title: 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+/-2.7 yr, range: 50-59) were enrolled in this cross-sectional study and divided into groups based on body mass index (BMI: <30, 30-35, and > or =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.
authors.affiliation: Department of Orthopaedics and Rehabilitation, The University of Iowa, Iowa City, IA 52242-1088, USA. neil-segal@uiowa.eud
authors.forename: Neil A
authors.initials: NA
authors.lastname: Segal
authors.forename: Natalie A
authors.initials: NA
authors.lastname: Glass
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Baker
authors.forename: James C
authors.initials: JC
authors.lastname: Torner
mesh_terms: D015502:Absorptiometry, Photon; D000367:Age Factors; D001823:Body Composition; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D009765:Obesity / Q000150:complications / Q000000981:diagnostic imaging / Q000503:physiopathology*; D011237:Predictive Value of Tests; D052097:Quadriceps Muscle / Q000503:physiopathology*; D015203:Reproducibility of Results