Exploring the associations between skeletal muscle echogenicity and physical function in aging adults: A systematic review with meta-analyses

Abstract

BackgroundAssessment and quantification of skeletal muscle within the aging population is vital for diagnosis, treatment, and injury/disease prevention. The clinical availability of assessing muscle quality through diagnostic ultrasound presents an opportunity to be utilized as a screening tool for function-limiting diseases. However, relationships between muscle echogenicity and clinical functional assessments require authoritative analysis. Thus, we aimed to 1) synthesize the literature to assess the relationships between skeletal muscle echogenicity and physical function in older (≥60 years) adults, 2) perform pooled analyses of relationships between skeletal muscle echogenicity and physical function, and 3) perform sub-analyses to determine between-muscle relationships.MethodsCINAHL, Embase, MEDLINE, PubMed, and Web of Science databases were systematically searched to identify articles relating skeletal muscle echogenicity to physical function in older adults. Meta-analyses with and without sub-analysis for individual muscles were performed utilizing Fisher’s Z transformation for the most common measures of physical function. Fisher’s Z was back-transformed to Pearson’srfor interpretation.ResultsFifty-one articles (N=5095, female=∼2759, male=∼2301, 72.5±5.8 years [one study did not provide sex descriptors]) were extracted for review, with previously unpublished data obtained from the authors of 12 studies. The rectus femoris (n=32) and isometric knee extension strength (n=22) were the most accessed muscle and physical qualities, respectively. The relationship between quadriceps echogenicity and knee extensor strength was moderate (n=2924,r=-0.36 [95%CI: −0.38 to −0.32],p<0.001), with all other meta-analyses (grip strength, walking speed, sit- to-stand, timed up-and-go) resulting in slightly weaker correlations (r=−0.34 to −0.23, allp<0.001). Sub-analyses determined minimal differences in predictive ability between muscle groups, although combining muscles (e.g., rectus femoris+vastus lateralis) often resulted in stronger correlations with maximal strength.ConclusionsWhile correlations were modest, the affordable, portable, and noninvasive ultrasonic assessment of muscle quality was a consistent predictor of physical function in older adults. Minimal between-muscle differences suggest that echogenicity estimates of muscle quality are systemic. Therefore, practitioners may be able to scan a single muscle to assess full-body skeletal muscle quality/composition, while researchers should consider combining multiple muscles to strengthen the model.RegistrationThe original protocol was prospectively registered at the National Institute of Health Research PROSPERO (CRD42020201841).HighlightsRelationships between skeletal muscle echogenicity and physical function were small to moderate, but highly consistent.Sub-analyses determined minimal between-muscle differences in predictive ability.Ultrasonic echogenicity should be considered part of early detection screens for sarcopenia and other diseases.Combining muscles tended to strengthen the model, although muscle quality appears systemic, allowing for a single scan to represent the total body.