After taking into account adjustments of irisin concentration levels compared to the level of Homeostasis Model Assessment for Insulin Resistance (HOMA-IR), it was established that the highest values for the Irisin/HOMA-IR ratio were observed in international and local class athletes (who had low body fat mass content), whereas in people who engage in recreational physical activities (no more than 3 h per week) the ratio was approximately 50% lower. Here, FNDC5 is linked to Insulin resistance.