Irisin/FNDC5 Gene Expression in Fast-Twitch Extensor Muscles of the Forelimb and Slow-Twitch Soleus Muscles of Male Wistar Rats Affected by Resistance, Endurance, and Concurrent Training: Comparison between Different Types of Training

Exercise can exert its beneficial effects through specific mediators. One of the organs that is most affected during exercise is the skeletal muscles. These muscles release various myokines, of which irisin is one of the major ones that has been recently identified. However, the way the irisin gene, FNDC5, responds to different exercise training has not yet been fully elucidated. This foundational research aimed to investigate the effects of three different types of exercise on FNDC5 gene expression in the muscles of rats. 40 healthy male Wistar rats were divided into four ten groups of control, resistance training, endurance training and concurrent training. Each group did their own specific exercises for 8 weeks, except for the control group, which did not have any specific activities. Finally, fast-twitch extensor muscles of the fingers and slow-twitch soleus muscles were tested to measure FNDC5 gene expression. The analysis results showed that FNDC5 gene was expressed in all groups with a significant difference (P <0.001). The relative expression of FNDC5 gene was significantly increased in all training groups compared to the control group (P <0.001). In addition, comparing exercise groups together, combined exercises showed the greatest effect and endurance exercise showed the least effect. In intra-group comparison, the expression of FNDC5 gene in forelimb and hindlimb muscles was not significantly different (P > 0.05). All trainings could increase the expression of FNDC5 gene compared to the control group, but combined, resistance and endurance exercises had the greatest effect, respectively.