Recently a myokine named irisin has been discovered that effects on obesity, metabolism and glucose homeostasis through browning white adipose tissue and thermogenesis. However, the effects of type and intensity of exercises on it have remained unclear. The purpose of this study was to evaluate the effects of two acute eccentric and concentric exercises on serum irisin level and insulin resistance in obese sedentary women. Materials and Methods: The study was quasi-experimental. 15 female

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... ts with a body mass index above 30 kg/m 2 and mean age 24.86±2.87 years participated in the study. After measuring the maximal uptake oxygen of participants, they did two acute eccentric and concentric exercises using treadmill in a cross-over design within 10 days. After at least 8 hours-fasting, blood samples were collected before and immediately after each activity, to measure the levels of irisin, glucose and insulin. Data were analyzed using paired t-test and repeated measures ANOVA. In addition, Pearson correlation was used to examine the relationship between variables. Results: the irisin levels increased significantly after both types of exercises (p<0.05), that this increase in concentric activity was more than eccentric activity. Insulin resistance increased immediately after both exercises as well, that this increase in concentric exercise was statistically significant (p<0.05). Conclusion: However, both eccentric and concentric exercises had no effect on improving insulin resistance in obese women, but they can be considered as a good stimulus for the secretion of Irisin.