Usefulness of muscle echo intensity for evaluating functional performance in the older population: A scoping review

Muscle echo intensity, as measured by ultrasonography, could be used as a new marker of functional performance in older populations. This scoping review aimed to present evidence on the utility of muscle echo intensity as determined by ultrasonography for assessing functional performance in older adults. The eligibility criterion included observational studies that investigated the associations between muscle echo intensity and functional performance in older adults. Terms, such as "echo intensity" and "older adults", were searched for in databases, such as PubMed, Web of Science, the Cochrane database of systematic reviews, and the Cumulative Index of Nursing and Allied Health Literature, in April 2021. Two independent reviewers screened and extracted the data; 46 papers, of which almost one-third were Japanese, were subsequently identified for inclusion. The representative functional performances included in this review were muscle strength, gait speed, sit-to-stand test results, and timed up-and-go test results. Poor to moderate associations were found between muscle echo intensity and functional performance; however, heterogeneities were observed in the characteristics of study participants. Moreover, the accurate effect size and causal inferences between muscle echo intensity and functional performance remained unclear. Further longitudinal studies are needed to determine these causal inferences.