Nigerian Journal of Clinical Practice

ORIGINAL ARTICLE
Year
: 2019  |  Volume : 22  |  Issue : 12  |  Page : 1765--1771

Isometric handgrip exercise training attenuates blood pressure in prehypertensive subjects at 30% maximum voluntary contraction


GU Ogbutor1, EK Nwangwa2, DD Uyagu3,  
1 Department of Physiotherapy, Federal Medical Centre, Asaba, Nigeria
2 Department of Human Physiology and Family Medicine, College of Health Sciences, Delta State University, Abraka, Delta State, Nigeria
3 Department of Family Medicine, University of Benin Teaching Hospital, Benin City, Nigeria

Correspondence Address:
Dr. E K Nwangwa
Department of Human Physiology and Family Medicine College of Health Sciences, Delta State University, Abraka, Delta State
Nigeria

Abstract

Background: Prehypertension highlights a category of subjects who are at high risk of developing hypertension. Aim: This study assessed the blood pressure attenuating effect of isometric handgrip exercise in the management of prehypertension. Materials and Methods: A total of 400 prehypertensive subject with a mean age of 40 ± 10 years and recently diagnosed as prehypertension were recruited for the study. They were randomly distributed into exercise and control groups (n = 200). The control group was placed on lifestyle modification only, while the exercise group performed a 24 consecutive days isometric hand grip exercise training at 30% maximum voluntary contraction (MVC) for 2 min each day in combination with lifestyle modification protocol. Results: The results show a statistically significant reduction in systolic blood pressure (SBP) and diastolic blood pressure (DBP). The exercise group had a mean reduction of 7.48 ± 0.06 and 6.41 ± 1.01 mmHg of the SBP and DBP, respectively. It was further observed that both the SBP and DBP and pulse rate significantly increased acutely within 5 min post exercise at 30% MVC with a mean value of 8.60 ± 0.20 mmHg, 7.33 ± 0.03 mmHg, and 8.24 ± 0.20 beats/min of the SBP and DBP and pulse rate, respectively. However, this increase returned to pre-exercise value within 10 min post exercises to a mean value of −0.68 + 1.64 mmHg, 1.48 ± 1.02 mmHg, and 3.00 ± 0.11 beats/min, respectively. Conclusion: This study has shown that isometric handgrip exercise is effective in the attenuation of blood pressure in prehypertensive subjects especially when combined with the routinely recommended lifestyle modifications. However, caution should be taken when recommending it because of acute increase in blood pressure.



How to cite this article:
Ogbutor G U, Nwangwa E K, Uyagu D D. Isometric handgrip exercise training attenuates blood pressure in prehypertensive subjects at 30% maximum voluntary contraction.Niger J Clin Pract 2019;22:1765-1771


How to cite this URL:
Ogbutor G U, Nwangwa E K, Uyagu D D. Isometric handgrip exercise training attenuates blood pressure in prehypertensive subjects at 30% maximum voluntary contraction. Niger J Clin Pract [serial online] 2019 [cited 2022 May 22 ];22:1765-1771
Available from: https://www.njcponline.com/text.asp?2019/22/12/1765/272203


Full Text



 Introduction



Hypertension constitutes a major socioeconomic burden all over the world, ranking as the third leading cause of death globally.[1] The number of people affected has been estimated to be over 1 billion and this number is projected to increase to 1.56 billion in 2025.[2] Hypertension and its complications contribute significantly to worldwide morbidity and mortality and it is the major cause of stroke, kidney disease, and cardiac failure.[3],[4],[5] More than 60% of the world population is said to be affected directly or indirectly; therefore, a serious challenge in the prevention and management is created.[6] Despite the increased knowledge of the need to prevent hypertension and the claims of the availability of various forms of antihypertensive agents, the disease remains prevalent.[7] Drugs have been the main stay of management of hypertension, but the cost, availability, and adverse effects are the contending issues. It has been reported that drugs have not been able to control about 47% of the affected hypertensive patients.[8]

Studies have shown that there is a high risk of cardiovascular events in prehypertensives and an increasing rate of progression to hypertension.[9],[10] The Seventh Report of the Joint National Committee (JNC) on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure reported that prehypertension accounts for 62% of cerebrovascular disease and 49% of ischemic heart disease.[11] However, the 2014 JNC 8 and 2017 AHA/ACC guideline for the diagnosis of hypertension led to an increase in the number of Americans who are classified hypertensive from 32% to 46% of the population.[12] This is due to a change in the baseline value for definition of hypertension as blood pressure >130/80 mmHg instead of >140/90 mmHg previously used. Several global committees have recommended life style modification as a means of stemming the progression of prehypertension.

The drawback and inadequacy of the currently accepted therapeutic regimen for hypertension has led to the need for effective, safe, easily accessible, and cost-efficient, nonpharmacological protocol, and isometric hand grip exercise is one promising protocol, which needs to be explored.[13]

Physical activity has been shown to have an independent long-term potency of lowering blood pressure and has therefore been recommended as a nonpharmacological option for management of hypertension.[14] The current challenge to the scientific community is developing and implementing effective clinical and public health measures that could lead to sustainable lifestyle change.

Dynamic exercise is physically demanding, lacks objective quantification, cumbersome, and so difficult to prescribe. These have made compliance very difficult. However, the available data are scarce with regard to the recommendations for isometric exercise. Isometric exercise is performed all over the world as part of activities of daily living at home or in the offices regardless of blood pressure levels. In addition, daily activities, such as lifting, holding, and carrying of items, involve isometric exercises. Therefore, isometric exercise could be less hazardous than previously presumed. Studies revealed that blood pressure increase is specifically determined by the mode of muscle contraction and also proportional to the percentage of maximum voluntary contraction (MVC) rather than the absolute amount of force produced. It further stated that blood pressure elevation is proportional to the percentage of MVC used by the most vigorously contracting muscle and that the contractions of other muscles are not additive.[15]

Notable limitations which included lack of standardization of training procedures and quantification of exercise have precluded a conclusive inference on the use of isometric exercise in the management of prehypertension. This study, therefore, tried to eliminate these flaws and investigate the effectiveness of a quantifiable, cost-effective, personalized, less demanding, and safe exercise protocol in the management of hypertension. It is, therefore, expected that the findings from this study will add to the existing body of knowledge on the effects of isometric exercise training at 30% MVC on the blood pressure.

 Materials and Methods



Study location

The study was carried out at a Federal Medical Centre. The hospital is a Federal tertiary health institution which occupies a strategic position as it receives referrals from peripheral hospitals.

Sample size determination

The sample size was calculated using the formula for a population >10,000:

n = Z

2pq/d

2[16]

where n = the sample size, p = the proportion of the population estimated to have the condition, q = (1- p), Z = 95% confidence interval set at 1.96, and d = the degree of accuracy usually set at 0.05.

At a prevalence of 58.7%,[17]

n = 1.962 (0.587) (0.413)/0.052

=0.9313/0.0025

372.5 = 373

With a 10% attrition rate added, a sample size of 400 subjects was recruited.

Study design

It was a randomized controlled trial involving 400 subjects who were recruited from the adult population of prehypertension subjects who visited the medical consultant clinic. A screening session was conducted to assess the blood pressure of potential candidates based on the classification of the JNC on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure.[11] This represents a systolic blood pressure (SBP) range of 120–139 mmHg and diastolic blood pressure (DBP) range of 80–89 mmHg. All blood pressure measurements were taken according to JNC 7 guidelines, which require the subjects to rest in a quiet environment for at least 10 min prior to the measurement with a digital sphygmomanometer. There was no gender discrimination. Participants were recruited through physician's referral who meet the inclusion criteria. All participants recruited were untrained which was defined by a score of 3 or less using the Rapid Assessment of Physical Activity survey.

The procedure of this study consists of an isometric handgrip exercise group and a control group who were age-, weight-, and height-matched. In all, 400 prehypertensive males (n = 213) and females (n = 197), ages of 40 ± 10 years, were recruited for the study. All subjects were free of cardiovascular diseases, renal disease, diabetes, and were not on any medications that affect the blood pressure.

The subjects were randomized by asking them to pick from a ballot box with concealed papers marked EG (exercise group) or CG (control group). Proper education on the need to adopt appropriate lifestyle and detailed procedure of the isometric hand grip exercise was given to the subjects before commencement of the study. The subjects in the CG were placed on lifestyle modification protocol, while the subjects in the EG were placed on isometric hand grip exercise in addition to lifestyle modification protocol. The blood pressure and compliance with lifestyle modification were monitored for 24 days and data were collected for analysis.

Selection criteria

Only subjects whose blood pressure values met the JNC 7 definition of prehypertension and who were neither on antihypertensive nor had other comorbidities were recruited for the study.

Procedure

The subjects were asked to squeeze the dynamometer with their dominant hand twice, for a maximum of 2 s with a 5-min rest; so as to determine their respective MVC for each session. The mean of the two readings was taken as the MVC for each subject for that session. Subjects were thereafter instructed to squeeze and sustain the dynamometer for 2 min at determined 30% MVC. The dynamometer pointer which read the scale gave a visual feedback to the subjects for the maintenance of the 30% MVC. This procedure was repeated twice for each training session with a 5-min rest. The position adopted by the subjects throughout the exercise training was sitting with the upper limbs supported on a table. The exercise protocol was done for 24 consecutive days. To avoid the extreme pressor responses elicited by fatiguing isometric efforts, the isometric exercise training used in this study consisted of brief handgrip contractions separated by rest periods. In addition, the ethical principles were considered thereby allowing the exercise group participants to adopt lifestyle changes concomitantly with the exercise as it is unethical to deny this group of patients the recommended therapy.

Data collection

The age, sex, weight, height, initial resting blood pressure (IRBP), final resting blood pressure (FRBP), and acute cardiovascular response (ACVR) were recorded. The data were statistically analyzed using the descriptive and inferential statistics. One-tailed Student's t-test was used to determine the intra- and intergroup differences. The SPSS version 21.0 statistical package was used. P ≤ 0.05 was considered statistically significant.

Ethical approval

Written informed consent was obtained from the subjects and the study was approved by the Research and Bio-ethics Committee of both the hospital and the College of Health Sciences.

 Results



The descriptive statistics of the biodata and anthropometry of the subjects are as shown in [Table 1]. A total of 400 prehypertensive adults with a mean age for the control and exercise groups as 41.27 ± 6.31 and 40.78 ± 6.04 years, respectively, were analyzed. The control group included a total of 200 participants involving 112 (56%) males and 88 (44%) females, while the exercise group was made up of a total of 200 participants, 109 (54.5%) males and 91 (45.5%) females. The control group recorded a mean weight of 76.03 ± 9.43 kg and a mean height of 1.62 ± 0.95 m giving a total body mass index of 31.02 ± 3.72 kg/m2. The exercise group had a mean weight of 75.49 ± 9.80 kg and a mean height of 1.65 ± 0.09 m with a body mass index of 27.74 ± 3.19 kg/m2.{Table 1}

In addition, the IRBP and FRBP changes in the control and exercise groups and comparison of blood pressure reduction within groups are as presented in [Table 2].{Table 2}

A statistical significant reduction occurred in both the SBP and DBP of the control and exercise groups; however, the reduction was higher in the exercise group.

In addition, the comparative analysis of the blood pressure reduction between the exercise and control groups is as shown in [Table 3].{Table 3}

This implies that the difference in blood pressure reduction between the exercise (7.47 ± 1.69 mmHg) and control (4.07 ± 2.61 mmHg) for SBP and 6.42 ± 1.01 mmHg and 3.89 ± 1.62 mmHg for diastolic groups was both statistically significant. It is noteworthy to report that the exercise group had a greater reduction in blood pressure values.

This aspect of the study was to assess the ACVR of participants in responses to isometric hand grip exercise at 30% MVC after 5 min [Table 4]. A mean value of 8.6 ± 0.20 mmHg, 7.33 ± 0.03 mmHg, and 8.24 ± 2.19 beats/min statistically significant increase was observed in the SBP, DBP, and pulse rate, respectively. The values indicate that a statistical significant difference (P < 0.05) exists in initial and final cardiovascular parameters.{Table 4}

Furthermore, the acute cardiovascular responses 10 min post isometric hand grip exercise at 30% MVC were studied [Table 4]. The SBP reduced by 0.68 mmHg below the initial value, while the DBP and pulse rate returned to an approximate value of 1.48 mmHg and 3.00 beats/min higher than the initial resting values, though it was only the pulse rate change that was statistically significant.

 Discussion



The focus of this study was to determine the cardiovascular response to isometric handgrip exercise on blood pressure of prehypertensive subjects. It revealed that lifestyle changes significantly reduced the blood pressure within a duration of 24 days. The significant difference observed between the exercise and control groups clearly indicates that blood pressure reduction is enhanced when the routinely recommended lifestyle modification is combined with isometric hand grip exercise training. The results also provide evidence on the safety and effectiveness of isometric hand grip exercise therapy in the attenuation of blood pressure in prehypertensive subjects.

The isometric exercise in combination with lifestyle changes significantly reduced both the SBP and DBP by a mean value of 7.47 ± 1.69 and 6.42 ± 1.01 mmHg, respectively, compared with the value of the control group of 4.07 ± 2.61 and 3.89 ± 1.62 mmHg, respectively. This reduction is clinically significant as it has been shown that a reduction of 5 mmHg can decrease the risk of stroke by 40% and heart disease by 15%–20%.[18] This finding is in tandem with a study by Kelley and Kelley,[19] who reported that the average range of SBP and DBP decrease is between 3 and 8 mmHg and 2 and 6 mmHg, respectively.

In this study, participants performed two bouts of isometric hand grip exercise training for 24 consecutive days at 30% MVC for 2 min with in-between rest period of 5 min. The exercise protocols in this study were modeled after isometric handgrip training studies, such as those conducted by Wiley et al.,[20] who reported a significant decline in both SBP and diastolic resting blood pressures, with group averages of 12.5 and 14.9 mmHg, respectively,[21] and who observed a 5 mmHg reduction in diastolic pressure and a 4 mmHg reduction in the mean arterial pressure, and a 3 mmHg reduction in SBP. A major difference between their works and this study is the large population of participants recruited in this study which makes generalization of the findings more acceptable. This study also used a shorter duration because of the need to know the minimum duration required to have a significant reduction in the cardiovascular parameters.

The results obtained in this study further support previous works which investigated the effects of isometric hand grip exercise therapy on the resting blood pressure.[22],[23] In a study, 10 prehypertensive participants achieved an average reduction of 13 mmHg in SBP following 6 weeks of isometric hand grip training 3 days per week at 50% MVC.[24] However, the results of these studies could not be generalized due to the small sample size of participants recruited in their study and it may be possible that a greater value of reduction obtained was due to the longer duration of their study.

Furthermore, isometric exercise has previously been associated with exaggerated hypertensive responses.[25] This often anticipated acute increase in the blood pressure response to isometric hand grip exercise which has placed restrictions on its recommendation as a form of antihypertensive therapy was observed to be statistically significant at 30% MVC in this study. There was an acute increase within 5 min of the exercise of 8.6 ± 0.20 mmHg, 7.33 ± 0.03 mmHg, and 8.24 ± 2.19 beats/min for SBP, DBP, and pulse rate, respectively. This implies that caution should be applied on its recommendation for patients with highly elevated blood pressure. However, the results further revealed that within 10 min post exercise, the SBP had reduced to −0.68 mmHg below the pre-exercise level, the DBP had returned to 1.48 mmHg above the pre-exercise level, and the pulse rate has also returned to 3.00 beats/min above the pre-exercise level. This study supports the previous works which claimed that the blood pressure rise quickly returned to pre-exercise levels. According to MacDougall et al.,[26] the blood pressure returns to normal limit, 10–15 min after exercise.

Other investigators who studied this phenomenon by having their patients grip a hand dynamometer at 30% MVC found that the arterial pressure reached 200/135 mmHg and quickly returned to control levels after the exercise.[27] It is believed that the blood pressure rise during the handgrip was caused by an increase in cardiac output, because the heart rate and stroke volume both increased and the peripheral vascular resistance either did not change or showed a slight decrease. This further confirms that isometric exercise is associated with acute hemodynamic changes consisting of increases in SBP, DBP, and mean arterial pressure and also an increase in heart rate and cardiac output.[13]

The importance of life style modification in the management of elevated blood pressure cannot be overemphasized. Some previous works examined the effectiveness of specific lifestyle changes.[28] A systematic review of randomized controlled trials provided a summary table on the average effect of lifestyle intervention on blood pressure and concluded that regular aerobic exercise, weight loss of 3%–9%, reduced salt diet, dash diet, and alcohol moderation effectively reduce blood pressure (systolic/diastolic) by approximately −5/−4, −11/−5.5, −3/−3, −5/−3, and − 4/−2.5, respectively.[29]

Limitation of study

This study was conducted for a duration of 24 days and it established the efficacy of isometric hand grip exercise training in achieving a significant reduction in the SBP and DBP. This study did not establish the long-term effect and other records of the parameters of vascular health and function, and hence the need for further study.

 Conclusion



This study concludes that isometric handgrip exercise significantly reduced the SBP and DBP as well as the pulse rate in prehypertensive subjects, within 24 days of the study duration at 30% MVC. There was a significant acute elevation in the blood pressure and pulse rate 5 min post exercise, which, however, returned to resting level within 10 min post exercise. Therefore, the prescription of isometric hand grip exercise in addition to other lifestyle modification should be encouraged, though caution should be observed in those with highly elevated blood pressures.

Recommendation

The available evidence has proven that isometric hand grip exercise is efficacious in the attenuation of blood pressure especially when combined with the routinely recommended lifestyle modifications. Therefore, isometric handgrip exercise at 30% MVC, in combination with lifestyle modification, should be recommended to patients with prehypertension and be part of a comprehensive treatment regimen. Future research into the effect of exercise discontinuation and long-term effect on the achieved reduction in the blood pressure is recommended. In addition, a study may be designed to record other parameters of vascular health and function such as pulse wave velocity, arterial distensibility, reactive hyperemic forearm blood flow, flow-mediated vasodilatation, and venous compliance.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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