Ultrasound cut-off values for muscle thickness, cross-sectional area, and echo intensity in Caucasian adults: a narrative review

Background and Objectives: The aging process is accompanied by the loss of muscle mass. Ultrasound emerges as promising, although, ultrasound routine screening for low muscle mass is challenging due to the lack of reference values. This review presents a comprehensive overview of cut-off values for predicting and diagnosing low muscle mass and quality. Methods: We used PubMed, Web of Science, and Scopus databases to gather pertinent articles up until April 2024. The quality of the articles was screened with the Pretorius and Keating [2008] assessment questionnaire. Our aim was to identify articles that assessed cut-off values for skeletal muscle thickness, cross-sectional area (CSA), and echo intensity using ultrasound in Caucasian adults. Key Content and Findings: This review incorporates thirteen articles of high quality and four of moderate quality. Fifteen articles investigated cut-off values for muscle thickness of muscles in the arms, legs, and trunk. Four studies reported CSA cut-off values, and only two studies provided echo intensity cutoff values. It appears that the cut-off values are influenced by participant characteristics, the ultrasound measurement method, and the statistical method that is used to assess the cut-off value. Conclusions: This review represents an overview of muscle cut-off values for diagnosing conditions such as sarcopenia and low muscle mass. The most studied and useful cut-off values pertain to the muscle thickness measurements of the gastrocnemius, quadriceps, rectus abdominis, and tibialis anterior muscles.