This systematic review with meta-analysis aimed to analyze the effects of aerobic training, with and without progression, on the SBP and DBP of hypertensive adults. Our main results show that both aerobic training strategies (with and without progression) were effective in reducing BP and that older age is a factor associated with greater BP reductions due to aerobic training in hypertensive individuals.
The general results of the present study (aerobic training vs. control group) are in line with results from other meta-analyses, which showed an average reduction of 8 to 12 mmHg in SBP and 5 to 6 mmHg in DBP in hypertensive adults11–13. Thus, our results reinforce the importance of aerobic training as a primary strategy for the treatment of hypertension, since the reduction in BP resulting from this practice is similar to that achieved with treatment with antihypertensive drugs47. These results are clinically relevant since a 10 mmHg decrease in SBP is associated with a 20% reduction in the risk of developing cardiovascular disease, 27% in the occurrence of stroke and 13% in the risk of mortality48.
Although there is no difference in the BP reduction between aerobic training with and without progression, reductions of greater magnitudes occurred in studies that progressed in the duration and intensity variables separately. The studies that progressed in intensity25,26,29–31,33 showed reductions of 12.89 mmHg (SBP) and 7.09 mmHg (DBP) and achieved the highest percentages of intensity compared to the other studies. Studies that progressed in duration28,32, on the other hand, showed reductions of 13.98 mmHg in SBP and 5.07 mmHg in DBP, and achieved the longest durations in comparison to all studies with and without progression. The studies that progressed in both23,24,27,28,34 showed more modest reductions in SBP (8.28 mmHg), with no significant reduction in DBP, and achieved session durations longer than the other studies, however the percentage of intensity was below that observed in general, both in with progression and without progression studies. Although the greatest reductions in SBP occur with studies that have progressed in duration, it is possible that the intensity of training is an important modulator of BP reduction, since both studies that have progressed in duration and those that have progressed in intensity have achieved or maintained a high intensity of training. In addition, our results showed a response of greater magnitude in studies with progression in duration, for SBP, and in intensity, for DBP, which may be associated with different mechanisms of action. Bearing in mind that the performance of these mechanisms in response to training is still unknown49, it is not possible to state the reason associated with these differences.
The literature points to exercise intensity as a determining factor for BP changes in response to training programs7,50, indicating a dose–response relationship, so that higher intensities of trainig promote greater reductions in BP51. As for the duration of the session, there seems to be no dose–response relationship, as longer durations do not necessarily indicate greater reductions in BP, with beneficial effects occurring even with shorter periods of exercise52. However, although some studies have investigated the effects of different intensities and durations of exercise, there is insufficient evidence to determine the relationship of these variables with the BP response53, especially when not analyzed as isolated doses, but in relation to their manipulations throughout interventions. In the general analysis of our results, the greatest reduction occurred in the study by Meirelles et al. (2009)30, both for SBP (-26.3 mmHg) and for DBP (-13.4 mmHg), having reported progression in intensity and reached high intensity (85% HRmax). In addition, although there was no progression in duration, the length of the sessions was intermediate when compared to the other studies (40 minutes).
Although the evidence regarding progression is not concrete, the manipulation of training variables, such as duration and intensity, are recommended, and must respect a gradual process20, especially in intensity progression50. This strategy, in addition to reducing the risks of musculoskeletal injuries and cardiovascular events, favors greater participation by the participant in training20. In addition, other precautions must be considered in this process, such as the levels of BP the person has, recent changes in antihypertensive drugs, effects caused by exercise and medications, in addition to the presence of other diseases and related conditions50.
With regard to the subgroup analysis by sex, the effects of the interventions were effective for both men and women, and, in absolute terms, the magnitude of reduction observed for women was greater in SBP (11.98 mmHg) and DBP ( 5.81 mmHg), although there was no statistical difference between the groups. Turnbull et al.54, in a meta-analysis, demonstrated that men and women have BP reductions of similar magnitudes, thus demonstrating that training methods do not need to differ between sexes. For analysis between practitioners with and without comorbidities, both groups showed significant BP reductions, with similar magnitudes. This finding demonstrates great clinical relevance, considering that hypertensive patients with comorbidities, which present more serious health risks and greater chances of developing coronary artery disease (CAD)55, benefit from the training as much as those without comorbidities.
Regarding the results by users and nonusers of antihypertensive drugs, both showed significant and similar reductions in SBP and DBP, emphasizing that aerobic training also has great hypotensive potential, being able to further optimize the treatment of hypertension, reducing the risks of complications and improving the clinical picture of hypertensive patients56. Reinforcing these results, the meta-regression analysis showed that the use of antihypertensive drugs was not a moderator in reducing BP during aerobic training. However, different dosages and classes of antihypertensive drugs were used in the studies included in this review, which makes it difficult to understand the effects of these factors on the pressure responses observed. Similar to our results, meta-analysis by Sardeli et al.57 also found that medication use did not affect BP reduction in response to training. However, this result was not specific to aerobic training and included few studies. Studies evaluating the effects of drug therapy and exercise on BP variables mainly focus on outcomes separately and have conflicting results. Thus, the evidence regarding the interaction between the use of medications and pressure responses to exercise is still scarce53.
With regard to the duration of the interventions, it was shown that regardless of the aerobic training being performed for short or long periods (< 12 weeks, 12–24 weeks and > 24 weeks), the BP reductions are similar. Likewise, a systematic review by Cao et al.13 demonstrated that interventions of less than 8 weeks, between 8 and 12 weeks and of more than 12 weeks were similarly effective in decreasing BP. On the other hand, Cornelissen and Smart (2013)11 observed that aerobic training periods of less than 12 weeks produced greater reductions in SBP and DBP when compared to longer periods, which could be related to the greater adherence of participants to shorter. However, we should consider the importance of the continuity of the training, in order to maintain the benefits achieved. Considering the divergence of the available findings, there is a need for more studies with good methodological quality to better understand the role of the duration of the intervention in the nondrug treatment of hypertensive patients.
As for the training methods, the continuous and the interval methods promoted similar reductions in SBP (-10.62 mmHg; -10.32 mmHg, respectively) and DBP (-6.10 mmHg; -4.62 mmHg, respectively), showing that both are effective. Another recent meta-analysis, carried out with the hypertensive population58, showed reductions in SBP for both training methods when compared to control groups (continuous: -3.70 mmHg; interval: -5.64 mmHg), but without difference between training groups. For DBP, reduction was also found after continuous (-2.41 mmHg) and interval (-4.80 mmHg) training when compared to control groups, but the magnitude of DBP reduction in the interval method was significantly greater when compared to the continuous one.
Regarding the training modality, our study shows that the SBP and DBP reduce in a similar way regardless of whether the aerobic exercise is performed with walking / running (-11.20 mmHg), on cycle ergometers (-10.89 mmHg) or combining the training modalities (-11.12 mmHg). This finding has an important practical application, as it demonstrates that exercise professionals can choose the form of aerobic exercise according to the patient’s preference, thus being able to favor adherence due to the ease of access to a certain modality or to specific clinical conditions (i.e., using a cycle ergometer due to difficulty mobility with support of their own weight), without prejudice to the reduction in BP.
As for the training location, conducting training in water may be an alternative for the hypertensive population, as it has also shown slightly higher magnitudes of BP reductions (SBP - terrestrial: -11.06 mmHg; aquatic: -12.01 mmHg; DBP - terrestrial: -6.23 mmHg; aquatic: -7.94 mmHg) in absolute terms, without statistical differences. Another study of systematic review also observed that training in water reduces SBP and DBP in a similar way to terrestrial training in adults and the elderly, with 54.5% of the sample classified as hypertensive and 27.3% with pre-hypertensive59. It is noteworthy that studies comparing exercises performed in different media and evaluating different outcomes in hypertensive patients are still scarce, especially in the case of chronic effects.
The meta-regression analysis showed a significant association only for age and SBP responses, indicating that older individuals showed greater magnitude reductions in SBP after aerobic training. Since the prevalence of hypertension is higher at older ages60, the results of the present study suggest that the practice of aerobic training is an important nondrug strategy for reducing BP in the elderly, which has been observed previously61. However, our results were different from those evidenced by previous studies11,57,62. There is still disagreement in the literature regarding the influence of age on the effects of BP reduction in response to aerobic training, so that other factors must also be considered.
An important point to be highlighted in the present study is that most studies analyzed with progression used HRmax to prescribe the intensity of exercise23–25,27−30,33,34 while only one study without progression used this method38. Since HRmax is a marker with limitations, we can explain, in part, why the studies that performed progression did not find greater chronic reductions in BP, since the prescribed intensity may have been underestimated in these studies. That is, not progressing violates a training principle, but using more suitable methods for prescribing intensity (such as VO2max and HRres) seems to mitigate the effects of the lack of progression in training.
Finally, our study exposes some limitations that need to be highlighted. Although the general analysis has a considerable number of studies, some subanalyses were carried out with a small number of studies. When assessing methodological quality, the set of studies analyzed did not clearly report most of the information, and of the five evaluation criteria, three were reported unclearly in more than 50% of the studies, making it difficult to assess the risk of bias. Another limitation is related to the lack of important information in the studies, which prevent association with the results, such as disease duration, antihypertensive drugs used and the training status of the participants.
On the other hand, the present study has some strengths. As far as we know, this is a first meta-analysis that assesses the effects of the progression of aerobic training in patients with hypertension, with a significant number of participants being analyzed. The analysis of possible moderators of the effect using the meta-regression analysis is also a strong point of the study. In practical terms, although some guidelines recommend the progression of training, more precise information is lacking in relation to the way to progress. In this regard, the present study presents results that will possibly assist in the prescription of exercises, such as manipulation and the increase of the variables of the training, especially session length and intensity, thus maximizing the beneficial effects of exercise on BP.