Exercise stimulates the release of irisin by muscle tissue, which might explain many of the beneficial effects of physical activity. Irisin increases the activity of genes associated with muscle growth and converts white adipose tissue to a darker, more thermogenic (calorie-burning) type of fat cell. It also improves blood sugar regulation by reducing insulin resistance. Irisin increases IGF-I, a powerful anabolic hormone, and decreases the activity of the myostatin gene, which limits muscle growth. It also increases energy expenditure, which reduces fat accumulation. Not all scientists agree. Irisin levels are high in obese animals and humans. The fat cells might secrete irisin in an effort to normalize fat metabolism. Irisin could be a marker of poor regulation of metabolism or it could be an important chemical that triggers many of the beneficial effects of exercise.
Source: www.Medscape.com, April 7, 2015