Combination of DXA and BIS body composition measurements is highly correlated with physical function-an approach to...

Fluid volume estimates may help predict functional status and thereby improve sarcopenia diagnosis.

Bioimpedance-derived fluid volume, combined with DXA, improves identification of jump power over traditional measures.

DXA-measured lean mass should be corrected for fluid distribution in older populations; this may be a surrogate of muscle quality.

Sarcopenia, the age-related loss of muscle mass and function, negatively impacts functional status, quality of life, and mortality. We aimed to determine if bioimpedance spectroscopy (BIS)-derived estimates of body water compartments can be used in conjunction with dual-energy X-ray absorptiometry (DXA) measures to aid in the prediction of functional status and thereby, ultimately, improve the diagnosis of sarcopenia.

Participants (≥ 70 years) had physical and muscle function tests, DXA, and BIS performed. Using a BMI correction method, intracellular water (ICWc), extracellular water (ECWc), and ECWc to ICWc (E/Ic) ratio was estimated from standard BIS measures. Jump power was assessed using jump mechanography.

The traditional measure used to diagnose sarcopenia, DXA-derived appendicular lean mass (ALM) corrected for height (ALM/ht2), was the least predictive measure explaining jump power variability (r2 = 0.31, p < 0.0001). The best measure for explaining jump power was a novel variable combining DXA ALM and BIS-derived E/Ic ratio (ALM/(E/Ic); r2 = 0.70, p < 0.0001). ALM/(E/Ic) and ICWc had the highest correlation with jump power and grip strength, specifically jump power (r = 0.84 and r = 0.80, respectively; p < 0.0001).

The creation of a novel variable (ALM/(E/Ic)) improved the ability of DXA to predict jump power in an older population. ALM/(E/Ic) substantially outperformed traditional lean mass measures of sarcopenia and could well be an improved diagnostic approach to predict functional status. DXA-measured ALM should be corrected for fluid distribution, i.e., ALM/(E/Ic); this correction may be considered a surrogate of muscle quality.