Fig. 1. Positive and negative regulators of skeletal muscle mass. Myokines are produced and secreted by skeletal muscle and act via autocrine, paracrine and endocrine mechanisms to regulate skeletal muscle mass and metabolism. IGF-1, insulin-like growth factor 1; IL, interleukin; BDNF, brain-derived neurotrophic factor; FGF-21, fibroblast growth factor 21; LIF, leukemia inhibitory factor.
