To read all the articles in the series, you can go to the mini-site: "Aging of Your Heart and Blood Vessels is Risky" by clicking here.

Introduction

A healthy endothelium, the inner lining of your blood vessels, is the key to maintaining strong blood vessels and preventing atherosclerosis. The four major components of a program to maintain endothelial wellness were discussed in the last Article of this Series, "You Can Prevent and Roll Back Atherosclerosis, and Decrease Your Risk for Heart Attack and Stroke".
These are shown in the figure below.

This article will discuss exercise in more detail. We know that exercise works in unison with diet, reduction of modifiable risk factors, and, at times, medication and dietary supplements, to reduce the risk for cardiovascular disease. But, how much and what type of activity is necessary to have an impact on this assemblage is often unclear. Many people believe that you need to run marathons for cardio-protection.

The specific benefits sought from an exercise program determine the level and type of exercise a person should perform. The goal for some is physical conditioning to the maximum achievable level. The targeted endpoint for most middle-aged to older persons is to prevent diseases like hypertension and atherosclerosis, which can lead to heart attack, stroke and heart failure. Others put emphasis on maintaining flexibility, increasing muscle strength, coordination, and balance to prevent frailty. Frailty was once considered the inevitable result of aging. In light of new research it is now proposed that frailty is a medical syndrome that may have a multisystem root, including inflammatory, hormonal and musculoskeletal bases. With this in mind, perhaps more emphasis needs to be placed on prevention plans, timely treatment of medical conditions, and exercise programs to prevent disability which can delay and often prevent frailty altogether.

Components of Exercise (Intensity, Duration and Frequency)

The components of an exercise plan include intensity (the difficulty of the exercise), duration (how long one performs the exercise), and frequency (how often the exercise is performed). Until recently, most of the information that has been accumulated regarding exercise has been related to sports and vigorous physical conditioning. Levels of physical conditioning have traditionally been measured by the amount of oxygen used by the body at peak exercise capacity. This is referred to as VO2max, which is measured during an exercise stress test done under professional supervision. (see Article #1, "Are You In Shape For Your Age?"). Changes in blood glucose and lipids are also altered with exercise and can be used to determine the response to changes in activity levels.

Physical conditioning can also be characterized by changes in body composition, such as an increase or decrease in body fat or an increase or decrease in muscle mass. These changes can be measured by techniques such as skinfold thickness measurement, underwater weighing (hydrodensitometry), body impedance technology and body imaging techniques (DEXA Scan, MRI). A future article will discuss body composition in more detail.

Dynamic (Aerobic) Versus Weight-Bearing Exercise

During dynamic aerobic exercise such as running, the body's oxygen consumption is increased in order to provide oxygen to highly working muscles. The oxygen is used in conjunction with burning of calories by muscles. This requires the heart and lungs to work hard during the exercise to circulate the required oxygen and remove waste products of muscle metabolism. Chronic aerobic exercise conditioning improves cardiac and lung function, and usually reduces body fat.

Weight-bearing exercise, however, is better than aerobic at building strength and muscle mass. Examples are weight lifting and isometrics, in which one part of the body is used to resist the movement of another. Weight-bearing or isometric exercise burns fewer calories than aerobic and is less beneficial for cardiovascular fitness. But weight-bearing exercise may be of great benefit in preventing frailty in older persons and still have some benefit to the heart and lungs, as increased muscle mass helps increase metabolism and often improves the ability to lose weight and maintain a healthy weight.

Effects of Intense Aerobic Exercise

Highly trained people - Master Athletes, for example - have made a commitment to habitual, regular, strenuous aerobic exercise, called endurance training. This exercise intensity increases VO2max by improving the ability of the heart and lungs to supply working muscles with oxygen, and enhancing the ability of muscles to burn oxygen. Exercise at this level produces major physiological changes in the heart. The heart chambers become larger allowing the heart to pump out substantially more blood per heartbeat. In contrast, the resting heart rate decreases.

To strengthen the heart and make these significant physiological changes, aerobic exercise must be performed at a reasonably high intensity. An endurance athlete exercises at a heart rate of 70% to 85% of his or her predictable maximum heart rate, which can be estimated as 220 minus the athlete's age. Exercise at this intensity is done for 30 to 60 minutes, at least 3 or 4 times a week, often more frequently if training is being done for a specific event.

What Intensity of Aerobic Exercise is Necessary to Promote Vascular and Heart Health?

One view on the intensity of exercise in people without evidence of heart disease is that only leisure exercise classified as heavy or vigorous is independently associated with reduced risk of premature death from heart disease. This perspective creates a dilemma for those whose want to improve their cardiovascular risk factors without committing to the intense exercise regimen of an endurance athlete. People who aren't highly motivated are likely to reject this level of involvement and avoid all exercise.

Fortunately, many population-wide studies have now concluded that physical activity of lesser intensity than endurance training does indeed provide many benefits, including living longer and decreasing the risk of incurring cardiovascular disease. This view maintains that all levels of exercise are good for you, even though more is considered better. An optimistic outlook on the benefits of moderate exercise has evolved because of these studies. Moderate amounts of exercise may help reduce body fat and thus reduce modifiable risk factors, such as diabetes and hypertension. The benefits may only be seen as slight alterations in risk factor indicators, such as blood pressure, LDL-cholesterol (the bad cholesterol), HDL-cholesterol (the good cholesterol), blood glucose level and insulin sensitivity, and thus are often not given the acknowledgment they deserve. (see Article #12, "Will You Have a Heart Attack as You Age? You Can Identify and Reduce Your Risk!").

Lack of due credit for moderate exercise is also due to the failure of conventional measurements of cardiovascular fitness, such as VO2max, to specifically report the beneficial aspects of moderate exercise on the individual's endothelial and vascular health. Measurements of vascular wellness, which help assess cardiovascular health and guide treatment, are only just emerging. Instruments for measurements of vascular stiffness and endothelial cell function, for example, are not readily available other than at research institutes at present.

Recent evidence also shows that absolute lack of exercise is a risk factor for heart disease. In light of this, any level of exercise should be applauded, since it has been proven that couch potatoes are at the highest risk for heart disease and premature death. People who exercise even moderately have been shown to decrease their risk factors for heart disease and to increase longevity.

Contradictory results from studies trying to determine what level of exercise is most beneficial suggest that exercise may have different effects in different populations. Men may respond different than women; and those with existing disease or at high risk may have a different response to exercise than those without disease or at low risk. Regardless, the evidence suggests that some physical activity for everyone is better than none, because even moderate exercise impart benefits to the endothelium (the inner lining of blood vessels), as shown in Article #15 of this Series, "You Can Prevent and Roll Back Atherosclerosis, and Decrease Your Risk for Heart Attack and Stroke".

How Do We Know That Moderate Exercise Has a Positive Effect on Endothelial Health?

Exercise has been shown to increase HDL-cholesterol and reduce the levels of total cholesterol and LDL-cholesterol, and to increase insulin sensitivity, which in turn reduces the risk of coronary artery disease, heart attack and stroke.

Evidence for the positive influence of exercise is also being found in a protein in the blood called C-reactive protein (CRP) that is part of the body's inflammatory response. Recall that Article #15,"You Can Prevent and Roll Back Atherosclerosis, and Decrease Your Risk for Heart Attack and Stroke", discussed how inflammation plays a role in hardening of the arteries. The body releases CRP as part of its response to infection and injury. Scientific studies have shown that persons with high levels of CRP appear to have a higher than average risk of cardiovascular disease. Increased CRP levels are believed to play a key role in the hardening and narrowing of arteries that can lead to heart attack and stroke. Chronic CRP elevations have also been linked to type 2 diabetes. Studies have shown that men who are the fittest tend to have the lowest levels of CRP in their bodies, while the least fit are more likely to show the highest levels of CRP. Those who are the most fit appear to be 83% less likely to have high CRP than the least fit. This inverse relationship between exercise level and CRP concentration remains even after other factors, such as age and obesity, are eliminated from the analysis. The most important information from these studies is that the greatest decrease in the risk associated with elevated CRP levels occurs between people who are the least fit and those who are only moderately fit, showing that it's important to get out of the lowest fitness group. As a measure of blood vessel inflammation, CRP levels in the blood are being recognized as a new way to measure an individual's risk of cardiovascular disease, and an innovative way to determine the benefit of exercise.

What is the Mechanism by Which Exercise May Reduce Inflammation in Blood Vessels and Keep Them Supple?

More research needs to be done to define the exact way physical activity reduces CRP levels and influences the inflammatory process. However, there is some insight as to how exercise influences the blood vessels. It's been shown that cells and chemicals linked with inflammation are found in miniature arterial blood clots. When you exercise the physical force of increased blood flow causes vascular cells to produce their own anti-inflammatory response.

In addition, the increased velocity of the blood during exercise causes an increase in shear stress on the vessel wall. Shear stress is the force that blood flow exerts on the endothelial cells that line blood vessels. High shear stress is protective, while low shear stress stimulates endothelial cells to manufacture proteins on their surface to trap fats and blood cells. These captured cells instigate the formation of miniature blood clots on the interior walls of the blood vessels, and begin the process of atherosclerosis. (see Article # 11, "The Inner Layer Of Your aging Blood Vessels Is A Battlefield.")
Greater velocity, which occurs during aerobic exercise, inhibits the production of these nasty sticky molecules and reduces the ability of plaque to form. Just as in a river or stream, the flow of blood tends to be more sluggish at branch points and areas of recirculation. Thus, dawdling flow, or low shear force, also irritates the blood vessel lining.

An additional effect of exercise is that the vessel walls are strengthened when they are forced to expand and contract with each heartbeat due to the increased velocity and blood volume.

Where Do You Go From Here?

When older people lose their ability to do things on their own, it doesn't just happen because they have aged. One of the major reasons is because they have become inactive. There have been a number of dubious studies on exercise intensity that have ended up confusing older persons, making it difficult for them to realize that moderate exercise far outweighs the risk of a sedentary lifestyle. This quandary, where even scientists can't agree, may make it guiltless for those not aspiring to do marathons or not able to engaging in strenuous training to sit in front of the TV, rather than to go for a brisk walk.

Older people who become sedentary lose ground in four areas that are important for staying healthy and independent. These are: endurance, strength, balance, and flexibility. Research has shown that exercise can maintain, or at least partly restore, these four areas. And, the exercise can be everyday physical activity, such as brisk walking. Small changes resulting from something as simple as a brisk walk every day can have a big impact on wellness. There is no need for a gym or expensive membership fees. Walking can be done without medicine balls or special equipment, except for good walking shoes.

The fact is that there are few health reasons that should keep older adults from increasing their physical activity. In the past persons with heart failure or those who had experienced a heart attack were encouraged by their physicians to decrease physical activity, when in fact that is exactly what they needed to be doing to prevent disability.

The next article in our series will help you get past the barriers that prevent older persons from engaging in physical activity. We will discuss in more detail walking as an aerobic exercise for heart health, in conjunction with weight-bearing exercise to maintain strength and flexibility.

Dr. Ed is a physician/scientist, who is internationally recognized for studies that range from humans to molecules on how the heart and blood vessels work in health and disease as the body ages.