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Hypertension and exercise

American Fitness, March-April, 2003 by Erika Zanabria, Gregory L. Welch

Hypertension or high blood pressure, a common disease in industrial societies, has reached epidemic proportions. Approximately 50 million Americans are hypertensive and, though it can affect anyone, the greatest incidence occurs among middle-aged and older individuals. In addition, generally more men than women and African Americans than Caucasians have hypertension (ACSM, 1993). Results from epidemiologic studies have associated low levels of physical fitness with hypertension, independent of body mass or obesity (Lesniak and Dubbert, 2001). Often referred to as the silent killer, hypertension is a leading risk factor for stroke, myocardial infarction, chronic heart and renal failure (Stewart, 2000).

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Defining Hypertension

Hypertension is defined as blood pressure equal to or greater than 140/90mmHg. Thus, hypertension can result from either increased systolic pressure (the first number of the two values), diastolic pressure (the second number) or both. An increase in either raises the risk of medical complications, thus the higher the increase, the greater the risk (Haskell, 2001). Individuals with a blood pressure reading over 160/95mmHg have a 150 to 300 percent higher annual incidence rate of coronary artery disease (CAD), chronic heart failure, intermittent claudication and stroke than individuals with normal blood pressure (ACSM, 1993).

Hypertension is generally classified into one of two categories: essential and secondary. Although the cause of essential hypertension is unknown, it is believed to develop in individuals with certain hereditary variations in genes. In contrast, secondary hypertension is a consequence of a known etiology (i.e., disease process), thus results from another disease (e.g., renal artery stenosis, coarctation of the aorta, adrenocortical or benign tumors and hypokalemia) (ACSM, 1997).

Blood Pressure Response

Blood pressure (i.e., the force exerted by blood against the arterial walls) is indirectly measured with a sphygmomanometer or blood pressure cuff. Blood pressure is determined by how much blood the heart pumps and the resistance to blood flow. Systolic pressure (SBP) is produced as the heart ejects blood during ventricular systole. Diastolic pressure (DBP) is created during ventricular relaxation (i.e., the period in which the ventricles fill with blood) (Powers and Howley, 1996). A normal blood pressure reading for a person at rest is 120/80mmHg for males and 110/70mmHg for females.

Dynamic exercise (which consists of alternating muscle contraction and relaxation, such as in walking, running and cycling) produces a different blood pressure response than static or resistance exercise (in which the muscle contraction is held for more than a few seconds before relaxing, such as in strength training and isometric exercise). During dynamic exercise the systolic rate should rise steadily as exercise intensity increases, while the diastolic rate should vary minimally. Consequently, a single session of dynamic exercise usually evokes a normal rise in SBP from baseline levels in a hypertensive unmedicated person. During vigorous dynamic exercise, a typical systolic rate range is between 160mmHg and 220mmHg. However, if the systolic rate becomes greater than 240mmHg, does not increase as exercise intensity increases and/or drops below resting levels, then the cardiovascular system is not responding appropriately and the exercise bout should be stopped. The same should be done if the diastolic rate increases 20mmHg above resting value or reaches 115mmHg (Haskell, 2001).

On the other hand, during static or heavy resistance exercise, the pressure within the muscle increases and causes the small blood vessels (i.e., arterioles and capillaries) in it to collapse. Whenever this occurs, oxygen rich blood cannot reach the working muscle. This hypoxia (i.e., lack of oxygen) rapidly increases SBP and DBP during the contraction. The increased blood pressure is believed to be the body's attempt to send oxygen to the working muscles by forcing open the arterioles (Haskell, 2001). The speed and magnitude of the rise in systolic and diastolic rates are greater as the contraction intensity and duration increase. However, this can be avoided if the contraction lasts only a few seconds or there is a rest period of a few seconds before the muscle contracts again. Additionally, exercisers should avoid Valsalva's maneuver (i.e., holding their breaths during the exertion phase of an exercise). This maneuver reduces blood flow to the heart, thus decreases the amount of blood the heart pumps and potentially limits blood flow to the brain. A good lifting technique is to exhale on the exertion (i.e., lifting) phase and inhale upon the relaxation phase.

Medication

Although antihypertensive drugs reduce blood pressure, some may also dampen exercise performance. Hypertension control through beta-blockers and, to a lesser degree, the calcium antagonists diltiazem and verapamil, reduces the heart rate response to sub-maximal exercise. Beta-blockers blunt exercise-mediated increases in heart rate and cardiac output (Q) and may reduce exercise performance. This reaction is more pronounced with non-selective beta-blockers (e.g., propranolol). Conversely, dihydropyridine (i.e., derivative calcium antagonists) and direct vasodilators may increase heart rate response to sub-maximal exercise (ACSM, 1996). Vasodilators, alpha-adrenergic blocking drugs and calcium channel blockers do not suppress cardiac output or exercise capacity.

Hypertension and exercise

American Fitness, March-April, 2003 by Erika Zanabria, Gregory L. Welch

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