Myokines

Myokines are signaling molecules produced and released by skeletal muscle cells that can act locally or communicate with other tissues. The concept developed from evidence that contracting muscle behaves as a secretory organ, producing cytokines and other peptides whose actions may be autocrine, paracrine, or endocrine .^1,2

Interleukin-6 was an early and influential example because its concentration can rise markedly during prolonged muscle contraction. Other proposed myokines include proteins involved in muscle growth, metabolism, inflammation, vascular biology, and communication with adipose tissue, liver, bone, and the nervous system. Their release can depend on exercise type, intensity, duration, energy status, and the physiological state of the muscle .^1,2

The label myokine does not mean that a molecule is produced only by muscle or that every change in its blood concentration during exercise came from muscle. Many proposed myokines are also made in other tissues, and some act mainly near their site of release rather than as circulating hormones. The term is therefore defined by muscle production and signaling function, not simply by being detectable in blood after exercise .¹