Hypertension is one of the most common diseases worldwide. A prevalence of hypertension is around 30.0~45.0% of adults, rapidly increasing with aging [1]. Also in Korea, the prevalence of hypertension in people over 30 years was 28.3% and the prevalence in the elderly was 64.3% [2]. Essential hypertension that accounts for 95% of all hypertension cases has no identifiable cause, and is considered a primary risk factor that provokes various kinds of complications including cardio-cerebrovascular disease, peripheral vascular disease and/or renal disease [3, 4]. Although hypertension is required to be managed actively as a typical chronic disease that is a primary risk factor of cardiovascular disease, stroke, etc. [5], blood pressure (BP) control rate of hypertensive patients was as low as 45.4% [2]. It is generally known that lowering 10 mmHg in systolic BP may reduce 20.0% cases of cardiovascular disease, 17% of coronary artery disease, 27.0% of stroke, 28.0% of heart failure, and 13.0% of the total mortality rate [6], and therefore blood pressure control of hypertensive patients plays a vital role to prevent heart disease or cerebrovascular disease.

Once diagnosed with hypertension, lifestyle modification is encouraged to begin first as a nonpharmacological treatment prior to pharmacotherapy [7]. Among the nonpharmacological treatment methods, regular physical activity has been emphasized, and regular aerobic exercise is accordingly been encouraged [7, 8]. Any sport or activity that works large groups of muscles, is continually maintained and performed rhythmically, is defined as an aerobic, or cardiovascular, exercise by the American College of Sports Medicine (ACSM). Aerobic exercise reduces risk of cardiovascular disease as well as controlling BP, and therefore is now actively recommended especially in the European and US hypertension guidelines [5, 9].

Increased heart rate (HR) has been associated with high blood pressure and risk factors for accidental cardiovascular disease because it is associated with an imbalance in the autonomic nervous system that can affect blood pressure [10, 11].

For such reasons, many studies of effects of aerobic exercise on BP and HR of hypertensive patients have been performed, but results of its characteristics and effectiveness varied depending on each study [A1–A37]. Types of aerobic exercise recommended to hypertensive patients include walking, running, bike-riding, aerobic dance, dance, swimming, etc. [3]. Among these, a number of studies including walking and running were conducted [A1–A3], while studies applying water-based training including swimming and aquarobic [A4,A5] and other various types of aerobic exercise including bike-riding [A6,A7] and dance [A8,A9] have also been conducted. Effects of moderate-intensity exercise have been reported in a greater number of studies of aerobic exercise for hypertensive patients [A3,A5,A10,A11], while some studies introduced effects of vigorous-intensity [A7,A12] and low-intensity [A13,A14] aerobic exercise. Frequency of aerobic exercise provided to hypertensive patients widely ranged from two to five days weekly and durations spanned between 4 weeks and 37 weeks [12]. Still, optimal exercise programs structured for hypertensive patients have not been clearly established [13]. Thus, it is necessary to examine the effects of aerobic exercise provided to hypertensive patients and determine the most effective exercise program for reducing BP.

There have been several systematic reviews with meta-analysis of studies that examined effects of aerobic exercise on hypertensive patients [14, 15, 16, 17]. These studies included only some of types of aerobic exercise [14, 15] or other interventions such as diet with aerobic exercise [14]. One paper [15] included non-randomized controlled trials (RCTs) studies. Also most of these studies [14, 15, 17] have not been analyzed according to the characteristics of exercise. In only one study [16], the effect on BP was analyzed according to exercise characteristics, but not only patients with hypertension but also normotensive persons and other interventions other than aerobic exercise were included. Another recently published study [17] reported that the number of papers was small and the heterogeneity was high, and also additional study with larger sample sizes to compare exercise characteristics should be considered.

Thus, the aims of this study were to (1) identify effects of aerobic exercise on hypertensive patients, and, further, to (2) compute effect sizes that would impact on systolic and diastolic BP by exercise characteristics such as types, intensity, frequency and duration, and (3) verify its effects on heart rate, by systematically reviewing and conducting meta-analysis for studies with RCTs.

In order to examine closely the effects of aerobic-exercise intervention on BP and HR of patients with hypertension, in this study, a systematic review and meta-analysis have been performed. The total number of studies included in the systematic review was thirty-seven, which represent that a considerable number of studies of effects of aerobic exercise on hypertensive patients have consistently been conducted. Especially articles published after 2010 comprised 67.6% of all the studies selected, and this suggests that studies of effects of aerobic exercise on hypertensive patients have aggressively been carried out in recent years. Regarding types of aerobic exercise, exercise including walking and running made up more than half at 54.1%. Börjesson et al.'s [12] systematic review including 27 studies and of Whelton et al.'s [16] study for meta-analysis reported similar results to our study. It is presumably because those types of exercise can be simply prepared, cost-efficiently used and easily accessed [23]. Another feature found in the systematic review was that participants of more than half i.e. four out of 6 studies of water-based training were women-only, and no studies with men-only participants have been found. Water-based training was the most effective in reducing blood pressure, but it was only for women, so it is necessary to investigate whether there is a difference by gender. Also, participants of three out of 5 studies of dance were elderly or women. Such findings suggest that types of exercise applied differs depending on the characteristics of participants. Although our results show effect size of BP was different by types of exercise, all types of aerobic exercise were found to be effective to lower BP, and therefore it would be desirable for an optimal type of aerobic exercise to be recommended to hypertensive patients considering their preference. Over two-thirds of the literature selected in this study used moderate-intensity exercise that accorded with Börjesson et al.'s [12] study that reported a majority of literature applied moderate- intensity intervention. This is presumably because ACSM generally recommends its moderate-intensity to patients with hypertension rather than prohibiting aerobic exercise. But vigorous- intensity exercise was also effective, so it may recommended with considering the risk to benefit ratio.

Effect sizes of systolic and diastolic BP after aerobic exercise were − 8.29 mmHg and − 5.19 mmHg respectively, similarly to some preceding studies [13, 14] that performed meta-analysis of aerobic-exercise effects on BP. Aerobic exercise may decrease BP by reducing sympathetic activation, vasoconstrictor tone of the vascular endothelial cells and cardiac output, and increasing vessel diameter, which would lead to reduction of peripheral vascular resistance [24, 25].

In regards to types of exercise, all types of aerobic exercise including bike-riding, dance, walking/running, and water-based training helped lower both systolic and diastolic BP. The finding is meaningful that all types of aerobic exercise had effects on reduction of BP. In order to induce continuous and active participation in aerobic exercise, various environmental factors such as provision of exercise information, removal of exercise obstacles, and consideration of individual differences must be considered, but the autonomy of individuals participating in exercise, that is, self-determination, is an important factor. The group who chose the preferred type of exercise, that is, the group with high self-determination, perceived exercise positively, had high exercise persistence, and had a high physical and physiological effects [26]. Therefore it would be advisable, based on scientific ground, to provide selections of various aerobic-exercise types depending on each patient's preference. For example, a patient who is a senior or has a joint health problem is recommended to try water- based training rather than walking or running that can put stress on weight-bearing joints. Regular aerobic exercise help lower BP, and accordingly it is very important to generate excitement about the exercise. In other words, patients' engagement rate would increase by suggesting their preferred type of aerobic-exercise intervention to each individual [27].

As to effect size by exercise intensity, low-intensity aerobic exercise had no impact on reduction of systolic and diastolic BP, whereas moderate- and vigorous-intensity had an effect. Moderate- intensity exercise for hypertensive patients also is recommended by ACSM. But the results differ from ones of Whelton et al. [16] that low-, moderate- and vigorous-intensity exercises were all effective to lower BP. In this study [16], only 19 out of 47 studies were subject to hypertension. And when analyzing the difference in BP according to exercise intensity subgroup, it was not mentioned how many hypertensive participants were included. Therefore, it is not recommendable that low-intensity aerobic exercise is effective in hypertensive patients.

In terms of effect size by exercise frequency, each group who performed exercise twice, three times, or four times or more per week had the benefit of lowering systolic and diastolic BP although intergroup differences were statistically non-significant. Amount of exercise is associated with the product of frequency, intensity, and time [8]. Unexpectedly, participants who performed exercise twice weekly were found to have effect size as large as ones of groups who participated in exercise three or four times weekly. This is presumably because two-thirds of articles in twice-a-week groups performed vigorous-intensity exercise.

As to effect size by exercise duration, both systolic and diastolic BP significantly decreased in all groups, and aerobic exercise that lasts more than about 8 weeks may have a better antihypertensive effect. These results correspond to ones of the preceding studies that represented BP would begin to decrease 6~8 weeks following onset of exercise [28]. But, our results were different from Cao et al. [17] that compared three groups of exercise duration divided into less than 8 weeks, 8~12 weeks, and more than 12 weeks, with results that group of less than 8 weeks had the largest decrease in BP, and longer duration led to smaller blood-pressure-lowering effects. However, Cao et al. [17] pointed out their limitation that very small number of literatured was only included for analysis.

Thus, selected exercise according to individual's preference should be regularly performed for 8 weeks or longer three times weekly with moderate-intensity or twice weekly with vigorous- intensity in order to maximize effects of aerobic exercise on BP.

Mean effect size of heart rate following aerobic exercise was − 4.22 beats/min, which showed aerobic exercise helped to decrease heart rate. Although there have been a considerable number of individual studies regarding effects of aerobic exercise on heart rate of hypertensive patients, only one of them has conucted meta-analysis, and its result showed the effect size was − 4.94 beats/min [17], which corresponded to our analysis results. Higher heart rate is linked with cardiovascular disease as well as hypertension, and therefore it would be very meaningful result that aerobic exercise decreased heart rate of patients with hypertension [29]. Sympathetic activity, in particular, that commonly occurs in hypertensive patients may be controlled and parasympathetic nervous system may be activated, which would result in heart rate deceleration [30].

There have been a number of studies that performed meta-analysis depending on categories of exercise (e.g. aerobic exercise, strength exercise, and complex exercise), but only few studies verified the effects based on classified variables including types, intensity, frequency and duration of aerobic exercise. In this light, our study that computed each effect size depending on aerobic exercise characteristics has implications. Our findings will be the basis of intervention for patients with hypertension who can select any preferred type of aerobic exercise among walking, running, bike-riding, dance, swimming or aquarobic, etc. It is also expected that this results will be a guidance of interventions or studies of aerobic exercise for hypertensive patients.

Our study has several limitations. First, this study included articles published in Korean or English only, and therefore studies that would possibly reflect characteristics of participants from other cultural areas may have unfortunately been left out. Second, there were only two articles that included low-intensity exercise, and so direct comparison of effect sizes was restricted unlike moderate- or vigorous-intensity exercise. Third, although RCTs were only included, effect-size heterogeneity of exercise types, intensity, frequency and duration was measured to be moderate or higher. Therefore, the results should be interpreted with caution. Still, our results are considered highly reliable because RCT studies with considerable quality of evidence were only selected in this study and any publication bias was not identified.

This results showed that aerobic exercise had impact on reduction of BP and HR of hypertensive patients. It is recommended to select an exercise according to the individual's preference, but if there is no preference, water-based exercise with the greatest drop in blood pressure can be more recommended. Although vigorous-intensity exercise was effective in lowering blood pressure, the risk to benefit of hypertensive patients should be considered when performing vigorous-intensity exercise. Frequency is recommended to perform 3 times per week or 2 times with vigorous-intensity. Also it is effective to keep the period longer than 8 weeks. In conclusion, aerobic exercise can be recommended in a variety of clinical settings to lower BP and HR in hypertensive patients.