Background: The amount of muscle mass or muscle volume (MV) varies between individuals and is important for health, wellbeing, and performance. Imaging is a useful tool to monitor MV, magnetic resonance imaging (MRI) is considered gold standard. MRI are not always easily accessible, and the measurements are expensive, therefore ultrasonography
(US) has become a more accessible method for estimating MV.
Methods: A systematic literature review was conducted in the electronic databases PubMed, CINHAL and Web of Science with the purpose of collecting the current published equations to estimate MV with US and answering the following question: How well does US derived equations based on muscle thickness (MT) predict MV based on MRI?
Results: The literature search resulted in 363 citations. Twelve articles met the eligibility criteria and were included. Ten articles scored eight out of eleven on the QUADAS score and two scored nine out of eleven. 36 different prediction equations were identified. Correlations were good, r values ranged between 0.53-0.961 and the standard error of estimates (SEE) ranged between 6-25.6%. Eight studies did further analysis with a Bland-Altman plot and found no systematic errors. The overall strength and quality of the evidence was rated as “low quality” as defined by the GRADE system.
Conclusions: We conclude that the validity of US derived equations based on MT is specific to the populations from where it is developed. The agreement with MV based on MRI is moderate with SEE ranging between 6-12% in healthy populations. Suggestions for future research are to investigate if testing positions or increasing the number of measuring points could improve the validity for prediction equations.