Cardiovascular diseases are basically age-dependent diseases in men and women. The age-dependent progressive changes in anatomy and cardiovascular physiology, which are generally called ‘cardiovascular aging’, increase the probability of cardiovascular diseases during life by relating to cumulative exposure to traditional risk factors [1]. Several factors including stress, work environment, lifestyle, and occupation affect the development of cardiovascular diseases. Awareness of these factors can reduce the probable risk of these diseases [2], [3]. Cardiovascular risk factors include two categories of unalterable risk factors (such as age, gender, race, and family history) and alterable risk factors (such as high blood pressure, high blood glucose, physical activity and exercise, smoking, and blood lipids) [4]. Aging due to undesirable changes in the vessels including the stiffness of large elastic arteries (aortic and carotid arteries) and endothelial dysfunction are among the factors influencing these diseases.

The aging of vessels is caused by oxidative stress which decreases the bioavailability of nitric oxide (NO) and stimulates the developments in the extracellular matrix. The decrease of estrogen circulating in blood during menopause in women and the aging process are associated with vascular impairment. Regular aerobic exercise is the most evidence-based strategy to reduce the risk of cardiovascular diseases with the increase of age in men and women [5].

The vessels become stiff with aging and diseases (including high blood pressure, chronic kidney disease, diabetes, and atherosclerosis). The vessel stiffness increases due to structural changes such as elastin fragmentation, increased collagen levels, arterial calcification, glycation of both elastin and collagen, and mutual binding of collagen by advanced glycation end-products (AGE) [6], [7], [8], [9]. Quantitative angiographic studies have shown that exercise programs reduce the progress of coronary artery disease [9], [10], [11], [12]. Exercise may also change the resting lumen diameter in patients after coronary artery angioplasty. In fact, the re-stenosis level of the vessels was significantly lower in the patients (after angioplasty with balloon) randomly assigned to a 12-week intervention program consisting of daily exercise compared with that of patients in the control group [13]. Pulsed tension and shear stress are two main factors affecting the blood vessels. Pulsed tension is determined by arterial pressure fluctuations and is a force applied perpendicular to the longitudinal axis of the vessel. Shear stress is determined by blood flow and is a tensile force applied as a vector parallel to the longitudinal axis of the vessel. Scientific data suggest that the exercise-induced increase in endothelial shear stress has beneficial effects on vascular structure and reactivity. Exercise increases the intravascular blood flow and causes the vasodilation of epicardial coronary arteries which largely depends on endothelium integrity [13], [14], [15], [16]. Low shear stress is associated with increased wall thickness [17], [18], [19] and the acceleration of lumen clotting in the coronary arteries of patients with moderate disease severity. There is a continuous inverse relationship between shear stress and lumen stenosis [20]. While a low shear stress is associated with atherogenesis and disease progression, the regions with moderate to high shear stress are relatively immune to limb thickening as long as the blood flow remains unidirectional and axial [19].

The incidence levels of some chronic diseases are different in men and women. In western countries, women are less likely to have cardiovascular diseases than men and the premature mortality of men from these diseases is about 5.5 times higher than that of women. Although cardiovascular diseases are considered the most common cause of mortality and disability in women, the manifestations of these diseases occur 10 years later in women than in men [21]. In the study of Smeltzer et al., the prevalence of cardiovascular diseases was more in men. However, the current statistics indicate that women are more affected by these diseases than men [22]. A group of researchers showed that more than one and a half million women in the United States die from cardiovascular diseases each year [23]. The American Heart Association reported that acute myocardial infarction mortality was 5% more in women than in men [24]. In a research in Iran, it was reported that women are at greater risk of cardiovascular diseases due to less physical activity, multiple pregnancies, cultural, social, and economic status, level of education, dietary habits, and hormonal changes following aging and genetic differences [25]. In an investigation of cardiovascular risk factors, some researchers considered age, gender, and race in population levels as effective factors with different impacts over time [26]. Loss of estrogen likely increases the inflammatory processes associated with injury and microvascular inflammation over the course of menopause [27]. There is a gender difference at the cellular level due to the combined genetic effects of sex chromosomes and steroid hormones. Estrogen increases vasodilation by producing endothelium-derived nitric oxide. This hormone also increases the expression of heat shock proteins, acts as an antioxidant, and affects inflammation with cytokines associated with the function of the immune system [28], [29], [30], [31].

Pascal et al. investigated the effects of anthropometry and sex steroids on gender differences in the stiffness of large vessels and pressure dynamics from childhood to old age. They suggested that the increased stiffness of large vessels and pulse pressure are important risk factors for cardiovascular diseases. There are gender differences in the biomechanical properties of large vessels throughout life. Women show more vessel stiffness than men before puberty. This stiffness significantly increases after menopause. Men experience a linear increase in arterial stiffness after puberty. This indicates that women have larger and stiffer vessels than men. However, these effects are decreased by sex steroids during the fertile years [20]. In a study with the aim of determining the gender differences in the outcomes of coronary interventions in 17 hospitals in the United States, Duvernoy et al. suggested that the prevalence of vessel complications following the interventions was significantly higher in women than in men [32]. Collier et al. studied the gender differences in resting blood flow and vessel stiffness during four weeks of resistance training (including 10 movements in 3 sets with 10 repetitions) and aerobic training (including 30 minutes of walking on a treadmill with maximum heart rate of 65%) in four groups of men and women (40–60 years old) with mild hypertension. They showed that resistance training reduced systolic and diastolic pressure more in women than in men. In addition, the men undergoing resistance training had a higher central flow velocity (carotid and femoral arteries) and a higher vessel stiffness index. Moreover, the maximum volumetric blood flow in the femoral artery of the resistance training group was higher than that of the aerobic group. They stated that the increase in volumetric flow was potentially caused by the increase in vasodilation as a supportive mechanism. The increase in volumetric flow reduced central blood pressure and increased vessel stiffness [33]. In comparing the responses of men and women with peripheral vascular disease to a cardiac rehabilitation program, Shabani et al. showed that both groups were probably equally affected by the rehabilitation exercise program (including treadmill and arm and leg ergometers) [34]. Studying the effect of eight weeks of resistance training on the lower limbs of 21 young and healthy subjects (11 males and 10 females), Stebbings et al. suggested that this training significantly increased the resting diameter and blood flow velocity in carotid and femoral arteries. They observed a significant decrease in the diameter and blood flow velocity of both arteries after four weeks of detraining [35].

At first glance, it seems that the effect of the combined aerobic-resistance training on improving the conditions of patients following coronary artery angioplasty is different in men and women. However, few studies have been conducted on this group of patients with cardiovascular diseases to confirm this hypothesis. Moreover, few researchers have investigated gender differences and particularly the variables discussed in the current research. On the other hand, although the studies conducted in this field have shown that a combined training program is safe and improves the functional status and quality of life of patients with cardiovascular diseases in both genders, there are still many differences among these studies in terms of the intensity, duration, and optimal type of training program to gain the maximum advantages of such programs. Previous studies have shown that blood flow behavior and the structural function of the vessels have a direct relationship with the process of atherosclerosis. This relationship can be predicted by observing the vascular structure and blood flow through Doppler ultrasound [36]. The existing studies have more investigated and compared the process of atherosclerosis in the coronary, aortic, and carotid arteries of healthy and sick individuals. They have not investigated the peripheral vessels such as the brachial and femoral arteries or middle-aged patients very much though these patients have coronary stenosis and the process of atherosclerosis may have also spread to their peripheral arteries [37]. Therefore, considering the effectiveness of training, the present research aimed to determine the effect of eight weeks of concurrent (aerobic-resistance) training on the selected variables of blood and vascular biomechanics in the left femoral artery in middle-aged patients (40–65 years old) following coronary artery angioplasty with an emphasis on gender.