Muscle Quality in Older Adults: A Scoping Review

Abstract

Objective: This scoping review aimed to map out currently available definitions and assessment methods of muscle quality in older adults.

Design: Scoping review.

Setting and participants: All available studies.

Methods: Four databases (PubMed, EMBASE, Web of Science, and Cochrane Library) were searched from inception to May 2022. Title, abstract, and full-text screening were undertaken by 2 reviewers independently. Observational and experimental studies were eligible for inclusion if there was a clear description of muscle quality assessment in individuals aged 60+ years.

Results: A total of 96 articles were included. Several definitions and assessment methods of muscle quality were identified and divided into 2 main domains: (1) functional domain, and (2) morphological domain. A total of 70% and 30% of the included studies assessed muscle quality in the functional and morphological domains, respectively. In the functional domain, most studies defined muscle quality as the ratio of knee extension strength by leg lean mass (45.9%). In the morphological domain, most studies defined muscle quality as the echo intensity of quadriceps femoris by ultrasound (50.0%).

Conclusions and implications: There is a substantial heterogeneity of definitions and assessment methods of muscle quality in older adults. Herein, we propose a standardized definition of muscle quality to include terminology, domain, and assessment methods (tests, tools, and body sites). Such standardization may help researchers, clinicians, and decision makers use muscle quality as a potential marker of "skeletal muscle health" in older adults.

Keywords: Aging; muscle mass; muscle strength; sarcopenia; skeletal muscle function deficit.