Editorial: Advancing muscle health: from technical and clinical research to practice

The manuscripts that comprise the Research Topic issue, Advancing Muscle Health: From Technical and Clinical Research to Practice, highlight 'muscle health' as a multidimensional construct rather than a single outcome measure. (1) Skeletal muscle is a multifunctional organ involved in force production, metabolic regulation, endocrine signaling, postural control, and immune modulation.(2,3) Declines in muscle health contribute to sarcopenia, frailty, falls, metabolic dysfunction, and loss of independence, imposing substantial personal and societal burdens. Recent literature reveals substantial conceptual overlap in core domains of muscle health, yet wide variation in recommended tools, measurement cutoff or threshold values, and the interpretation of outcome measures. (4) This heterogeneity limits reproducibility, comparability across studies, and routine clinical adoption.Various groups have addressed the need for a common typology and framework for muscle health. 7) By linking body systems/structures to individual participation, the framework provides rehabilitation professionals (e.g., physical therapists, physiatrists, occupational therapists) with a language and structure that directly informs activities of daily living (ADLs) and functional independence. The collective research within this field strengthens this call to action. The purpose of this editorial is to move beyond individual models through synthesizing their alignments and distinctions, then translating the integrated conceptual foundation into practical implementation steps for rehabilitation practice. This implementation roadmap emphasizes feasibility, standardization, and measurable impact on functioning.Terms that characterize skeletal muscle, such as muscle health or muscle quality, are inherently pluralistic constructs that cannot be reduced to any single physiological and/or clinical framework. Skeletal muscle exerts wide-system effects, and its operational definition varies depending on the domain of interest (e.g., force production, metabolism, thermoregulation, or myokine signaling). (2,8) No single endpoint measure serves all domains equally well, and the domain(s) of interest logically determines which questions are viable, which tools are appropriate, and what constitutes a meaningful outcome. This domain-based perspective untethers muscle health assessment from lean body mass-driven approaches alone and clarifies the distinction between measurement methods and targeted physiologic domains.Building on this foundation, Boncella and colleagues proposed a framework for muscle health that was derived from accepted definitions of physical health and operationalized using components from the ICF model. The ICF has been broadly adopted by physical rehabilitation practitioners and investigators. Consequently, this approach does not directly address myokine signaling, thermoregulation, or metabolic homeostasis as primary endpoints. Rather, it proposes formal components to guide the selection of outcomes that are well-suited for rehabilitation while also incorporating outcomes with utility across domains:This multidimensional approach provides a more complete picture than any singular outcome measure. Outcomes associated with these components map onto the ICF model inclusive of body systems/structures, activities, and participation, enabling clinicians to proactively and systematically assess muscle health in the context of patient-centered care. This ICF orientation is particularly advantageous for rehabilitation professionals, as it prioritizes how muscle changes translate into mobility, balance, falls risk, and participation restrictions, while still allowing for integration of clinically relevant environmental and personal factors. However, it should be noted that domain pluralism (the acknowledgement that distinct scientific disciplines and health professions approach muscle health through different theoretical lenses) is not without its challenges. The boundaries between physiological domains are heuristically useful but biologically fraught: myokine signaling shapes glucose metabolism, which modulates force production capacity, which in turn governs activity levels and myokine expression.These interdependencies suggest that the domains are not fully separable, but rather constitutive of one another. Moreover, while disciplinary pluralism has very practical advantages for researchers, it risks posing operational barriers in clinical and public health contexts where shared constructs, common staging criteria, and cross-disciplinary communication are practical necessities. Subsequently, our collective task includes identifying frameworks that incorporate outcome measures that retain meaning across domains without collapsing their distinctions. While the three components of body and tissue composition, muscle performance, and functional task performance are considered together within the muscle health framework, the individual outcome measures associated with each component (e.g., imaging indices, force production metrics, and functional performance tests) remain available as modular tools that other disciplines may adopt within their own theoretical frameworks and apply toward different interpretive purposes.Nevertheless, persistent barriers remain even when differing frameworks align: lack of universal cutoffs for muscle composition estimates, force/power normalization approaches, method-dependent estimates of muscle mass, and underreporting of protocol details (e.g., device settings, patient positioning, and operator experience. Table 1 conveys these challenges by cataloguing modalities, technical/protocol factors, primary measures, illustrative cut-offs, and interpretation nuances across commonly used measurement tools. Even as conceptual frameworks for muscle health continue to evolve, a persistent barrier remains: not the absence of measures, but the lack of a shared structure within which those measures can be meaningfully compared and interpreted.Recent frameworks converge on the need for structured, multidimensional approaches to muscle health while offering complementary strengths that support feasible and appropriate clinical implementation in rehabilitation. Boncella et al. (2025) position their model as an aspect of physical health using the ICF as an organizing framework with three core, interrelated components (body and tissue composition, muscle performance, and functional task performance) that explicitly link biological impairments to activity limitations and participation restrictions. (4) In contrast, Heymsfield et al. (2023) propose a hierarchical model grounded in the principle that "outcomes follow function follow form" (the OFF rule). (6) In this framework, muscle form (mass, shape, composition) underpins function (strength, power, endurance, metabolic capacity), which in turn drives clinical outcomes (mobility, falls risk, independence, survival). The model draws from existing sarcopenia, malnutrition, and cachexia guidelines, advocating form and function as equivalent "gateway" nodes for screening and intervention while emphasizing that functional measures typically show stronger associations with patient-relevant outcomes. These two models align strongly: both endorse multidimensional assessment over single metrics and recognize the directional hierarchy from tissue-level properties to functional performance to participation. Integration of the ICF adds specific contextual factors (personal and environmental) and a standardized language for interdisciplinary teams, while the OFF model provides a clear pathophysiological rationale for prioritizing functional outcomes in guideline development and clinical decision-making. 5) This approach complements all prior models by addressing modifiable external drivers that influence progression along the continuum and within the form-function-outcome pathway.Important points of differences and alignment exist among these frameworks for rehabilitation practice include:• Scope of focus: The six-stage muscle health continuum and OFF model lean toward a medical/biological model with etiological subtypes and staging, while the ICF-informed muscle health perspective centers rehabilitation-relevant functioning and disability.• Prevention vs. treatment: The six-stage muscle health continuum explicitly supports proactive intervention in at-risk or subclinical individuals; the OFF model helps justify why early functional training yields outsized outcome benefits, but all of the frameworks are dependent on clear outcome measures, cutoff values, and standardized interpretation to have clinical relevance.• Aggregate measurement: All frameworks acknowledge that form (e.g., muscle mass estimates or ultrasound thickness) is foundational but insufficient alone. While real-world performance outcomes (e.g., mobility status or gait speed) provide valuable intervention targets, functional limitations cannot be explicitly attributed to muscle dysfunction without data from body or tissue composition estimates and standardized muscle performance measures.Together, these frameworks form a complementary ecosystem: the hierarchical OFF model ( 6) supplies pathophysiological logic, the ICF-informed muscle health framework (4) provides physical rehabilitation structure and typology, the six-stage muscle health continuum (9) adds temporal staging and prevention, and emerging perspectives concerning personalized interventions (5) further address modifiable factors. An appropriate synthesis of these perspectives may prove to resolve some limitations to implementation by moving from isolated domain assessment to an integrated, dynamic, person-centered approach suitable for diverse rehabilitation settings. Nonetheless, advancing muscle health frameworks is necessary but not sufficient. Realizing the clinical and research utility of muscle health assessment requires resolving the persistent variability in measurement protocols and data interpretation that currently limit cross-study comparability (Table 1).There has been a recent call to advance the implementation of muscle health in rehabilitation settings through the refinement of assessment guidelines (4). The following provides a roadmap to help transition from conceptual frameworks into actionable practice:Step 1: Formalize a Process to Standardize Protocols, Reporting, and Data Integration The gap between evidence generation and clinical adoption has been estimated to exceed a decade based on multiple independent analyses (10,11), underscoring the need for deliberate, structured mechanisms to accelerate the translation of muscle health research into standardized practice. With this, a layered consensus process is recommended to advance the field: Delphi rounds for discrete elements (e.g., grip strength protocol, ultrasound parameters and positioning) (12)(13)(14) and the RAND/UCLA Appropriateness Method for more complex decisions (15). Additionally, the use of standardized reporting templates would serve to capture key technical variables (as shown in Table 1) to improve reproducibility and foster multidisciplinary communication. Consensus on the specific measures appropriate to both clinical and research settings is an important next step for the field.Step 2: Adopt a Tiered Assessment Approach Begin with a core minimum battery of feasible, high-yield measures spanning each of the three ICF-informed muscle health components: body and tissue composition, muscle performance, and functional task performance. First-tier measures should be broadly accessible, time-efficient, and sufficient to identify individuals at risk or in subclinical stages of muscle health decline to inform whether further assessment is warranted. When clinical context, available resources, or monitoring needs require greater precision, second-tier assessment using advanced imaging, laboratory measures, or instrumented performance testing can be utilized accordingly. This tiered structure is a diagnostic approach that matches assessment complexity to clinical need, supports the proactive identification of at-risk individuals, and may preserve comparability across practice settings. In addition, more resource-intensive modalities may serve a distinct and necessary function in research settings: generating normative data, validating cut-off values, and garnering mechanistic insights.Step 3: Systematically Address Unresolved Methodological Variation Table 1 highlights persistent sources of heterogeneity that must be addressed for reliable implementation. Key areas of unresolved variation include: 18) Also, determining how to interpret and appropriately weight estimates of muscle mass and muscle composition relative to physical performance and health outcomes remains an unresolved challenge in the field. Regarding physical performance measures, the clinical meaning of a given value often depends on normalization approaches, the presence of comorbidities, and the influence of non-muscle organ systems on functional status. ( 19)The papers in the Advancing Muscle Health: From Technical and Clinical Research to Practice Research Topic issue represent significant technical and clinical advances concerning the assessment of skeletal muscle. However, the collective works in the journal issue also illustrate how research progress is increasingly constrained by methodological heterogeneity. The growing interest and recently published muscle health frameworks highlights a critical inflection point for the field. (4,5,20,21) The next critical phase is formalized consensus development regarding the implementation of muscle health assessments. International organizations, funding bodies, and professional societies will need to support a formal consensus process focused on:1. Minimum viable muscle health assessment core measures for both clinical and research settings. 2. Standardized outcome measure protocols and training curricula. 3. Clinically meaningful change thresholds and common approaches to normalizing data. 4. Potential integration of medical/biological frameworks for muscle health with the ICFinformed assessment approach in physical rehabilitation settings. 5. Pathways for embedding muscle health metrics into patient-centered care models to build cohesive data sets and support proactive interventions.Rehabilitation professionals are uniquely qualified to play a leading role in this effort. By adopting a synthesized framework for muscle health that is inclusive of the ICF domains and typology, we can move muscle health assessment from conceptual models to a routine clinical assessment approach, ultimately preserving function, reducing disability, and enhancing quality of life across the lifespan.