What Is “Muscle Health”? A Systematic Review and Conceptual Framework

Background: Muscle health is an emerging concept, increasingly cited in studies associated with physical performance and functional independence. However, the term lacks a clear operational or conceptual definition and often serves as a general descriptor of any muscle-related outcome. Clinical communication and research designs would benefit from a sound conceptual model of muscle health grounded in an established framework concerning physical health and muscle function. Methods: Thus, our proposed model is informed by a systematic literature review and synthesis regarding the multi-factorial measurement approaches used to characterize skeletal muscle. Three investigators screened 333 papers with search criteria for clinical and randomized controlled trials and "muscle health". Results: Of the 68 papers that met inclusion criteria, 31 studies provided an operational definition of "muscle health", while 37 inferred measurements without a clear definition. The identified measurements spanned four primary categories, with body composition/muscle mass being the most common (92.7%), followed by muscle performance (76.5%), physical function (61.8%), and tissue composition (30.9%). Most studies included more than one muscle health metric (94.1%). Common assessment methods included DXA (41.2%), grip strength (63.2%), and gait speed (26.5%). Conclusions: Using the framework of the International Classification of Functioning, Disability and Health, measurement categories identified aligned with muscle health components of muscle morphology/morphometry (e.g., muscle mass and composition), functional status (performance-based tasks), and physical capacity (objective maximal or submaximal measures of muscle performance). Consistently applying these measurement domains could aid the assessment of muscle health and facilitate further work to standardize specific approaches to testing and data interpretation across settings.