Dose‐effect relationship between brisk walking and blood pressure in Chinese occupational population with sedentary lifestyles

Abstract The purpose of this study was to explore the effects of brisk walking on blood pressure (BP) in Chinese Han occupational populations to identify the appropriate volume of exercise needed for BP management. Eight‐hundred and two office staff with sedentary lifestyles were recruited to receive a prescription pedometer‐assisted brisk walking intervention for 3 months. To evaluate exercise intervention efficiency using statistical methods, the effective steps was divided as follows: 4000‐ < 8000 (Level 1), 8000‐ < 10 000 (Level 2), 10 000–12 000 (Level 3), and > 12 000 (Level 4) steps/day. The data of 688 participants who completed the study were analyzed. After intervention, Systolic BP (SBP) and Diastolic BP (DBP) at Levels 1–3 were significantly decreased (p < .05). For participants with hypertension at baseline, all four levels demonstrated a significantly reduced SBP and DBP. In addition, there was a significant dose‐effect relationship between the effective steps and the SBP. Compared with the maximum effective steps level (Level 4), the average change of SBP between level 1–3 and level 4 were statistically significant, with ‐3.24 mm Hg (95%CI: ‐5.74 to ‐0.74, p = .011), ‐2.58 mm Hg (95%CI: ‐4.73 to ‐0.43, p = .019), and ‐2.19 mm Hg (95%CI: ‐4.20 to ‐0.18, p = .033), respectively. For the hypertensive cohort, only the difference between Level 1 and 4 was statistically significant (Level 1 vs. Level 4: difference in means = ‐6.22 mm Hg, 95%CI: ‐12.68 to ‐0.24, p = .036). No significant dose‐effect relationship of DBP was observed. Our findings showed brisk walking can effectively control BP in Chinese populations and a significant dose‐effect relationship was found between exercise and SBP.


INTRODUCTION
The prevalence of hypertension is increasing yearly, with worldwide cases estimated to increase by 15-20%, to 1.5 billion by 2025. 1 According to the Chinese Hypertension Survey, from 2012 to 2015, approximately 244.5 million Chinese people aged ≥18 years suffered from hypertension. 2 Hypertension, especially elevated systolic blood pressure (SBP), is a key risk factor for morbidity and mortality worldwide, with approximately 9 million deaths attributed to the condition each year. [3][4][5] Although cardiovascular and cerebrovascular diseases, hypertensive cardiovascular diseases, have become a major economic burden worldwide, 3,6 their prevalence may be reduced through efficient control of hypertension, their most preventable risk factor. 7 Multiple studies have shown that increasing physical activity can significantly reduce SBP and diastolic blood pressure (DBP), 8,9 thereby significantly reducing the incidence of both cardiovascular and cerebrovascular events in patients with hypertension; thus, improving quality of life and reducing the burden of disease. 4 week; equivalent to brisk walking for at least 3000 step counts per day (a minimum of 100 steps/min for at least 30 min). 14 However, these guidelines do not explicitly indicate the upper limit of exercise required to improve health outcomes, or the effects of exercise duration on health benefits, especially in relation to cardiovascular health.
Although the positive effects of increased exercise on blood pressure (BP) and other cardiovascular disease risk factors are well established, there is limited research investigating the optimal amount of exercise required to prevent or control hypertension across various ethnic groups, sexes, ages, and occupations; thus, necessitating further study. Herein, we investigate the optimal amount of exercise required to prevent or control hypertension in the Chinese Han office worker population, thereby providing a scientific basis for the application of exercise interventions in BP management in the Chinese population.

Study design
This study included all participants in the brisk walking intervention, and those with under or beyond physical activity recommendations were considered as the reference group (control group). Furthermore, this is a self-controlled study, in which participants acted as their own controls when pre-intervention and post-intervention BP were measured. Prior to intervention, all participants were educated in the dietary management of BP via a single information session. Next, each participant was prescribed a 3-month pedometer-assisted, selfmonitored walking intervention.

Brisk walking intervention program
Exercise intervention program is based on open-ended walking interventions in a real world. Brisk walking was the chosen form of exercise in this study. An exercise suggestion is proposed to participants based on their original physical activity levels (PALs), and the established internet-based exercise and nutrition health management application and a prescription pedometer were used to implement the exercise intervention, as well as to guide and record all involvements in exercise. 15 The intervention program included an exercise intensity (moderate walking speed of 80-90 meters/min for females (4.0-4.5 MET) and 90-100 meters/min for males (4.5-5.0 MET) 16  Although this 30-min could be completed in one or several sessions, the duration of each continuous exercise was to be a minimum of 10 min. In the second or third months, exercise targets were gradually increased according to the previous month's completion. In principle, the exercise intervention program in this study met the recommended amount of exercise set by the guidelines for the management of hypertension. 1

Measurements and procedures
All participants underwent outcome measurements at baseline and study completion.

Walking evaluation
Step counts accumulated with a frequency of 100-150 steps/min were considered as "effective steps" and recorded using a prescription pedometer. 15 Participants were, therefore, required to wear a pedometer daily throughout the trial period. Additionally, each participant's walking program was recommended for 30-80 min/day; thus, the recommended number of effective steps was 3000-12 000 steps/day. Thus, for statistical analysis, we divided the effective steps achieved by each participant into the following four levels: 4000-< 8000 (Level 1), 8000-< 10 000 (Level 2), 10 000-12 000 (Level 3), and > 12 000 (Level 4) steps/day. As Level 4 was beyond physical activity recommendations, it was established as the reference group against which the efficacy of the intervention, and thus the recommended amount of exercise, was evaluated and verified.

Diet scores
The eating behavior section of the Healthstyle: A Self-Test 18

Participant characteristics and exercise performance
Of the 802 patients recruited to this study, 114 withdrew due to personal reasons ( Figure 1); data of the remaining 688 participants, The study flow diagram 331 males and 357 females, were analyzed. The average age was 37.0±9.9 years, with no significant differences between sexes (p = .54).
General participant characteristics at baseline are shown in Table 1, with significant differences existing between the height, BW, BMI, WC, and BF% (p < .05) of males and females. 17.0% (117/688) of participants had a diagnosis of hypertension; 49 of which were undergoing antihypertensive therapy.

Effects of brisk walking on BP and its dose-effect relationship
For all participants, as shown in Table 2, the effective steps at Level 1-3, both of SBP and DBP were significantly reduced after 3 months The BP change was taken as the dependent variable, and the possible related factors of BP changes were taken as independent variables for multivariate analysis, as shown in Table 3. In the analysis, the entry regression method was used to fit the model, and the test level was 0.05. There was a dose-effect relationship between the change of SBP and the effective steps ( Data are expressed as mean ± SD. a Effective steps levels, Level 1: 4000 -< 8000 Steps/day; Level 2: 8000 -< 10 000 Steps/day; Level 3: 10 000-12 000 Steps/day; Level 4: more than12 000 Steps/day. Abbreviations: BW, body weight; DBP, diastolic blood pressure; N, number of participants; SBP, systolic blood pressure; Δ, is a 3-month change. Data are expressed as mean difference (95% confidence interval). a Effective steps levels, Level 1: 4000 -< 8000 Steps/day; Level 2: 8000 -< 10 000 Steps/day; Level 3: 10 000-12 000 Steps/day; Level 4: more than 12 000 Steps/day. b ΔSBP: difference of systolic blood pressure change in mm Hg (95% confidence interval). c ΔDBP: difference of diastolic blood pressure change in mm Hg (95% confidence interval). Data are expressed as mean difference (95% confidence interval). a Effective steps levels, Level 1: 4000 -< 8000 Steps/day; Level 2: 8000 -< 10 000 Steps/day; Level 3: 10 000-12 000 Steps/day; Level 4: more than 12 000 Steps/day. b ΔSBP: difference of systolic blood pressure change in mm Hg (95% confidence interval). c ΔDBP: difference of diastolic blood pressure change in mm Hg (95% confidence interval).
difference of SBP changes between Level 1 and Level 4 was significant (-3.95 mm Hg, 95% CI: -7.35 to 0.55, p = .024). For female, it only Level 2 showed a significant difference (-3.41 mm Hg, 95% CI: -6.48 to -0.34, p = .030). However, there was no significant dose-effect relationship between the effective steps and the changes of DBP.

Effect of different effective steps levels on blood pressure of hypertensive and non-hypertensive participants
According to the presence of hypertension, participants were divided into the hypertensive and the non-hypertensive groups for subgroup analysis (Table 5). For the hypertensive cohort, after 3 months of brisk walking, SBP and DBP both significantly decreased at Levels 1 to 4 (p < .05). For non-hypertensive cohort, SBP decreased in levels 1-3; however, only Level 2 (-2.2±9.1 mm Hg, p = .004) was significant. On the other hand, Level 4 had a significant increase (2.0±10.2 mm Hg, p = .015). The change of DBP was not significant.
The multiple linear regression model was used to analyze the relationship between BP and exercise. The results show that there was a significant dose-effect relationship between the change in SBP and the effective steps (Table 6). Compared to Level 4, only the difference of Level 1 is statistically significant, which is -6.22 mm Hg (95% CI: -12.68 to -0.24, p = .036); the other levels were not significantly different.
There was no significant dose-effect relationship between DBP and the effective steps. For the non-hypertensive, as shown in Table 5, there was a significant dose-effect relationship between the change of SBP and the effective steps, but no significant dose-effect relationship was found in DBP.

DISCUSSION
This study showed that 3 months of brisk walking, with a pace of 100-150 steps/min, can effectively contribute to BP improvement in Chinese Han occupational populations with sedentary lifestyles.
Moreover, we identified a significant dose-effect relationship between changes in SBP and effective steps, but not in DBP.
The key focus of this trial was to motivate all participants to alter their sedentary lifestyles. But for most people, changing their routine habits may be difficult. However, since walking is an essential daily activity, the use of walking-based aerobic exercises, such as brisk walking, is an ideal intervention to encourage adherence to moderateintensity movement suitable for most physically inactive people. 19 Indeed, this study shows that a brisk walking intervention may be appli-

This study is based on open-ended walking interventions in a real
world, so that their exercise is highly independent and random. In the statistics and analysis of the dose-effect relationship, the effective steps that they actually walked daily were divided into four levels of 4000-< 8000, 8000-< 10 000, 10 000-12 000, and > 12 000 steps/day, and observed their effect on BP, as well as their differences.
We found that for both male and female participants, an effective steps level of more than 12 000 steps per day appeared to be detrimental in the control of SBP as an increase in the mean SBP level was demonstrated in these participants. In order to clarify whether excessive exercise is beneficial to control BP, the effective steps > 12 000 steps/day, which was beyond physical activity recommendations, was considered as the reference group. We found that 4000-< 8000, 8000-< 10 000, and 10000-12 000 steps/day had significantly better effect on reducing SBP than that by > 12 000 steps/day for all participants. In the male cohort, only the effective steps range from 4000 to < 8000 steps/day showed a better reduction in SBP; while in the female cohort, the effect of reducing SBP at 8000 to < 10 000 steps/day was better. Therefore, regardless of sex, the effective steps level of > 12 000 steps per day did not show a better reduction of SBP. These results further suggest that more than 12 000 effective steps per day did not show better control of SBP. However, the increase in SBP caused by exercise is one of the major contribution of cardiovascular and cerebrovascular events. 20  There are several possible mechanisms of the lesser effects of greater exercise on lowering BP. Firstly, we have to mention the formation mechanism of systolic pressure, that is, the rapid injection of blood in the ventricles of the heart during contraction, resulting in lateral pressure on the blood vessel walls. In order to maintain BP during exercise, the heart has to pump out more blood (cardiac output).
Greater exercise, either intense or prolonged, places greater stress on the cardiovascular system and increases cardiac output. This results in an adaptive change in the heart's structure known as ventricular hypertrophy or dilation. Such conditions have been reported in studies involving athlete. [24][25][26] But whether the change is physiological or pathological remains to be seen. In addition, this may be because the maintenance of BP during exercise depends on the excitement of sympathetic nerves. Long-term exercise keeps the sympathetic nerves at a high level of excitement for a long time, so that the excitability of sympathetic nerves at rest may also increase adaptively. [27][28][29] The SBP of individuals who exercised a lot was not reduced much or increased instead. However, a clearer mechanism still needs to be further verified by more studies.
Interestingly, increasing the amount of exercise did not lead to better SBP control, regardless of sex and presence of hypertension. Moreover, uncontrolled excessive exercise may increase the risk of exercise injuries or cardiovascular events. Additionally, excessive exercise may lead to less adherence to exercise routines, leading to exercise dropout. As mentioned in the review by Berge and coworkers, 30 the incidence of hypertension in athletes with a large amount of exercise training is significantly higher compared to athletes with a small amount; therefore, greater amount of exercise is not necessarily better for BP control.
This study has practical implications for BP management in Chinese occupational populations with sedentary lifestyles, as it provides evidence for the appropriate amount of exercise required to control BP across sexes and different BP status groups. Several limitations exist in this study. First, participants did not exercise strictly in accordance with the amount recommended in the intervention, often blindly increasing their amount of walking; thus, resulting in a relatively small percentage of participants performing 4000-8000 steps/day. In addition, participants' salt intake, smoking, and alcohol consumption were not required or recorded; and only a pre-intervention health education on the risk factors of hypertension and related diet was conducted for all patients.

CONCLUSIONS
Exercise in the form of brisk walking may effectively improve BP control in Chinese Han occupational populations with sedentary lifestyles.
A significant dose-effect relationship was found between exercise and BP, with the highest exercise level seems to be detrimental to the control of SBP, especially in individuals with a history of hypertension.