The role of exercise-induced myokines in muscle homeostasis and the defense against chronic diseases.

Chronic inflammation is involved in the pathogenesis of insulin resistance, atherosclerosis, neurodegeneration, and tumour growth. Regular exercise offers protection against type 2 diabetes, cardiovascular diseases, colon cancer, breast cancer, and dementia. Evidence suggests that the protective effect of exercise may to some extent be ascribed to the antiinflammatory effect of regular exercise. Here we suggest that exercise may exert its anti-inflammatory effect via a reduction in visceral fat mass and/or by induction of an anti-inflammatory environment with each bout of exercise. According to our theory, such effects may in part be mediated via muscle-derived peptides, so-called "myokines". Contracting skeletal muscles release myokines with endocrine effects, mediating direct anti-inflammatory effects, and/or specific effects on visceral fat. Other myokines work locally within the muscle and exert their effects on signalling pathways involved in fat oxidation and glucose uptake. By mediating anti-inflammatory effects in the muscle itself, myokines may also counteract TNF-driven insulin resistance. In conclusion, exercise-induced myokines appear to be involved in mediating both systemic as well as local anti-inflammatory effects.