Additionally, concurrent training significantly increased irisin levels in overweight or obese participants (SMD = 1.06, 95% CI [0.34–1.78], p = 0.00; I2 = 50.6%, heterogeneity p = 0.13) and in type 2 diabetes patients (SMD = 0.70, 95% CI [0.30–1.10], p = 0.00; I2 = 0%, heterogeneity p = 0.99). Here, FNDC5 is linked to type 2 diabetes mellitus.