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Exercise and Cardiovascular Disease

As noted in Chapter 1, CVD continues to be the number one cause of death in men and women in the United States. Although CVD is prevalent in all populations, a reduction in smoking and better medication for hypertension and cholesterol seemed to have reduced mortality numbers. Physical activity can also play a beneficial role in reducing the risk of CVD. Maybe the real question becomes not how to completely prevent CVD but, rather, how much physical activity is necessary to award the human body a protective effect against this common disease.

A cohort of 12,516 men from the Harvard Alumni Health Study reported 2135 cases of coronary heart disease (CHD). There was a significant inverse association with physical activity and risk of developing CHD. Those who expended less than 500 kcal/week showed the highest risk, and those expending between 1000 and 2999 kcal/week showed similar risk for CHD. A dose-response of physical activity was seen at the 1000-kcal/week level. The term dose-response refers to the level of the treatment needed to get a positive result. Here, it appears that getting at least 1000 kcal/week of physical activity was the dose needed to show a benefit. This study also reported a significant inverse association with vigorous activity, sport, and recreational activities and developing CHD.63

Swain and Franklin64 showed that the benefits from vigorous activity provided a significantly greater cardioprotective benefit than moderate exercise. They examined more than 500 scientific reports concerning exercise, physical activity, risk reduction, and cardiovascular changes and concluded that vigorous physical activity (> 6 MET) compared to moderate physical activity (3 to 5.9 MET) produced a more favorable risk profile. Vigorous physical activity at a level greater than 60% of the person’s aerobic capacity improved diastolic BP, glucose control, and aerobic capacity compared to moderate intensities. There was no difference between vigorous and moderate physical activity in terms of systolic BP (SBP), improvements in lipid profile, or body fat loss.64

Volume of Physical Activity

The total amount of time spent in physical activity is an important element of the guidelines. The combination of duration (time) and intensity is known as volume. The weekly volume needed to achieve health benefits results in a calorie expenditure of at least 1000 kcal. The Nurses’ Health Study included 72,488 women. At the 8-year follow-up, 645 nonfatal heart attacks or deaths were reported. Physical activity was calculated using MET-hours/week through a questionnaire. There was a strong inverse association between total energy expenditure and CHD risk. Women who had a significantly lower risk of CHD were physically active in equivalent to 3 hours of brisk walking each week or 1.5 hours of vigorous exercise each week.65

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Another study from the Women’s Health Study used a cohort of 38,987 disease-free women and followed them for a mean of 10.9 years. In that time, 948 cases of CHD were reported. The authors found that a normal-weight person showed no significant reduction in risk by expending 1000 kcal/week or more; however, there was a significant reduction in risk of CHD in women classified as overweight and obese. Both groups showed a significant reduction in risk of CHD by expending greater than 1000 kcal/week. Also, the data showed a dose-gradient increase in risk, starting with the women who were completely sedentary and ending with those who were active for more than 4 hours/week. The greatest or most significant reduction in risk could be seen between the groups who were active for more than 1 hour/week compared to the sedentary group and women who participated in less than 1 hour/week of physical activity. The risk reduction did not end there because it was shown that the walking speed also had a significant inverse trend in risk, with a faster walking pace having the lowest risk of developing CHD (Figure 2-3).66

Longer durations are not required for health benefits. The ACSM suggests that a minimum time of 10 minutes is effective as long as a total of 150 minutes is accumulated over a week. An article published in 1997 that used patients from the Multiple Risk Factor Intervention Trial reported that men in the least active (< 5 minutes/day) had a 22% higher CHD death rate than those who were only slightly more active. This study suggested that exercising longer than 20 minutes/day is associated with no additional reduction in the risk of dying from CHD.67

In a meta-analysis published in 2011, the researchers sought to validate the current guidelines for physical activity of 150 and 300 minutes/week for additional benefits. Although physical activity contains different levels of intensity and volume, the researchers focused their efforts on the duration of physical activity that best matched the current guidelines. Therefore, focusing on the duration recommended, the authors found 33 studies that met their initial criteria for inclusion. The risk reduction in all studies that measured leisure time physical activity showed a 26% reduction in CHD in those who were active compared to those who were sedentary. The individuals who met the minimum criteria of 150 minutes/week had a 14% decrease in risk of CHD compared to those with no activity, and those who received 300 minutes/week showed a

Figure 2-3. Relationship between walking pace and coronary heart disease. (Adapted from Weinstein AR, Sesso HD, Lee IM, et al. The joint effects of physical activity and body mass index on coronary heart disease risk in women. Arch Intern Med. 2008;168(8):884-890.) 20% decrease in CHD risk. The authors also showed that individuals who were active below the minimum guidelines still showed a significant decrease in risk compared to individuals who were inactive, supporting the notion that any physical activity is better than no physical activity.68 The DREW trial showed a significant increase in cardiovascular fitness (4.2%) in sedentary, overweight, postmenopausal women who performed 4 kcal/kg/week, equivalent to about 72 minutes/week of moderate physical activity.69

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