Similarly, Masson’s trichrome staining showed that the myocardial tissues of rats in the DM group exhibited a marked increase in collagen deposition in the interstitial and perivascular areas when compared with those of rats in the NC group, which was clearly mitigated in all regions of the myocardial tissues in T2DM rats following swimming and r-irisin interventions (Fig 4A, 4C and 4D). This evidence concerns the gene FNDC5 and type 2 diabetes mellitus.