|Hyptertension and Exercise
Gavin C. Hillman and Len Kravitz, Ph.D.
Hypertension is a widespread health problem effecting nearly 25% of the adult population in the United States (Fang et al. 2005). The importance of treating this silent killer lies in its associated risk to cardiovascular disease, the number one cause of death in America, as well as other maladies including renal disease, stroke, heart failure, and peripheral artery disease. Although hypertension is defined as systolic blood pressure (SBP) equal to and greater than 140 and/or diastolic blood pressure (DBP) equal to and greater than 90 mmHg, risk factors of hypertension can be seen in blood pressure (BP) as low as 115/75 mmHg and will begin to double in risk for every 20/10 mmHg increase (Pescatello, Franklin et al., 2004). The new classification of pre-hypertensive (SBP 120-139 and DBP 80-89 mmHg) has been introduced to identify individuals who are at a higher risk of developing hypertension, pointing out an important fact that hypertension is a modifiable risk factor.
Exercise as a lifestyle modification is beneficial to a wide variety of health conditions. Specific to hypertension, the benefits of exercise have been promoted by a number of organizations and agencies including the American Heart Association, the American College of Sports Medicine, the Surgeon General of the United States, The National Institutes of Health, and the Centers for Disease Control (Wallace, 2003). Although hypertension studies are ongoing, there is an ample amount of research support that provides clear evidence of the positive effects of exercise on lowering persons with hypertension. This research update will discuss the role of exercise intensity and modality, the combining efforts of diet and weight loss, exercise as a preventative measure, as well as some underlying physiological mechanisms.
Exercise Intensity and Duration: How Hard and for How Long?
Most exercise prescriptions for hypertensive patients include a duration of 20-60 minutes of aerobic exercise at 40-70% VO2max performed 3-5 times a week (Wallace, 2003). Several studies confirm the results of low to moderate training being just as efficient in lowering BP compared to high intensity (>70% VO2max) cardiovascular exercise (Halbert et al., 1997). The fitness level of the individual may also play a central role in determining optimal intensity. A recent study of 49 middle-aged men with high-normal (SBP=130-139 mmHg; DBP=85-89 mmHg) to Stage 1 (SBP=140-159 mmHg; DBP=90-99 mmHg) hypertension, randomly assigned to a light (40% VO2max) or moderate (60% VO2max) exercise protocol, found reductions in BP from the lower intensity were more prevalent in the older, less fit male subjects; whereas the moderate intensity exercise was more effective in the physically fit men (Pescatello, Margauz et al., 2004). Although more research is needed to better specify an optimal exercise intensity to reduce BP, the general guidelines of moderate intensity exercise performed for 30 minutes or more on most days of the week are appropriate for successfully lowering elevated blood pressure levels, and can be readily implemented for many populations of men and women. Moderate exercise programs are also maintained easier and impart less musculoskeletal injury for previously sedentary populations, who are not accustomed to vigorous physical exertion.
Exercise Mode: What is Best?
There is a significant amount of evidence that aerobic training helps to reduce BP. In a meta-analysis (a statistical technique that combines the results of several studies) of 54 clinical trials, findings (in hypertensive men and women) included a reduction in SBP by an average of 3.84 mmHg and 2.58 mmHg for DBP (Whelton et al., 2002). In addition to aerobic exercise, many people are now enthusiastically participating in resistance exercise. Although there is relatively little research on blood pressure and resistance exercise as compared to aerobic training/blood pressure studies, one recent meta-analysis found a decrease of 3.2 mmHg and 3.5 mmHg for systolic and diastolic BP, respectively (Cornelissen & Fagard, 2005). Yet there is debate on the BP benefits of resistance training, as an association has been shown between vigorous resistance training and reduced arterial compliance (meaning the arteries stiffen, and do not expand as well to increased blood flow) (Miyachi et al., 2003). The reduction in arterial compliance can lead to an increase in systolic BP. However, it has also been shown that aerobic training performed in conjunction with resistance training negated the decrease in arterial compliance (Kawano et al., 2006). This suggests that resistance training be accompanied with aerobic training as a hypertension intervention strategy, which is in agreement with the American College of Sports Medicine recommendations for the prevention, treatment, and control of hypertension (Pescatello, Franklin et al., 2004). Aside from traditional aerobic and resistance exercise modalities, a recent Chinese study found that qigong (a series of relaxation, breathing, gentle movement, and walking exercises) also resulted in the reduction of both systolic and diastolic BP (Cheung et al., 2005). This is a notable finding that will hopefully lead to further research in alternative exercise methods that may be beneficial in reducing BP.
Is There an Additive Effect in Reducing Blood Pressure When Exercise is Combined with Weight Loss and Diet?
Overweight and obesity are associated with many cardiovascular risks including hypertension. Exercise has become a staple in weight management and weight loss programs, but is mostly effective when concurrently implemented with diet modifications. Specific dietary guidelines that have been shown to lower hypertension are explained in the Dietary Approaches to Stop Hypertension (DASH) diet, which recommends a diet rich in fruits, vegetables and low-fat diary foods as well as restrictions in alcohol and sodium intake (Bacon et al., 2004). A recent review of lifestyle interventions found that these guidelines as well as fish oil supplements resulted in significant reduction in BP (Dickinson et al., 2006). Although it has been suggested through other studies that potassium, magnesium, and calcium supplementation play a role in BP reduction, this review failed to find strong clinical support for these claims.
There remains controversy over the combined effort of exercise and weight reduction in reducing BP. Both have been shown to help independently, yet a comprehensive review by Hagberg and colleagues (2000) concluded from the gathered evidence that exercise training and dietary weight loss are independent, and that exercise can be effective in lowering BP without concomitant reductions in body weight. Other reviews maintain this idea but also reinforce the recommendation of the combination of diet and exercise as effective means to facilitate weight loss (Bacon et al. 2004). Therefore, if weight loss is desired in addition with BP pressure reductions, then diet should be modified accordingly.
Wait! Can Exercise Prevent Hypertension?
The encouragement of regular exercise is not only useful as a treatment method for individuals with hypertension, but should also be advocated as a means for prevention. Predictors that may be examined to evaluate the risk of developing hypertension include resting BP, family history, and physical activity levels. Higher physical activity levels have shown an inverse relationship to the development of hypertension. As well, Barengo and associates (2005) presented evidence that European men doing equatl to and greater than 4 hours per week of leisure-time physical activities (e.g. recreational sports, skiing, gymnastics, heavy gardening, hunting, fishing and walking/jogging) had reduced risk of hypertension. Thus physical activity and regular exercise can protect against hypertension.
What are the Acute and Chronic Anti-Hypertensive Effects of Exercise?
The responses to acute bouts of exercises are the physiological changes that occur within only a few exercise sessions, whereas the chronic adaptations are derived from the accumulation of several continuous exercise bouts over a period of time. The underlying mechanisms relating to anti-hypertensive benefits are not completely understood, however several studies have shown connections to specific physiological mechanisms. An immediate (acute) reduction in BP following exercise has been termed post-exercise hypotension and is agreed to be caused by reductions in vascular resistance (the resistance to flow that must be overcome to push blood through the circulatory system) (Hamer, 2006). The mechanisms associated with the chronic adaptations to blood pressure are more complex. A recent meta-analysis supports this chronic role being partially explained by a decreased systemic vascular resistance in which the autonomic nervous system and renin-angiotensin system (a hormone system that helps normalize long-term blood pressure and blood volume in the body) are most likely the underlying regulatory mechanisms (Cornelissen and Fagard, 2005a). Another factor contributing to this decrease in vascular resistance is the increase of nitric oxide production (from different sites in the body) causing a vasodilation (increase in the internal diameter of a blood vessel that results from relaxation of smooth muscle within the wall of the vessel) in response to regular aerobic exercise.
The rise in hypertensive patients causes concern and calls for action in the prevention and treatment for this condition. As hypertension is associated with an increase in risk for cardiovascular disease, it is vital that effective interventions are advocated to reduce overall morbidity and mortality. Although pharmacological treatments can be costly and necessary for treating some BP conditions, lifestyle modifications should also be implemented whenever possible. The role of exercise has been shown to be consequential in lowering both systolic and diastolic BP. Both aerobic and resistance training have been shown to facilitate anti-hypertensive responses, although aerobic exercise has been more largely studied. Specifics concerning optimal intensity and length of the exercise program are yet to be fully determined, however, moderate intensity exercise performed for at least 30 minutes on most days of the week still remains to be the minimal yet effective recommendation necessary for prevention and treatment of hypertension, as well as for promoting overall health.
Side Bar 1. Five Blood Pressure Training Tips To Use with Hypertensive Clients
1) Remember that many hypertensive clients may be taking medication (e.g. beta blockers and ACE inhibitors) that can alter the blood pressure response to exercise. Always know what medications your client is taking and how the drugs may affect the exercise training.
2) Allow for proper warm-up of clients to reduce the chance of a sharp and sudden rise in BP during activity.
3) Allow for an adequate cool-down to better transition the body to pre-exercise conditions, preventing dizziness, light-headedness and fainting.
4) Encourage clients to maintain normal breathing during exercise, especially during resistance training exertion to prevent the Valsalva effect (forced expiration with trachea closed) which causes a steep rise in BP.
5) When performing resistance training with clients who have hypertension, follow these guidelines from the American Heart Association (Pollock et al., 2000).
a. Single set of 8 to 10 different exercises (e.g. chest press, shoulder press, triceps extension, biceps curl, latissimus pull-down, lower back extension, abdominal crunch, leg press, leg curls and heel raise)
b. Perform 2-3 days per week
c. Repetition zone of 10 15 attaining moderate fatigue (Ratings of perceived exertion [RPE] of 12 to 13, or somewhat hard)
d. Progress very gradually and do not perform isometric exercises
Side Bar 2. Blood Pressure Measurement Recommendations to Follow
Although hypertensive clients should always be in contact with their physician to monitor blood pressure, you as a health professional should also periodically measure their blood pressure throughout the training. Here are six reminders on how to accurately measure blood pressure.
1) Allow your client to sit quietly in a chair with their legs uncrossed for at least 5 minutes prior to measurement.
2) Use an appropriate sized BP cuff. This is especially important for children, small adults and obese clients.
3) Make sure that the BP cuff is level with the clients heart. Rest the clients arm on a table or support the arm yourself. Do not let the client support his/her own arm.
4) Choose the right or left arm and stay with it. It is unclear if one side is better for measurement, but for consistency use the same arm for all repeat measurements.
5) Be aware of factors that may elevate blood pressure such as the use of caffeine, nicotine, or client anxiety.
6) Practice! Measuring blood pressure needs to be practiced to do accurately.
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Gavin C. Hillman has earned his Bachelors degree (Summa Cum Laude) in Exercise Science from the University of New Mexico (Albuquerque). He currently works as a personal trainer and fitness instructor and plans to earn a Doctorate degree in Physical Therapy.
Len Kravitz, Ph.D., is the Program Coordinator of Exercise Science and Researcher at the University of University of New Mexico where he recently won the "Outstanding Teacher of the Year" award. Len was honored with the 1999 Canadian Fitness Professional International Presenter of the Year and the 2006 Canadian Fitness Professional Specialty Presenter of the Year awards and chosen as the American Council on Exercise 2006 Fitness Educator of the Year.