Echo intensity (EI) has gained popularity as a method for quantifying ultrasound-derived muscle quality in older adults, which may reflect non-contractile tissue accumulation. However, since water is hypo-echoic, previous authors have suggested that alterations in hydration status and/or intracellular water content (ICW) may influence EI. PURPOSE: To assess the influence of hydration status and segmental ICW on EI in older men. METHODS: Twenty normal weight, healthy, older men (mean ± SD age: 69.5 ± 2.0 yrs; body mass index: 23.6 ± 1.2 kg/m2) refrained from vigorous exercise for 48 hours and fasted for a minimum of eight hours prior to visiting the laboratory on one occasion. A clinical handheld refractometer was used to assess hydration status via urine specific gravity (USG). Panoramic brightness mode ultrasound imaging was used to determine anatomical cross-sectional area (CSA) and EI. Following a 20-minute lying rest period, one scan of each superficial quadricep muscle (vastus lateralis, rectus femoris, vastus medialis) was taken of the right thigh at 50% femur length with the leg propped and supported at 50 degrees of flexion. Cross-sectional area was summed and EI was averaged across all three muscles. Segmental bioelectrical impedance spectroscopy was used to measure ICW and extracellular water content (ECW) of the right thigh. Total body water (TBW) of the segment was determined from the sum of ICW and ECW. The ICW values were normalized to TBW prior to analyses. Pearson’s product-moment correlation coefficients were used to assess the association between EI and USG and ICW/TBW. Given previous authors have suggested ICW reflects the amount of contractile tissue, a partial correlation was used to assess the association between EI and ICW/TBW while controlling for CSA. RESULTS: Echo intensity (96.9 ± 12.6 a.u.) was not associated with USG (1.016 ± 0.01) (P = 0.865). Poorer EI (higher value) was negatively associated (r = -0.527, P = 0.02) with lower ICW/TBW (0.50 ± 0.04) prior to and after accounting for CSA (29.8 ± 4.7 cm2) (r = -0.518, P = 0.02). CONCLUSIONS: Hydration status did not influence EI in a group of largely euhydrated (70%) older adults. Thigh specific segmental ICW content influences EI values in older adults. Future studies are needed to determine how ICW content influences age-related differences in EI.
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