International Task Force for Prevention of
Coronary Heart Disease

CORONARY HEART DISEASE: REDUCING THE RISK

3.3 Physical exercise

Lack of exercise is a source of high CHD risk, and this relationship is independent of other risk factors. There is strong epidemiological evidence that aerobic physical activity reduces the risk of CHD, with a dose-response relation that holds up to several hours of exercise per week. Thus moderately active men who habitually spend 2000-3000 kcals per week in exercise have 2-3-fold fewer coronary events than those spending less than 500 kcal per week. For example, a man of average body weight will spend about 300 kcals during a half hour of jogging at 9 km per hour. Some energy expenditure can be attained during the activities of daily life, e.g. using the stairs instead of the lift, walking or cycling instead of driving small distances etc.. Those who exercise regularly have less body fat, higher HDL-cholesterol, lower LDL-cholesterol and triglyceride levels, greater insulin sensitivity and lower blood glucose and blood pressure, and often feel better.

An exercise programme should be recommended to all subjects in sedentary occupations, with a clear and detailed prescription to meet the parallel needs of safety, personal enjoyment and effectiveness. Doctors need to know the basic requirements of such a programme.

Aerobic exercise is obtained using large muscle groups to perform a high number of repetitive movements against relatively low resistance, for example walking, which is an excellent form of aerobic activity. Others are jogging, cycling, swimming, calisthenics e.g. 'aerobic classes', and rowing. Patient preference is important, not least in order to maximise compliance.Typically, a programme comprises three phases. Warming up for 5 to 10 minutes by stretching and other gentle activity is followed by an endurance or aerobic phase of 20 minutes or longer according to fitness, and finally by a cool-down period of progressively decreasing vigour that permits cardiovascular responses and heat production to subside gradually.

In persons who have been sedentary in recent months, in those with known cardiovascular disease or at high risk, and in persons aged more than 40 years, the initial duration and intensity of the endurance phase should be suitably reduced. Ten minutes of gentle activity such as walking may be an appropriate first step, increasing at intervals of one week or longer according to tolerance, as fitness increases. Increments are first achieved by increasing duration. Later intensity is increased, for example by walking briskly, or by alternate walking and jogging.

Dosage is affected by duration, intensity and frequency of exercise. The preferred frequency is 4-5 times weekly with an endurance phase of 20 - 30 minutes when a more gentle programme is chosen, or (in young fit persons) 3 times weekly with an endurance phase of 40 up to 60 minutes if it is more vigorous. While the latter option is suitable for younger persons and for fit middle-aged and older persons, a lesser duration and moderate intensity are appropriate to most middle-aged and older people, e.g. walking, fast walking, or alternate walking and jogging, or gentle swimming for 30 minutes at least 4-5 times weekly. Many authorities regard it as acceptable to divide moderate exercise such as walking into shorter aerobic periods of 10-15 minutes, 2-3 times a day, if the person finds this more acceptable.

Intensity can be judged subjectively, or objectively by instructing the subject to monitor pulse rate during exercise. A training effect is obtained at rates of 60% of maximum rate for age, and this is the initial target rate (Table 7). With increasing fitness, in persons at low cardiovascular risk, the target may be increased gradually to 75% of maximum, for example by increasing the speed of walking.

Table 7: Appropriate pulse rate during aerobic exercise.

To judge a suitable level of exercise subjectively, the person is instructed to aim for a comfortable intensity of activity, sufficient to extend her/him slightly. Mild shortness of breath during exercise should abate within four minutes or less of resting. These target rates are not applicable to patients taking beta blockers and other cardioactive drugs. Lower target rates are set, at least initially, in patients with CHD or at high risk of myocardial infarction. Fitness is best gauged by subjective feeling and heart rate recovery times after exercise. The individual should be aware of untoward effects that require reporting to the instructor or physician: delayed recovery time (longer than 5 minutes), chest pain, syncope or persistent coughing.

Supervised exercise is unnecessary for persons at low cardiovascular risk, but is recommended for those at higher risk e.g. patients with overt cardiovascular disease, especially during the initial weeks at least. Such persons at higher risk, and those aged 35 years and over who have been sedentary, should undergo formal exercise ECG testing prior to selection of a programme of exercise. Other examples of patients at high risk are those with angina or silent ischaemia, high grade ventricular arrhythmias, low ejection fraction, hypotension on exercise, and inappropriate tachycardia during exercise: for such patients, initial ECG monitoring during exercise is preferable. Exercise programmes must also take into account disabilities from respiratory or muscuto-skeletal disease, and peripheral vascular disease.