Correcting for Fat Mass Improves DXA Quantification of Quadriceps Specific Strength in Obese Adults Aged 50–59 Years

Abstract 

Dual-energy X-ray absorptiometry (DXA) is widely used for bone mineral density and body composition assessments. However, DXA is known to overestimate muscle mass in obese adults. We used single-slice CT (ssCT) to derive a correction factor to enhance accuracy of DXA estimation of specific strength (strength per unit muscle). One hundred and sixty-two adults (age: 55.0±2.7yr, range: 50–59) were enrolled in this cross-sectional study and divided into groups based on body mass index (BMI: <30, 30–35, and ≥35). BMI groups did not differ in age, knee extensor strength (KES), thigh lean mass by DXA, or quadriceps cross-sectional area (CSA) by ssCT. Specific strength (KES/CSA) correlated with an uncorrected estimate of DXA–specific strength (r=0.82, 0.53, 0.84 and 0.74, 0.59, 0.57, p<0.001) in the lowest to highest BMI groups in men and women, respectively. Stronger correlations were achieved through correcting for BMI, age, and sex in estimating DXA—specific strength (r=0.81, 0.79, and 0.96 in the lowest to highest BMI groups in men and 0.94, 0.81, 0.85 in women, p<0.0001). Quantification of knee extensor—specific strength by DXA in men with BMI >30 and all BMI groups in women greatly improved using a correction factor for DXA estimates of thigh lean mass.

Key Words: CT, dual-energy X-ray absorptiometry, fat-free mass, knee extensor strength, obesity, specific strength