Inflammation-Insulin Resistance Crosstalk and the Central Role of Myokines.

Insulin resistance develops when skeletal muscle (SM), adipose tissue (AT), and the liver fail to respond adequately to insulin, a dysfunction closely intertwined with chronic low-grade inflammation. This combination leads to compensatory hyperinsulinemia, dysglycemia, and metabolic stress, driving major disorders such as type 2 diabetes, metabolic syndrome, metabolic dysfunction-associated steatotic liver disease (MASLD), and cardiovascular disease. Both adipokines and myokines are central modulators of this metabolic-inflammatory axis. In obesity, diabetes, MASLD, and thyroid dysfunction, alterations in myokines such as myostatin, irisin, fibroblast growth factor 21 (FGF-21), apelin, brain-derived neurotrophic factor (BDNF), interleukin-6 (IL-6), and interleukin-15 (IL-15) influence glucose uptake, lipid oxidation, mitochondrial function, and systemic inflammation. Exercise-induced myokines exert insulin-sensitizing and anti-inflammatory effects, whereas myostatin and tumor necrosis factor-alpha (TNF-α) promote metabolic impairment. These pathways reveal extensive crosstalk between SM and key metabolic organs-including the liver, pancreas, AT, intestine, heart, and thyroid gland. In metabolic disease, inflammation-driven changes in deiodinase activity and triiodothyronine (T3) availability further link muscle dysfunction with thyroid imbalance. The aim of this narrative review was to elucidate the complex interplay between myokines, adipokines, inflammation, and insulin resistance, and to clarify their clinical relevance in metabolic and thyroid disorders. Given this integrative role of SM, sarcopenia should be recognized as a clinical marker of metabolic or thyroid dysregulation, and preserving muscle mass through structured physical activity should be a core therapeutic target.