Acute Effect of a Session of Resistance Exercises Using the 80% 1RM Circuit Method on Blood Pressure

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Introduction
According to the Brazilian Society of Arterial Hypertension (2008), there are 600 million hypertensive patients in the world, and it also states that the prevalence of hypertension in Brazil is high, because among adults, 30% to 35% have the disease. As a consequence of this increase in blood pressure levels, the target organs are exposed to serious risks of commitment to increased cardiovascular risk. This increase in blood pressure may have as causes sedentary lifestyle, stress, inadequate eating habits and alcohol and tobacco consumption, which are characteristics derived from the urbanized and post-technology established lifestyle [1]. In view of this reality, it becomes evident the need for interventional approaches in an attempt to prevent and treat hypertension [2]. To achieve these objectives, it has been widely recommended by health professionals, along with pharmacological treatment, adherence to a healthy way of life and regular practice of physical exercises, as effective ways to slow down blood pressure levels [3]. Numerous studies prove the benefits that are offered by physical exercises, both in the prevention and treatment of this disease. Because they are characterized by a situation that removes the organism from its homeostasis, causing several physiological adaptations that are necessary and, among them, those related to cardiovascular function during the ex-ercício [4].
Currently, resistance physical exercises have been used in programs that promote, when adequately supervised, significant benefits and low risks to the practitioner, contributing to the reduction of resting rial art pressure (Bermudes, 2004). Doederlein, et al. [5] indicate that a safe method for conducting a training is by giving additional elements to the manipulation of variables adjunct to their absolute and relative intensity (type of exercise, recovery interval, number of repetitions and sets, mobilized load and execution speed). However, some studies have shown that the intensity of exertion does not influence the hypotensive response after exercise [6] and on the other hand, other investigations have shown that the intensity of exercise can influence the size and duration of the blood pressure response [7]. According to the authors, the physical quality involved in this type of physical activity is muscle strength, which, in addition to being necessary in development, is, in terms of health promotion, a fundamental parameter for the practice of occupational and leisure activities, For a broader discussion on the effects of exercise on blood pressure, it is worth noting that it can be influenced not only by the adaptations resulting from chronic physical training (chronic adaptations), but also by the influence of a single exercise session (subacute or post-exercise effects) [8]. In a study conducted by Cornelissen, et al. [9], composed of 12 analyses and 341 volunteers, a reduction in systolic blood pressure and diastolic blood pressure values was demonstrated for individuals who were exposed to resistance training. The same study describes that no differences were observed related to exercise intensities, as well as the use of conventional or circuit resistance training. Since, in conventional training, all the series of a given exercise are performed before starting the next one and, generally, there are higher loads and interval time than in the circuit method, where it is more continuous and with shorter interval time, since the execution is a single series in each station, passing the next exercise immediately, and repeating the circuit more often if necessary. Although resistance training, similarly to aerobic training [10], causes only minimal decreases in blood pressure levels, in population terms this consequence may have an impact on a lower incidence of coronary artery disease and stroke [11]. Thus, the present study aims to compare the behavior of blood pressure after a resistance exercise session in the circuit method, using a load of 80% of one the maximum repetition -1RM with the pre-exercise situation.

Methodology
The study included 12 normotensive male volunteers, aged 24.9 ± 2.43 years, practicing resistance exercises for at least six months and practicing these activities at least three times a week. Exclusion For the comparison of blood pressure before and immediately after the measurements obtained, the Student "t" test was used for dependent samples. All procedures were performed in the Statistic for Windows 6.0 Software and the level of significance adopted was p<0.05. Table 1 presents the general characteristics of the sample, with mean values and standard deviation of age (Table 1). Table   2 shows the results of the "t" test to compare the mean values (± standard deviation) for systolic and diastolic blood pressure at rest and immediately after a resistance exercise session in the 80% 1RM circuit method. According to the results, it was observed that systolic blood pressure after the exercise session was significantly higher than that observed at rest. However, no difference was observed in diastolic blood pressure values immediately after exercise ( Table 2).

Discussion
The present study compared the blood pressure condition before and immediately after a session of resistance physical exercise in the circuit method with 80%of 1RM. According to the results of the research, it was observed that immediately after exercise the mean systolic blood pressure was significantly higher than the means preceding exercise. This result is explained in part by the activation of chemoreceptors due to peripheral fatigue [13].
Considering that the 80% load of 1RM can be classified as a high intensity, these results corroborate the literature, which indicate that exercises performed until exhaustion would result in a higher blood pressure response immediately after exertion [14]. However, it should be considered that the results of the present study are limited to comparing resting blood pressure and immediately after exercise. The literature also points out the acute benefit in blood pressure control in normotensive individuals [6]. The decrease in blood pressure levels after resistance exercise is proven by the highlights of other recent autores, which conducted studies in normotensive and hypertensive patients of different age groups [15,16]  pressure and heart rate tend not to change or even the increase, mainly in maximum request efforts [18].
Among the most important chronic adaptations resulting from the regular practice of strength exercises, the possible reduction of the frequency of the dyad deficit [21] and resting blood pressure [22] can be cited [22], and also the least cardiac overload during exercise, with lower double-product associated [23]. When it comes to the training volume, it is two to five times a week. For Santarém (2001), the effectiveness of training requires relatively high weights with few repetitions, provided that no maximum effort is made, blood pressure increases within safe levels, which is in ac line with the objective proposed by the present study, where a higher load of 80% of 1RM was used in a circuit method.
The author adds that it is wrong to say that light weights and a greater number of repetitions are safer, because when isometry and nea occur, at the end of the series blood pressure would increase more than with greater weight and fewer repetitions. There is a lot of evidence and studies that point to resistance training as beneficial and safe even for people with heart disease, provided that it is prescribed with the care necessarily considered [28][29][30].

Conclusion
According to the results, it is concluded that the exercise resisted at 80% of 1RM in the circuit method, causes a significant increase in SBP immediately after its execution. It is suggested to carry out future studies that follow the recovery period after exertion, in order to verify if there would be any hypotensive effect for the practitioner, as well as to apply resistance exercise in the prevention and non-pharmacological treatment of arterial hypertension.