Background & Aims: Myonectin is one of the newly known myokines that is secreted from skeletal muscle and is related to the metabolic status of the body, so that in starvation conditions, myonectin levels decrease and increase after receiving calories. Various studies have shown that there is a relationship between myonectin and metabolic variables such as insulin resistance (2). In previous studies, it has been reported that in sedentary people, myonectin levels decrease and exercise increases their myonectin levels. On the other hand, unlike obesity, exercise can increase myonectin (5). Exercise dramatically increases circulating expression and levels of myonectin to increase the uptake of fatty acids into cells (11). Given that myonectin has been discovered in recent years, there are still many ambiguities about this hormone and its function in the body and its changes in various conditions such as exercise and physical activity. Due to this issue, the aim of the present study was to investigate the effect of 8 weeks of high intensity interval swimming training on serum levels of myonectin and insulin resistance in postmenopausal women. Methods: 24 subjects (age 55. 73 2 2. 66 years, body mass index 26. 72 ±,2. 33 kg / m2) were selected as the sample size. Inclusion criteria include: having swim skills, lack of regular exercise in the last 6 months, no history of cardiovascular disease, blood, liver, respiratory, kidney, hormonal disorders, sleep disorders, smoking and no surgery Over the past year, there has been no history of taking specific medications and a ban on physical activity by the treating physician. Exclusion criteria also included absent for more than 2 sessions, illness of the subjects and dissatisfaction of the subject with continuing work and lack of cooperation. All stages of the research were informed to the subjects according to the 2013 Helsinki Declaration, and then the subjects completed the informed consent form and the necessary explanations were given regarding the confidentiality of their information. Subjects were randomly divided into control and experimental groups. Then, the necessary explanations were provided to each group about nutrition and the amount of sports activities. After that, the experimental group completed a questionnaire of readiness to participate in sports activities and were examined by a cardiologist to confirm their health for participating in sports activities. One week before the start of the training program, the subjects were introduced to how to do the research and the training program. Height and weight were measured. Metabolic indices of glucose, insulin at rest and blood sampling were measured in 12-10 hours of fasting (8 to 9 am) in two stages 48 hours before exercise and 72 hours after exercise. Subjects were asked to avoid doping exercise for 48 hours prior to sampling. Also, sampling was performed in the post-test at a specific time and similar to the pre-test. The training program included 8 weeks of high intensity interval swimming training that were performed in three sessions per week. These exercises were performed under the supervision of a swimming instructor and in the presence of lifeguards in the pool. Each swimming exercise session consisted of the following steps: A: Warm-up phase: The warm-up session included stretching and gentle swimming in the pool, which was performed for ten minutes. B: Specific training phase: This phase consisted of 30-second repetitions of fast swimming, with 2 minutes of active rest between repetitions. These repetitions were performed in weeks 1 and 2 as 6 repetitions, in weeks 3, 4 and 5 as 8 repetitions and in weeks 6, 7 and 8 as 10 repetitions. C) Cooling stage: At the end of each training session, stretching movements and gentle swimming were performed for ten minutes to cool down and return to the original state (16). During the study period, the subjects in the control group did not have any regular exercise. Participation in the research process was completely voluntary and subjects were allowed to leave the research at any time. Finally, the results of 12 people from each group were extracted. Data were analyzed using paired and independent t-test at a significance level of P 05 0. 05. Results: 8 weeks of high intensity interval swimming training increased myonectin, decreased insulin and insulin resistance (p ≤,0. 05). But it had no significant effect on glucose content. No serious illness or injury was reported during the study period and all stages of testing and assessment were performed in full. The results of the present study showed that eight weeks of high intensity interval swimming training significantly increased fasting mayonnaise (p ≤,0. 01). It was also observed that the amount of glucose, insulin and fasting insulin resistance decreased significantly after eight weeks of high intensity interval swimming training (p ≤,0. 01). Conclusion: Increased myonectin levels during exercise can cause AMPK phosphorylation, which leads to increased GLUT4 utilization and increased glucose uptake and stimulation of free fatty acid oxidation (22). Therefore, increasing the secretion of myonectin as a result of muscle contraction during exercise can activate the energy production pathways required during contraction. In other words, myonectin plays a similar role to insulin. However, this increase in myonectin levels is delayed by 2 hours after glucose or lipid intake, in other words, myonectin stimulates the uptake of glucose or fatty acids with a delay (22). previous research has shown that exercise is an effective tool to improve the metabolic status of the body, especially in obese people, but the mechanism of this issue has always been in a state of ambiguity. In addition to aliquot alteration and its possible role in reducing insulin resistance, exercise is recognized as a very important factor in the uptake of blood glucose by muscles without the involvement of insulin, at which stage the mediating role of GLUT 4 is crucial. During exercise insulin receptors respond more appropriately to lower levels of insulin, which lowers blood sugar and ultimately prevents diabetes (27). It is consistent because it was observed that after 8 weeks of high intensity interval swimming training, insulin and glucose levels decreased. It seems that high intensity interval swimming training can be used to increase myonectin and also improve insulin resistance in overweight postmenopausal women. The results of the present study showed that in response to high intensity interval swimming training, an increase in myonectin was associated with a decrease in insulin resistance in overweight women. Further research is needed to elucidate the role of myonectin in improving insulin resistance.