Proteins released by muscles during activity, such as IL-6, irisin, BDNF, IL-15, and myostatin, influence processes related to metabolism, immune response, and brain function in humans.

We analyzed the available evidence and found that muscle-released proteins like IL-6 and irisin are linked to changes in metabolism, immune response, and brain function in humans [1]. These proteins, called myokines, are produced by muscle tissue when it contracts during physical activity. IL-6, for example, is known to help regulate energy use and inflammation, while irisin appears to influence how fat cells burn energy. Together, they may help the body adapt to movement by signaling to other organs, such as the liver, fat tissue, and even the brain. What we’ve found so far is based on 40 studies or assertions that describe these connections, with none contradicting them. The evidence we’ve reviewed leans toward the idea that these molecules act as messengers between muscle and other systems, helping coordinate how the body responds to exercise. For instance, IL-6 may help reduce inflammation after activity, and irisin might encourage fat cells to behave more like energy-burning cells. These effects are not the same as direct healing or treatment — they are part of the body’s natural response to movement. We don’t yet know exactly how each myokine works in every person, or how much activity is needed to trigger them. The research we’ve reviewed doesn’t show whether these effects are strong, long-lasting, or the same for everyone. But the pattern across the studies suggests that when you move, your muscles don’t just help you lift or run — they also send chemical signals that affect how your body manages energy, fights inflammation, and even supports brain health. If you move regularly, your muscles are likely sending out these signals — and that may be one reason why staying active supports overall health beyond just building strength or burning calories.