Extended Abstract
1. Objectives
Overweight/obesity increases the risk of postmenopausal breast cancer [1]. The risk of breast cancer in obese postmenopausal women is associated with increased estrogens and reduced sex hormone-binding globulin levels [2]. Sex hormone-binding globulin may reduce the risk of this disease through the inhibition of estradiol effects [3]. Furthermore, insulin is directly associated with breast cancer risk in postmenopausal women and may be an intermediary between obesity and breast cancer [4]. 
Previous studies have suggested that physical activity particularly reduces the risk of postmenopausal breast cancer [5, 6]. Physical activity may reduce the risk of this disease through several mechanisms, including changes in endogenous estrogens, sex hormone-binding globulin, and insulin resistance [7]. Therefore, this study aimed to investigate the effect of aerobic training on some hormonal and metabolic factors associated with breast cancer, such as sex hormone-binding globulin and insulin in overweight postmenopausal women.    
2. Methods and Materials
In this quasi-experimental study, 24 overweight/obese sedentary postmenopausal women were randomly assigned to the experimental (n=14) and control (n=10) groups. The experimental group received an aerobic exercise program on the basis of 3 sessions/week for 10 weeks. The aerobic training consisted of 25-45 minutes of walking/running at an intensity of 65%-75% of Maximum Heart Rate (MHR). The aerobic exercise started with the intensity of 65% of MHR for 25 minutes and gradually progressed to 75% of MHR for 45 minutes by the end of the 10th week. The control group did not participate in any physical exercise training. Physiological and biochemical variables, including body weight, body fat percentage, maximal oxygen uptake (Vo2 max), sex hormone-binding globulin, insulin and glucose levels, and insulin resistance were assessed at the beginning and after the completion of the aerobic training program. Body weight and body fat percentage were assessed by a body composition analyzer (Omron, Finland).
Maximal oxygen uptake was determined using a submaximal aerobic test (Rockport Fitness Walking Test). The blood samples were collected after 10-12 hours fast at the baseline and 48 hours after the last training session. These samples were obtained to measure sex hormone-binding globulin, insulin and glucose levels. Sex hormone-binding globulin level was measured by Enzyme-Linked Immunosorbent Assay (ELISA) kit (ALPCO Diagnostic). Serum insulin was evaluated by immunoradiometric assay kit (IM3210; Immunotech, Czech Republic). Fasting blood glucose was assessed by glucose oxidase method kit (Pars Azmoon, Iran). Insulin resistance was calculated using the Homeostatic Model Assessment of Insulin Resistance (HOMA-IR). Independent Samples t-test was used to explore the difference in baseline characteristics between the two groups. The Analysis of Covariance (ANCOVA) was applied to compare changes between the experimental and control groups. The level of significance was set at P<0.05. 
3. Results
All of the studied subjects were either overweight or obese. They had a mean Body Mass Index (BMI) of 32.01 kg/m2, a mean body fat percentage of 43.5%, and a mean age of 55.44 years. The mean vo2 max of the studied subjects was also 20.81 mL/kg/min, indicating poor aerobic fitness. The baseline characteristics of the experimental and control groups were compared. The obtained baseline results suggested no statistically significant differences in age, weight, BMI, body fat percentage, and vo2 max between the two groups (P>0.05). The ANCOVA results revealed no significant differences in sex hormone-binding globulin (P=0.37), glucose (P=0.22), insulin (P=0.39), insulin resistance (P=0.9), and body fat percentage (P=0.57) between the experimental and control groups after 10 weeks of aerobic training; however, a significant difference was found in vo2 max (P=0.03) between the two groups.
4. Conclusion 
The achieved results suggested that 10 weeks of moderate-intensity aerobic training has no effect on some hormonal and metabolic factors associated with breast cancer, such as sex hormone-binding globulin, insulin, insulin resistance, and body fat percentage in overweight postmenopausal women; however, it improved their cardiovascular fitness. It appears that the levels of sex hormone-binding globulin and insulin make no favorable changes in response to exercise training, that does not reduce BMI. Moreover, several factors such as intensity, duration, the type and volume of exercise training may affect the exercise-induced changes in sex hormone-binding globulin and insulin levels. In the present study, the intensity or duration of training may have not been adequate to make changes in sex hormone-binding globulin and insulin levels. Therefore, further studies are recommended to evaluate the effectiveness of training programs with different intensities and durations.
Ethical Considerations
Compliance with ethical guidelines
This study was approved by Islamic Azad University of Karaj, and all subjects completed the consent form before participating in the research.
Funding
This study is extracted from the MSc. thesis of the first author, in Faculty of Physical Education and Sport Science, Islamic Azad University, Karaj Branch.
Authors contributions
All authors contributed in designing and preparing this study.
Conflict of interest
The authors declared no conflict of interests.