# Decoding the Endocrine Code of Skeletal Muscle: Myokines, Exerkines, and Inter-Organ Crosstalk in Metabolic Health and Disease

## TL;DR

This review explores how skeletal muscle communicates with other organs through secreted factors, influencing metabolic health and disease.

## Contribution

The paper introduces the concept of an 'endocrine code' in muscle signaling and outlines translational opportunities for metabolic health.

## Key findings

- Muscle-derived signals operate through integrated patterns rather than isolated factors.
- EVs serve as a complex delivery system requiring rigorous validation.
- Translational strategies include targeting pathways like myostatin/activin and FGF21.

## Abstract

Skeletal muscle is increasingly recognized as a dynamic endocrine and paracrine organ that communicates with distal tissues through a diverse secretome of peptides, proteins, metabolites, and extracellular vesicles (EVs), collectively referred to as myokines and exerkines. Beyond cataloging individual factors, emerging evidence suggests that muscle-derived signals can convey information through an integrated, context-dependent “endocrine code”—a pattern defined by secretion kinetics, co-released signal combinations, delivery modalities, and target-tissue receptor landscapes. This review synthesizes current evidence on (i) conceptual and experimental criteria for defining bona fide myokines, (ii) mechanisms governing myokine expression, processing, and release across exercise modes and physiological states, and (iii) major muscle–organ axes that connect physical activity to systemic metabolic homeostasis, immune remodeling, tissue regeneration, and neurocognitive adaptation. We further discuss non-protein mediators such as lactate, succinate, and β-aminoisobutyric acid, and highlight EVs as a multiplexed delivery modality whose interpretation requires stringent isolation, contamination controls, and functional validation. Finally, we evaluate translational opportunities—including biomarker panels, therapeutic targeting of the myostatin/activin, fibroblast growth factor 21 (FGF21), and growth differentiation factor 15 (GDF15) pathways, and precision exercise prescriptions informed by multi-omics and artificial intelligence—while emphasizing analytical standardization, causal validation, and transparent reporting as prerequisites for clinical impact.