L

Sedentary Low Moderate High

Activity/fitness level

Figure 2 Summary of the results from six studies in which fitness level was determined (three studies) or activity level assessed by questionnaire (three studies) in individual populations. Follow-up was generally between 7 and 9years except in Sandvik's study, which had a 16-year follow-up. The 'low level' group for each study represented in this figure was the activity/fitness level next to the least active/fit group. The 'high level' represents the group that was the most active/fit for the particular study. If the study participants were grouped by quintile, the 'moderate' group is the average of the third and fourth quintiles. (From Killoran AJ, Fentem P, and Caspersen C (eds.) (1994) Moving On. International Perspectives on Promoting Physical Activity. London: Health Education Authority, with permission.)

information, and subsequent mortality was assessed over an 8-year period. In men who were initially sedentary but started participating in moderately vigorous sports (intensity of 4.5 METS or greater), there was a 41% reduced risk of CHD compared to those who remained sedentary. This reduction was comparable to that experienced by men who stopped smoking. The second study examined changes in physical fitness and their effects on mortality. In this study of 9777 men, two clinical examinations (including treadmill tests of aerobic fitness) were administered approximately 5 years apart, with a mean follow-up of 5.1 years after the second examination to assess mortality. Results showed that men who improved their fitness (by moving out of the least fit quintile) reduced their aged-adjusted CHD mortality by 52% compared with their peers who remained unfit. Furthermore, such changes in fitness proved to be the most effective in reducing all-cause mortality when compared with changes in other health risk factors (Figure 3).

Mechanisms of Effect

Exercise appears to reduce the risk of CHD through both direct and indirect mechanisms. Regularly performed physical activity may reduce the vulnerability of the myocardium to fatal ventricular arrhythmia and reduce myocardial oxygen requirements. Aerobic training also increases coronary vascular transport capacity via structural adaptations and altered control of vascular resistance. Risk of thrombus formation may also be reduced with regular exercise through its effects on blood clotting and fibrinolytic mechanisms. Regular endurance exercise may also improve the serum lipid profile (particularly in favor of an enhanced HDL: total cholesterol ratio) and have beneficial effects on adipose tissue lipolysis and distribution. Regular exercise may also reduce postprandial lipemia, increase glucose transport into muscle cells, and improve the elasticity of arteries.

Exercise Prescription

For protection against CHD and other diseases associated with inactivty, exercise needs to be habitual, predominantly aerobic in nature, and current. Evidence from work carried out on British civil servants suggests that to be cardioprotective, exercise should be moderately vigorous (>7.5kcalmin-1 (>31.4kJmin-1) or 6 METS, equivalent to walking at approximately 3 miles per hour up a gradient of 1 in 20) and performed at least twice weekly. However, other studies have indicated that lower intensity activity is also effective as long as the total accumulated exercise energy expenditure is greater than approximately 2000 kcal week-1 (>8368 kJ week-1).

Thus, recommendations from the U.S. Surgeon General suggest that everyone older than the age of 2 years should accumulate 30 minutes or more of at least moderate-intensity physical activity on most— preferably all—days of the week. Such activity may embrace everyday tasks such as stair climbing and walking, recreational physical activities, and more

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