Can dual energy X-ray absorptiometry provide a valid assessment of changes in thigh muscle mass with strength training in older adults?

Objective: To determine how dual-energy X-ray absorptiometry (DXA) compares to computed tomography (CT) for measuring changes in total thigh skeletal muscle (SM) mass with strength training (ST) in older adults. Subjects: Fifty previously sedentary, relatively healthy older men (n = 23, 60 (s.d. = 7.5) years) and women (n = 27, 60 (s.d. = 9.3) years). Results: Results indicate that there was a significant increase in thigh SM mass with ST measured by both CT (3.97 +/- 0.4%) and DXA (2.97 +/- 0.6%) methods (both P < 0.001), and there was not a significant difference in percent change between the two methods, although there was a substantial absolute difference (similar to 2 kg) at baseline between the two methods. Although Bland-Altman plots indicate overall agreement between the percent thigh SM mass changes of DXA vs CT methods, the 3.4% error associated with DXA was greater than the thigh SM mass change from DXA. However, the CT measured change in thigh SM mass was greater than its error (0.6%). Conclusions: DXA overestimates baseline and after ST thigh SM mass, and may not be able to detect small changes in thigh SM mass with ST due to its higher error. Although DXA has certain advantages that warrant is used in epidemiologic and intervention studies, improvements to DXA are needed for the accurate assessment of small changes in thigh SM mass.