en تخصصي Special پژوهشي Research Objective: High intensity interval training (HIIT) and continues aerobic training have cardio-protective effects in diabetic rats. The aim of this study was to compare the effect of HIIT and continues aerobic training (CAT) on MIR29A and collagen I gene expression in heart of diabetic male rats.<br> Materials and Methods: In this randomized controlled clinical trial, 18 male diabetic rats were studied. They were divided into 3 groups as HIIT, CAT and control group. Exercise protocol was performed 5 days/week for 5 weeks. The MIR29A and collagen I synthesis were compared between the groups.<br> Results: Findings showed MIR29A expression is statistically higher in HIIT and CAT group than control group (P-value<0.001) and (P-value:0.053). Also MIR29A expression is significantly higher in HIIT group compared to CAT group (P-value:0.034). Collagen I expression was significantly lower in HIIT and CAT group compared to control group (P-value<0.001) and (P-value:0.001). Collagen I expression was lower in HIIT group compared to CAT group (P-value:0.027).<br> Discussion: The results of this study demonstrated that, HIIT increases MIR29A expression which is along with reduction in collagen I synthesis in cardiac muscles increases the risk of myocardial fibrosis in diabetic rats.<br> <br> &nbsp; High intensity interval training, Continues aerobic training, Diabetic rats, MIR29A, Collagen I 183 190 http://ijdo.ssu.ac.ir/browse.php?a_code=A-10-30-157&slc_lang=en&sid=1 Mania Roozbayani Yes Coach of Exercise Physiology, Department of Exercise Physiology, Boroujerd, Islamic Azad University, Boroujerd, Iran. Maghsoud Peeri No Professor of Exercise Physiology, Department of Exercise Physiology, Central Tehran Branch, Islamic Azad University, Tehran, Iran. Hamid Agha-Alinejad No Associate Professor of Exercise Physiology, Faculty of Humanities, Tarbiat Modares University, Tehran, Iran. Mohammad Ali Azarbayjani No Professor of Exercise Physiology, Department of Exercise Physiology, Central Tehran Branch, Islamic Azad University, Tehran, Iran.