Effect of physical training on the blood pressure of adolescents with obesity

Instituição: Escola Superior de Educação Física da Universidade de Pernambuco (ESEF/UPE), Recife, PE, Brasil 1Mestrando em Hebiatria pela UPE, Recife, PE, Brasil 2Graduação em Bacharelado em Educação Física pela UPE, Recife, PE, Brasil 3Doutor em Nutrição pela Universidade Estadual de São Paulo “Júlio de Mesquita Filho” (Unesp); Professor Adjunto da UPE, Recife, PE, Brasil 4Doutor em Educação Física pela Universidade de São Paulo (USP); Docente do Curso de Educação Física da Universidade Estadual de Londrina (UEL), Londrina, PR, Brasil 5Doutor em Saúde Pública pela USP; Professor Adjunto da UPE, Recife, PE, Brasil ABSTRACT

In this context, it is necessary to summarize the data about the effects of physical training on the blood pressure of obese adolescents, aiming to identify the factors related to such differences. Therefore, this study aimed to analyze, using a systematic review, the effects of physical training on the blood pressure of obese adolescents.

Methods
The main outcome of this review was the change in the blood pressure of obese adolescents after a physical training program. We performed a systematic review of the original studies published in journals indexed in PubMed/MedLine (National Library of Medicine), LILACS (Literatura Latino-Americana e do Caribe em Ciências da Saúde), SciELO (Scientific Electronic Library Online) and ISI Web of knowledge SM electronic databases, which analyzed the effects of physical training on the blood pressure of obese adolescents.
The keywords used in the electronic research were defined in consultation to the Medical Subject Headings (MeSH) on the U.S. National Library of Medicine (NLM) website and to the DeCS -Describers in Health Sciences (Descritores em Ciências da Saúde) in the Health Virtual Library (Biblioteca Virtual em Saúde -BVS). The keywords were divided into four blocks, and then combined, as shown in Figure 1.
The electronic search in the databases was performed using the combination of the keywords and the application of limits, with the inclusion of studies that: evaluated subjects between 10 and 18 years old; were published up to 2010; were performed in humans; were randomized clinical trials; and were controlled.
By reading the titles and abstracts retrieved in the first search, we included studies that met the following criteria: the sample was constituted of obese adolescents, regardless of whether the studies included other age groups; the blood pressure was measured; and the study included a non exercise control group.
In the following step, we performed the full reading of the articles and data extraction. In this step, besides the outcome, we also extracted the data that could have affected the main outcome, such as the sample characteristics, the body mass, the exercise protocol and complementary interventions. We also performed the analysis of the studies quality using the PEDro score (33) . This score consists of 11 questions, with scores ranging from zero (minimum) to ten (maximum).
All the steps (electronic search in the databases, selection and evaluation of the potential studies, data extraction and analysis of the studies quality) were performed by two independent investigators, and the results of each phase were compared by a third investigator, who evaluated the agreement between the pairs. If disagreements were found, the third investigator was responsible for the final analysis.
Five studies used some kind of complementary intervention (19,(28)(29)(30)(31) , with the dietary intervention being the most common ( Table 2). The duration of training ranged from 8 to 48 weeks. Regarding the exercises protocol, two studies used strength exercises combined with aerobic exercises (21,22) , while six used aerobic exercises only. Three of these studies combined walking with sporting activities (22,28,30) .Most studies used a three weekly sessions schedule lasting from 40 to 90 minutes each, with intensities from 55 to 95% of the maximum heart rate. Table 3 shows the results of the effects of training on blood pressure. Four studies observed a decrease in the systolic blood pressure in the training group compared with the control group (19,(28)(29)(30) , while four other studies did not show any difference (20)(21)(22)29) . Two studies (29,30) observed a decrease in the diastolic pressure and one study (30) showed a decrease in the mean blood pressure in the training group when compared with the control group. The four studies that showed a decrease in the systolic blood pressure also found a decrease in body mass.

Discussion
The main findings of this study were: the effects of physical training on the blood pressure of obese adolescents are controversial, the decrease in the blood pressure resulting from physical training seems to occur concomitantly with the reduction in the body mass; and the studies that observed a decrease in the blood pressure with physical training used an exercise schedule consisting of three to six weekly sessions of aerobic exercises lasting from 50 to 90 minutes each, with intensity of 55 to 75% of the maximum heart rate, and training duration ranging from 12 to 24 weeks.
For this review, we performed a literature search in the PubMed/MedLine, LILACS, ISI and SciELO databases, which represent the main sources of original scientific data in health sciences. The search showed that articles on the theme were only identified at PubMed/MedLine and ISI. These results emphasize that original information on the effects of physical training on the blood pressure of obese adolescents are not conveyed in the Latin American literature, so that professionals who are interested in obtaining information on the subject must necessarily consult the databases in the English language.
The results of the studies that analyzed the effects of physical training on the blood pressure of obese adolescents showed great controversy. Of the eight studies that evaluated the effects of physical training on the systolic pressure, only four found a significant decrease. Likewise, only some of the studies that evaluated the effects on the diastolic and mean pressure showed a reduction of these variables in response Tjona et al (20) 2009 Training   to physical training. This controversy seems to be directly related to changes in the body mass resulting from physical training. Actually, all the studies that observed a reduction in the systolic blood pressure also showed a reduction in the body mass, and in two of them (30,31) the changes in both variables were correlated. The decrease in blood pressure mediated by the reduction of body mass can be explained by mechanical (lesser mechanical compression of the fat mass on the blood vessels), metabolic (reduction of leptin levels (37) and insulin resistance (38) ), inflammatory (decrease in pro-inflammatory agents (39) ) and neural (decrease in the sympathetic nerve activity (40) ) factors. These results emphasize the importance of the reduction of the body mass in the decrease in blood pressure, which reinforces the importance of the dietary intervention in the treatment of the obese adolescent (41)(42)(43) .
Based on the summary our findings, we identified a great variability in the training protocols used, which may also have contributed to the controversial findings. From the eight studies included, for instance, five used aerobic exercises only, while two used a combination of aerobic training with strength exercises, and only one applied an interval aerobic training. The intensity ranged from 55 to 95% of the maximum heart rate, and the duration of each session ranged from 40 to 90 minutes. It is suggested that the reduction in blood pressure mediated by the physical training results from several factors, such as: improvement in the endothelial function (21) , reduction in the cardiac sympathetic tone (44)(45)(46) , increased sensitivity of the cardiovascular reflexes (47) and decrease in leptin levels (48)(49)(50) , among others. However, these factors seem less important for the decrease in blood pressure then the reduction of the body mass, since not all the studies that used physical training showed a decrease in blood pressure.
The analysis of the study protocols that found a reduction in blood pressure shows some common points: all of them used at least three sessions of aerobic exercises per week, lasting from 50 to 90 minutes, with intensities from 55 to 75% of the maximum heart rate. Furthermore, no differences in blood pressure were observed in the studies with training duration less than 12 weeks. Therefore, training programs that aim the reduction in the blood pressure of obese adolescents should be based on these training protocols.
Some limitations of the present study should be considered. The literature search was performed in journals indexed in the PubMed/MedLine, LILACS and ISI databases only. It is, thus, possible that some studies on the theme may have not been included. It is noteworthy, however, that the databases used in our study are the most used for searching articles in both Portuguese and English languages. Also, the literature search did not include the databases of theses and dissertations, which could possibly have limited the number of studies included. Finally, the search used only keywords in Portuguese and English only, and studies published in other languages were not included.
The results of this review indicate that there is no consensus in the literature about the cardiovascular effects of physical training on the blood pressure of obese adolescents. Nevertheless, it was possible to identify that studies that showed a decrease in the blood pressure also observed a reduction in the body mass, using protocols of three to six weekly sessions of aerobic exercises lasting from 50 to 90 minutes, with intensities from 55 to 75% of the maximum heart rate, and duration of training ranging from 12 to 24 weeks. In spite of these results, one should take into account that that the well planned physical training should be stimulated in this population regardless the blood pressure response in the view of the other positive effects related to training on the reduction of cardiovascular risks.