Agreement between rectus femoris muscle thickness by ultrasound and skeletal muscle mass by bio-electrical impedance analysis: a pilot study

Rationale: Sarcopenia is a major problem and is common in community-dwelling elderly. In daily practice, there is need for low cost and easily assessable measurement tools to assess depletion of skeletal muscle (SM) mass, for example as one of the indicators of sarcopenia. Bio-electrical impedance analysis (BIA) is often used to estimate body composition, whereas ultrasound measurement is an upcoming and promising tool, as it is quick, easy to use and inexpensive in comparison with other tools that assess SM mass. Ultrasound could assess site-specific loss of SM mass and determine myoesteatosis. Therefore, in this pilot study we aimed to assess agreement between muscle thickness of rectus femoris (RF) by ultrasound and SM mass by BIA in an older population.

Methods: Twenty-six older adults (mean± standard deviation (SD) age 64 ±5.0 y, 62% women) from the Hanze Health and Ageing Study were included. SM mass by BIA was estimated using the Janssen equation. Muscle thickness of RF was assessed by analyzing ultrasound images from the right leg. Two non-parametric tests were used for analysis. Correlation between ultrasound and BIA was assessed with Spearman Rho. Agreement was determined with Kendall’s coefficient of concordance (Kendall’s W). In both tests a score ≥ 0.7 was considered a strong correlation.

Results: Mean (±SD) RF thickness was 18.9 (±3.8) mm. Median SM mass (Interquartile range) was 23.5 (20.8-34.7) kg. Correlation between RF thickness and SM mass was moderately positive (Spearman r=0.611; P = 0.001), whereas Kendall’s W showed a strong agreement (W= 0.835; P=0.002).

Conclusion: Ultrasound measurement of RF showed an acceptable agreement with skeletal muscle mass assessed by BIA in our sample of older adults. Therefore, ultrasound could be a promising portable tool to estimate muscle size.