Exercise and Why It’s Important for Heart Attack Prevention

Exercise is a prevention strategy as well as a treatment. According to the Centers of Disease Control (CDC) statistics, more than 64 percent of the U.S. adult population is overweight, and roughly 31 percent of American adults are obese. That translates to approximately 59 million American adults that are obese. Incidence of adult obesity has increased sharply since the 1970s. In 2001, the CDC estimated that more than 300,000 deaths per year were associated with overweight and obesity. In adulthood, obesity becomes a serious health issue. Heart disease and cancer, the leading killers of Americans, often have a strong correlation with obesity.
Adult obesity is caused by:

• unhealthy eating habits established in childhood, adolescence, and late teens that continue in adulthood.
• a sedentary lifestyle coupled with a decreased metabolic rate.
• lifestyle changes due to the proliferation of labor-saving technology, such as elevators, cars, dishwashers, televisions, power lawn mowers, and computers.
• a decrease in metabolic needs and energy expenditure coupled with the same or increased food intake.

Diabetes, which is often associated with obesity, is also increasing sharply in the United States. Type 2 diabetes affects more than 16 million, or almost 8 percent, of American adults. An estimated 34 percent of this population has impaired fasting glucose levels, 15 percent have impaired glucose tolerance, and 40 percent have one or both. Diabetes increases the risk of developing CAD by up to seven times in women and up to three times in men. Physical activity may slow the onset and escalation of type 2 diabetes and its complications while also improving body weight and a host of other factors, such as insulin sensitivity, glycemic control, blood pressure, lipid profile, fibrinolysis, endothelial function, and inflammatory defense systems. Lack of exercise is risk factor that can be modified and have a positive impact on obesity, type 2 diabetes, and CAD—although how much, how often, and how long to exercise for optimal benefit continue to be debated (Bassuk and Manson 2005).

Exercise Intensity
We measure exercise intensity by kilocalories burned per minute (kcal/min), or in a unit called the metabolic equivalent (MET). A MET is the ratio of metabolic rate during exercise to metabolic rate at rest. Moderate-intensity exercise, such as brisk walking, burns 3.5–7 kcal/min (3–6 METs), and vigorous exercise, such as running, burns 7 kcal/min or more (6+ METs).

An earlier belief that exercise must be vigorous in order to be helpful, and performed for at least twenty minutes, three times per week, evolved into a recommendation that adults engage in thirty minutes of moderate-intensity physical activity most days, preferably every day (Pate et al. 1995). These earlier guidelines were modified in 1995 by the CDC and the American College of Sports Medicine, followed in 2002 by the Institute of Medicine (IOM), which doubled the daily moderate-intensity activity goal to sixty minutes on the belief that half an hour isn’t enough for maintaining a healthy weight or achieving the greatest health benefits (Dietary Reference Intakes for Energy, Carbohydrates, Fiber, Fat, Protein, and Amino Acids 2002).

The Harvard Alumni Health Study demonstrates that more is indeed better. This study evaluated exercise patterns in approximately thirteen thousand qualifying alumni (males without CAD) over approximately fifteen years to learn what level of exercise contributes most significantly to the prevention of heart disease. The study determined that burning more calories is correlated with increased longevity. There was no apparent association between engaging in light activities and mortality rates, whereas increased moderate activity showed a trend toward lower mortality rates, and greater energy expended in vigorous activities definitely predicted lower mortality rates. People who did not exercise or were overweight had a shortened lifespan (Lee and Paffenbarger 2000).

Although exercise lessens the effects of many chronic diseases, 25 percent of adults in the United States do not participate in any physical activity, and 60 percent are not physically active or do not participate in a regular exercise regimen.

Changes in individual risk factors with physical activity don’t completely account for the benefit seen with exercise. According to a 2007 study, lipids decreased 5 percent, blood pressure decreased 3 to 5 points, and 90-day blood sugar was 1 percent less in response to exercise. This contrasts with the large reductions—30 percent to 50 percent—in heart attack and stroke risk (Mora et al. 2007). So there must be more to it.

What Doesn’t Kill You Makes You Stronger
Regular strenuous exercise protects against heart attacks but produces oxidative stress and inflammation as well. How could this be helpful? The reason is that inflammation caused by exercise is different from inflammation associated with disease states. Physical activity lowers the risk of a heart attack by increasing anti-inflammatory molecules (Kasapis and Thompson 2005).

This is the body’s adaptation to the inflammation caused by exercise, with the net result of less inflammation. Research has proved that higher levels of physical activity are associated with lower levels of inflammatory markers. In one study, inflammatory markers were lower in joggers and aerobic dancers (higher impact) than in cyclists and weight lifters (lower impact). In another study, CRP levels were lowest among middle-aged men who engaged in high levels of strenuous aerobic exercise compared with those who rarely exercised (Futterman and Lemberg 2006).

The inflammation caused by strenuous exercise triggers an increase in inflammatory activity in the body. Most people adapt to these changes, but in some people they can trigger acute cardiac events and blood clots (Siegel et al. 2001). This explains why some older adults drop dead while exercising or experience deep vein thrombosis. The only way to learn if you are one of those people who don’t adapt to exercise-induced inflammation is to measure these inflammatory markers in the blood. Some of the inflammatory molecules include immune system cytokines and CRP.
Elevated levels of proinflammatory molecules are usually balanced by a cascade of anti-inflammatory molecules. Despite the elevated levels of proinflammatory molecules that peak during strenuous exercise, such as in marathons, researchers have noticed only a modest increase in CRP levels in most habitual exercisers. This indicates that the inflammation triggered by strenuous exercise is not followed by a full-blown response (Futterman and Lemberg 2006).

A review published in 2006 looked at the effect that moderate versus vigorous exercise had on lowering heart attack risk. Vigorous activity (greater than or equal to 60 percent aerobic capacity) was more effective for lowering diastolic blood pressure, blood sugar, and for increasing fitness, but exercise intensity had no significant improvement in systolic blood pressure, lipid profile, or body fat loss beyond the benefits seen with easy to moderate exercise. The review concluded that exercise performed at a vigorous intensity generally gives more cardioprotective benefits (Swain and Franklin 2006).

You Decide How Much Benefit You Want from Exercise
1. Easy to moderate aerobic exercise: lowering of systolic blood pressure, improved lipids, improved body composition (e.g., less fat, more muscle). Example: walking, easy jogging, easy bicycling, hiking, easy rowing, stair stepper, elliptical machine, etc.
2. Moderate to vigorous exercise: lowering of systolic and diastolic blood pressure, improved lipids, improved body composition, improved blood sugar control, increased cardiorespiratory fitness, reductions of risk for all causes of mortality (cancer, stroke, heart attack, etc.). Example: hiking uphill, running, cross-country skiing, cycling, rowing, and swimming.

How Much Exercise to Prevent a Heart Attack?
As stated above, the most physically active people live longer and have less total cardiovascular disease, heart attacks, and atherosclerosis. Research also indicates that more vigorous exercise is better than moderate exercise, but physical activity need not be vigorous to provide health benefits. As discussed above, moderate activity is associated with significant reductions in CAD. I often recommend adding some intensity to the workouts as well as resistance training and flexibility exercises. In this way you gain the benefits of both intensity and moderation. I believe that exercise plans should be tailored to individual preferences. My point here is to drive home the fact that exercise is mandatory if you want to live a long, healthy life.

Regarding marathon running, there is some debate as to the protective benefits (Mohlenkamp et al. 2008). In one study when 108 healthy male runners over fifty years of age were compared to age-matched nonrunners, there was no difference in coronary plaque burden. Adding concern was the finding that running in more marathons was associated with subclinical myocardial damage. There are also published cases of male runners with advanced CAD. This finding should stress the importance of getting a heart scan if you are a male runner or athletic person over thirty-five years old. Exercising at a high intensity could put you at increased risk of a coronary event if there is a moderate to high level of plaque or if you have exercise-induced hypertension. Some people’s hearts also enlarge in a maladaptive way that can also be bad news. There is an unfounded belief that exercise can make one immune to heart attack and stroke. I have a hard time convincing older athletes in Boulder, Colorado, to undergo screening because they believe that they are immune to heart disease. I like all my patients to get a stress echocardiogram and a heart scan by age forty.

In case you’re confused, let me summarize: While the minimal effective amount of exercise is unclear, we can say that some is better than none, and more appears to be better than a little. Also, if you are not exercising now, just doing the bare minimum will give you a good return on investment.

Basic Exercise Prescription

1. Nonexerciser (“exercise hater”): thirty minutes of brisk walking (or equivalent, such as treadmill or stationary bike), five days a week. Weights are optional.
2. Nonexerciser (“I don’t enjoy exercise, but I’ll do it”): thirty minutes initially, building up to sixty minutes of brisk walking (or equivalent), three days a week; one day of vigorous exercise for twenty minutes, with ten minutes of aerobic warm-up and ten minutes of aerobic cool down; two thirty-minute sessions of strength training per week with a trainer at the gym.[1] Vigorous (hard) exercise should be 80 percent of your maximum heart rate (220 – age = maximum heart rate × 80 percent). An example for a forty-six-year-old with 80 percent of your maximum heart rate would be: 220 – 46 = 174 × 0.8 = 139.2 beats per minute.
3. Exerciser: sixty minutes of moderate-intensity aerobic exercise with intensity sessions at ladder intervals (one minute hard, one minute rest; two minutes hard, two minutes rest, and so on), longer intervals with equal rest (eight minutes hard, eight minutes rest times three). Typically, intensity sessions are done once or twice a week. I also like to incorporate a slow long-distance session of two to three hours. This session is easy. You should be able to carry on a conversation without difficulty. Moderate exercise means you can talk and carry on a conversation but have to breathe hard in between sentences. During hard efforts, such as intervals, you can still speak but it is difficult to say more than very short sentences. Using this model, it’s easy to gauge your effort without heart-rate monitors and other gadgets.

Key Points and Action Steps Regarding Exercise

• Strenuous exercise may cause a short-term inflammatory response. Conversely, exercise training and regular physical activity are anti-inflammatory, reduce hs-CRP levels, improve endothelial function, and even boost growth hormone and sex hormone levels. All reduce the risks of atherosclerosis in the coronary, cerebral, peripheral vascular, and renal arteries.
• More exercise is better than a little, but some is better than none.
• Exercise plans should be tailored to the individual.

 

[1] It’s important to learn proper technique so that you do not cause injury. Two sessions for four to six weeks with a trainer should be adequate.