More than 7.5 million Canadians and 50 million Americans have been diagnosed as having high blood pressure, or hypertension. Over many years, hypertension is a major cause of strokes, heart attacks, congestive heart failure and kidney failure. Also, recent data indicates that having even moderately elevated blood pressure, over time, increases the risk of dementia in old age. Unlike other potentially deadly diseases, hypertension, often called the "silent killer," frequently has few outward symptoms, but even more interesting is that exercise directly affects, and is affected by, this all-too-common disease.
Resting Blood PressureFor blood to flow from the heart and lungs throughout the body, it needs to be under pressure. Each time the heart beats, it sends blood all over the body through the circulatory system. As the heart contracts, the pressure in the arteries increases; as the heart relaxes between beats, the blood pressure decreases.
Therefore when blood pressure is measured, there are two values: a higher, or systolic blood pressure and a lower, or diastolic one. A healthy blood pressure for a person at rest is at or below 120/ 80 millimeters of mercury (mm Hg).
Note: To accurately determine resting blood pressure, measure it always after sitting quietly. If it is high, measure it again at least twice on different days.
Hypertension can be due to an increase of either the systolic or diastolic pressure, or both. An increase in either raises the risk of medical complications, and the higher the increase, the greater the risk.
Blood Pressure Responses During ExerciseBlood pressure responds differently to dynamic exercises, which consist of alternating muscle contraction and relaxation, such as walking, running and cycling, than to static or resistance exercise where the muscle contraction is held for more than a few seconds before relaxing, such as strength training and isometric exercise.
Dynamic exercise: During dynamic exercise, the systolic rate should rise steadily as the intensity of the exercise increases, while the diastolic rate should change very little. For example, in a healthy person performing vigorous exercise, his or her blood pressure might jump from 120/80 at rest to 190/75 at the most intense part of the exercise.
The increase in the systolic rate during dynamic exercise depends on a person's resting level blood pressure, the intensity of the activity and other personal characteristics. A typical range for the systolic rate during vigorous dynamic exercise is 160 to 220.
During dynamic exercise, if the systolic rate becomes greater than 240, doesn't increase as the intensity of the exercise increases, or drops below resting level, then the cardiovascular system is not responding appropriately and the exercise should be stopped.
Nearly opposite of the systolic rate, the diastolic rate typically does not change much during exercise. If the diastolic rate increases by 20 above the resting value, or reaches 120, the exercise should be stopped.
Static or heavy resistance exercise: When an exercise causes a muscle to use more than about 25 percent of its strength, such as during heavy weight lifting, the pressure within the muscle increases and causes the small blood vessels (arterioles and capillaries) in the muscle to collapse. When this happens, oxygen-rich blood cannot reach the muscle. Reducing the amount of blood flowing to the working muscle during static or heavy resistance exercise can cause temporary pain in the muscle.
This lack of oxygen, called tissue hypoxia, causes a rapid increase in both systolic rate and the diastolic rate throughout the contraction. It is believed that this increase in blood pressure is the body's attempt to get oxygen to the working muscles by forcing open the arterioles.
The speed and magnitude of the rise in the systolic and diastolic rates are greater as the intensity of the contraction increases and as the duration of the contraction lengthens. This does not happen, however, if the contraction lasts for only a few seconds or if there is a rest period of at least a few seconds before the muscle is contracted again.
The higher blood pressure rapidly increases the workload on the heart and can cause an inadequate amount of blood to flow to the heart muscle (myocardial ischemia) in patients with coronary artery disease. Also, the very high blood pressure reached during vigorous sustained muscle contractions could cause a stroke or the splitting of the aortic wall (where there currently is a weakness) in patients already at risk.
Exercisers should be careful to avoid holding their breaths during the contraction phase of the exercise. Called a "valsalva maneuver," holding the breath during a sustained muscle contraction reduces blood flowing back to the heart, resulting in a decreased amount of blood the heart has to pump and potentially limiting the quantity of blood flowing to the brain. Exercisers should remember to exhale on the exertion (or lifting) phase and inhale upon the relaxation (or lowering) phase.
Research shows that physically active men and women have lower average blood pressures and are diagnosed less frequently with hypertension than their sedentary counterparts. The minimum amount of activity associated with lower blood pressure appears to be 30 to 60 minutes per day at a moderate intensity level plus a gradual warm-up and cooldown.
Exercise training studies in people with high-normal blood pressure or "borderline hypertension" (see Table 1) have shown that performing moderate-intensity cardiovascular exercise for 45 minutes per day at least three times per week causes a reduction in blood pressure at rest and during moderate exercise. Examples of exercise include brisk walking, jogging, gardening and housework.
People with established hypertension should use exercise in conjunction with other forms of treatment, including antihypertensive medication, and should avoid sustained heavy resistance or isometric exercise and highly competitive situations involving vigorous exercise. Also, those with hypertension are prone to sudden drops in blood pressure following exercise. This can cause fainting, so gradual cooldowns are very important.
Note that some blood pressure lowering medications, especially beta-blockers, can substantially reduce heart rate at all levels of exercise. Thus, the usual method of using a person's heart rate for setting exercise training intensity is not appropriate for these exercisers; perceived exertion should be substituted instead.
Also, resistance training is not recommended as a primary form of exercise for people with hypertension, as it has not consistently been shown to lower blood pressure. It is acceptable to be used as part of an overall workout program including cardiovascular exercise, but not solely on its own.
Treating High Blood PressurePeople with high blood pressure must be under the care of a physician and often need to take medications. Reductions in blood pressure can help prevent a stroke, heart attack, heart failure and kidney failure.
In the United States and Canada, an increase in blood pressure typically occurs as people age. This elevation is not caused by age itself, however, but instead by what typically goes along with age, such as additional body weight (most of it fat), decreased daily physical activity, high intake of salt or animal products and stress. To help prevent hypertension, note the following recommendations:
- Know your blood pressure - the higher it is, the more frequently it needs to be checked
- Avoid becoming overweight, or lose weight if your body measurement index (BMI) is greater than 25
- Perform moderate physical activity 30 to 60 minutes five days a week or more
- Limit alcohol intake to no more than two drinks per day
- Restrict sodium intake (table salt)
- Increase dietary potassium and calcium intake
- Move toward a plant-based diet and reduce consumption of animal products (meat, cheese, eggs)
- Develop skills to deal with stressful situations
Although hypertension affects millions of people, it is preventable and treatable. Knowing how exercise affects, and is affected by, blood pressure can be important in the prevention and treatment of this common disease.
The National High Blood Pressure Education Program has established the following classification for blood pressure in adults:
Table 1. Classification of Resting Blood Pressure (in mm of mercury) Category Systolic Pressure Diastolic Pressure Optimal less than 120 less than 80 Normal less than130 less than 85 High-normal 130-139 85-89 Hypertension Stage 1 140-159 90-99 Stage 2 160-179 100-109 Stage 3 180 or higher 110 or higher # # # William Haskell, Ph.D., is a professor at Stanford University specializing in exercise and cardiac risk factors and a member of the Life Fitness Academy Scientific and Medical Advisory Board. This article was sponsored by Life Fitness.
