This is an excerpt from Physical Activity and Health Guidelines by Riva Rahl.
Currently more than 50 million Americans—and more than 50% of the American population over the age of 60—have hypertension, or high blood pressure (Hagberg 2005). Worldwide, the number of people with hypertension is estimated to be 1 billion! Furthermore, because blood pressure tends to increase with age, the number of people with hypertension is likely to rise significantly as the U.S. population continues to age. Unfortunately, due to a lack of symptoms a large number of individuals are unaware that they have the silent killer, as hypertension is called, and do not realize their hypertension is placing them at a higher risk for a heart attack or stroke. Although hypertension affects nearly every organ, its lack of symptoms means that many individuals do not realize the damage that may be occurring even at modest elevations of blood pressure.
Physical activity is considered one of the mainstays in the nonpharmacological treatment of hypertension. This chapter discusses the current definition of hypertension and introduces the physiological relationship between exercise and blood pressure, as well as provides some background and mechanistic details. Then it presents both nationally and internationally issued activity guidelines for individuals with hypertension. Also, because of the close and causal relationship between hypertension and CAD, this chapter also includes guidelines that pertain to CAD.
Benefits of Exercise for Hypertension
The definition of hypertension has changed over time. Currently, the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7: NHBPEP 2003) defines normal blood pressure as a pressure less than 120/80 mmHg (see table 10.1). Elevated blood pressure, which at one time was diagnosed only when in excess of 160/100 mmHg, is a primary cardiac risk factor and also increases the risk for stroke, type 2 diabetes, kidney disease, and vascular disease. According to the JNC 7, the risk of CVD begins at only 115/75 mmHg and doubles with each incremental increase of 20/10 mmHg. People who are classified as prehyper-tensive have twice the risk of developing hypertension. Even individuals with normal blood pressure have a high lifetime risk of developing hypertension—an estimated 90% risk for individuals with normal blood pressure at age 55 (Vasan and others 2002)!
For people with prehypertension, exercise is one of the primary recommended lifestyle changes that can lower blood pressure to a normal level. In fact, even in individuals who have a normal blood pressure, regular aerobic exercise may lower resting blood pressure, although the extent of lowering is less than that seen in individuals with frank hypertension. In the JNC 7, physical activity compares favorably with the other recommended lifestyle changes when it comes to reducing resting blood pressure—table 10.2 gives examples of these changes and their relative effects. Also, physical activity may contribute to weight loss, which can reduce blood pressure even further.
So, although the distensibility or pliability of blood vessels decreases with age and makes hypertension more likely, hypertension is not necessarily an unavoidable consequence of aging, because regular physical activity is clearly effective in preventing hypertension and reducing its intensity. A single session of aerobic exercise creates a sustained hypotensive response that lasts up to 24 h (Hagberg and others 2000), and over time participation in regular physical activity can have long-term benefits. Postulated mechanisms for the reduction of both systolic and diastolic blood pressure that occurs with regular exercise training include the following:
- Reduced visceral fat
- Improved sodium elimination due to altered renal function
- Reduced plasma renin and catecholamine activity
- Reduced sympathetic and increased parasympathetic tone
Because physical activity decreases hypertension, it also reduces the potential contribution of hypertension to cardiovascular risk. In addition to lowering blood pressure, physical activity generally causes a regression of left ventricular hypertrophy, improves lipid profiles, and lowers the risk for type 2 diabetes. This combination of risk reduction has a substantial long-term benefit on cardiovascular risk. There are also notable benefits to other health parameters. Individuals with hypertension may not necessarily achieve normal blood pressure through exercise, but they will likely see improvements in lean body mass, glycemic control, and inflammatory biomarkers.
Overall, a regular physical activity program lowers both systolic and diastolic blood pressure. However, during aerobic exercise, the normal physiological response is a gradually rising systolic blood pressure with a stable or slightly decreasing diastolic blood pressure. In addition, during resistance training and particularly during high-intensity efforts, blood pressure may rise significantly. These natural responses to exercise necessitate guidelines for people with hypertension so that they may receive the benefits of activity safely without increasing their risk for injury or disease.
The use of antihypertensive medications also necessitates physical activity guidelines. Exercise is recommended as an adjunct to antihypertensive medication as there appears to be an additive effect of physical activity with most antihypertensive medications. Beta-blockers, however, may interfere with the antihypertensive effect of exercise (Ades and others 1988). For hypertensive individuals who regularly participate in physical activity, beta-blockers also blunt the peak heart rate and blood pressure; the former effect requires using an alternative to target heart rate for measuring exercise intensity.