The findings of the present research showed that concurrent (endurance-resistance) exercises lead to non-significant improvements in forced vital capacity (FVC), forced expiratory volume in one second (FEV1) and forced expiratory volume in one second to forced capacity (FEV1/FVC). ) and maximum oxygen consumption (VO2MAX) was disabled in young women. Also, after the training period, there was no significant change in the first ventilation break point (VT1), second ventilation break point (VT2), respiratory exchange ratio (RER), heart rate (HR), ratio of oxygen consumption to heart rate (VO2/HR) in Inactive young women were observed. The effect of concurrent (endurance-resistance) exercises on the cardiorespiratory function of sedentary people has been limited. It depends on physical fitness (22). It can be said that the effectiveness of exercise training is due to improving the strength and endurance of the respiratory muscles, reducing inflammation and subsequently reducing the resistance of the airways. These factors will reduce the apparent resistance of ventilation and will allow to increase efficient ventilation with less effort. Increasing the strength of respiratory muscles and reducing airway resistance during exercise is effective in improving lung function. In explaining the reasons for the effect of exercise on FVC and FEV1 following exercise, it should be said that the weakness of respiratory muscles including the diaphragm, muscles between Ribs and abdominal muscle groups change the values of FVC and FEV1 and forced expiratory volume in one second to forced capacity, as well as increasing The remaining volume as a result of expiratory muscle weakness and neuromuscular disorders along with reduced lung elasticity and limited are among the factors that reduce FVC values. On the other hand, it has been found that neuromuscular coordination and greater activity of the diaphragm muscle improve these components (23). Therefore, aerobic training has probably led to the improvement of these indicators through the above mechanisms, however, a longer training period may be needed to have a significant effect on these indicators.
VO2max, also known as functional aerobic capacity, indicates the maximum amount of oxygen used by exercising muscles and is considered the gold standard measure of the functional limitation of the cardiorespiratory system. The results of the current research indicated a non-significant improvement of VO2max after concurrent exercise (endurance and strength at the same time). The findings of Gabler et al. (2018), Faton et al. (2010), Eschuman et al. (2015) and Prastesh (2018) have reported a significant increase in VO2max after concurrent exercise (endurance and strength at the same time).(16, 17, 21, 24).
Among the possible reasons for this increase in the maximum level of oxygen consumption, we can mention an increase in blood volume, an increase in the end-diastolic diameter, a better blood flow to the active muscles, an increase in the density of capillaries and mitochondria in active muscles after exercise (25). Maximum oxygen consumption is significantly influenced by several factors such as genetic structures, growth, body composition and physical activity (26). Also, the increase in maximum oxygen consumption can be due to the decrease in body fat percentage. Lean tissue is much more metabolic than adipose tissue. An increase in the ratio of lean tissue to fat is associated with an increase in the relative maximum rate of metabolism even in the absence of exercise (27). Contrary to the findings of our study, some studies have shown that a combination of endurance and strength training in a training program when the total number of weekly training sessions is high leads to impaired strength development and muscle hypertrophy (19). One study has shown that VO2max decreases after a long period (20 weeks) of concurrent endurance and strength training in men (20). The inconsistency of the obtained results may be due to the different methods used. Even in some cases, the different conditions of the subjects in terms of age, gender and level of physical fitness may be effective in the heterogeneous results. Factors affecting RER during exercise, such as duration and intensity of exercise, age, sex, fitness level, muscle glycogen, and daily dietary intake, together explain only 60% of the variation in RER during exercise, and usual dietary intake Food has a greater effect on RER than carbohydrate consumed during exercise. More research is needed in women, especially regarding the RER response to exercise. It also appears that there is individual variation in substrate oxidation during exercise in both untrained (28) and trained subjects (29).
It has been found that during exercise, the increase in sympathetic activity causes the release of adrenaline and noradrenaline, resulting in an increase in myocardial contractions and an increase in heart rate. During exercise, by increasing the mean arterial pressure, the pressure receptors in the arteries by sending a negative feedback decrease the sympathetic activity and as a result increase the diameter of the vessels, increase the volume of blood available to the muscles, decrease the blood pressure and decrease the heart rate (30). Exercise is accepted as a way to lose weight and improve body composition (31). In the present study, a non-significant decrease in enterometric indices was observed. As a result of aerobic and resistance sports activities due to increased mitochondrial density, the capacity of oxidative enzymes increases in muscles. In addition, increasing the activity of the electron transfer chain enzymes increases the activity of enzymes involved in the oxidation of fats and also the activity of lipoprotein lipase (32). As a result of aerobic training, the density of beta-adrenergic receptors on the cellular surface of fat tissue increases and as a result their sensitivity to the lipolysis process increases. It seems that the main driver of this process is the distribution of catecholamines due to aerobic activity and increased oxidation of fats. (33). Therefore, the body weight of the subjects decreases. In the research of Sarmidian and Sohri (2015), 10 weeks of aerobic activity (with an intensity of 65 to 75% of the maximum heart rate) and resistance (with an intensity of 55 to 65% of one repetition maximum) with moderate intensity had no effect on weight in postmenopausal women. They stated that the reason Its possibility can be caused by insufficient intensity and duration of exercises to create desirable changes (34). It is possible that the intensity of the exercises in the present study was not suitable for weight loss. It is possible that concurrent exercises can lead to a greater reduction of fat percentage and improvement of muscle mass, especially in obese subjects, by activating fat tissue more and affecting the enzymes involved in fat metabolism compared to endurance and resistance exercises alone. Perhaps the most common reason and mechanism for justifying the improvement of body composition, the reduction and improvement of muscle mass as a result of resistance training is that following the stimulation of muscle protein synthesis and the increase of fat-free body mass as a result of resistance training, the rate of resting metabolism increases and this causes an increase in total energy consumption. Resting time and negative change in energy balance and therefore reducing fat and its total reserves in the body (35). Therefore, adding this type of training to endurance training will probably bring more benefits. Generally, it is possible to reduce WHR with long-term and hard training. The lower the intensity and duration of exercise, the smaller the decrease in WHR (36). Therefore, it may be interpreted that the intensity and duration of the exercises of the current protocol were not enough to significantly reduce WHR. One of the limitations of the present study is the small number of samples, so a similar study with the measurement of these indicators in a high number of samples is suggested. Also, future studies should consider a longer period of time and a higher intensity to investigate the pulmonary function response to concurrent exercise.