FNDC5 and obesity due to melanocortin 4 receptor deficiency: ,S32,S33 Mouse exposure to swimming or free wheel running, and human exposure to 10 weeks of aerobic training induced the secretion of irisin from skeletal muscle into blood, which has been demonstrated to increase energy expenditure by stimulating the ‘browning’ of white adipose tissue.S34,S35 In addition to the potential use of irisin as a therapeutic agent against obesity or type 2 diabetes, irisin also functions as a promyogenic factor.