composition from BIA and DXA to handgrip strength and isokinetic knee strength

Objective This study aimed to simultaneously evaluate the relationship between body composition assessed by dual-energy X-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA) with muscle strength in the same cohort of community-dwelling adults, and to compare the associations of these two modalities for handgrip and lower limb muscle strength. Methods A total of 94 community-dwelling adults (59 women, 35 men) aged ≥40 years underwent body composition assessment using DXA and BIA, along with isokinetic knee strength and handgrip strength measurements. Correlation and multiple linear regression analyses were performed to examine associations between body composition parameters and muscle strength, stratified by sex where appropriate. Results In the fully adjusted models (age, BMI, and sex), BIA-derived parameters remained significantly associated with handgrip strength (e.g., UEFFM: β = 0.646, p < 0.001; FFM: β = 0.428, p < 0.05), whereas most DXA-derived parameters were no longer significant. For knee extensor strength, DXA-derived appendicular and leg-specific lean mass indices remained significant (ALM: β = 0.579, p < 0.01; LELM: β = 0.510, p < 0.01), while among BIA parameters only FFM remained significant (β = 0.542, p < 0.05). For knee flexor strength, both DXA- and BIA-derived parameters showed significant associations (e.g., DXA ALM: β = 0.551, p < 0.01; BIA FFM: β = 0.650, p < 0.01). Segment-specific analyses revealed that lower limb strength correlated more strongly with leg-specific lean mass, while handgrip strength showed closer associations with arm-specific measures. Conclusion After adjustment for age, BMI, and sex, BIA and DXA showed modality-specific associations with muscle strength. BIA was more strongly associated with handgrip strength, whereas DXA-derived height-adjusted indices were more strongly associated with lower limb strength. These findings support the tailored use of BIA and DXA in functional assessment, although neither method directly measures skeletal muscle mass.