Segmental DEXA scans used to measure muscle mass in different body parts are not precise enough to consistently detect small increases in muscle size between people doing different exercise programs.
Mechanism
Synthesis from 1 study
DEXA scans measure big chunks of the body and can't tell the difference between muscle growing and water moving around. Since muscle gains from exercise are tiny, and water levels change all the time, the scan often can't tell if muscle actually grew or if it was just fluid.
Most probable mechanism
DEXA scans measure total lean mass in large body sections, but they can't tell the difference between actual muscle growth and small changes in water or other soft tissues nearby. Because muscle gains from training are tiny compared to these natural fluid shifts, the scan gets confused and can't reliably show if muscle really grew or if it was just water moving around.
Segmental DEXA scans measure total lean tissue mass within large anatomical regions, such as limbs or trunk, without distinguishing between muscle, connective tissue, blood volume, or extracellular fluid.
Small increases in muscle mass from training are on the same order of magnitude as natural fluctuations in extracellular fluid volume caused by hydration, sodium balance, or inflammation.
The spatial resolution of DEXA is insufficient to isolate muscle-specific changes within a segment, causing signal noise from non-muscle tissues to mask small hypertrophic changes.
Evidence from Studies
Supporting (0)
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Contradicting (1)
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Detection of small changes in body composition by dual-energy x-ray absorptiometry.
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