Exercise

The greater coronary heart disease morbidity of sedentary as opposed to physically active workers was demonstrated many years ago by J N Morris and his colleagues in a comparison of London bus drivers and conductors. These two groups of transport workers belonged to the same social class and had similar lifestyles. They differed principally in the amount of physical activity in which they engaged when at work. The drivers were confined to a small enclosed driving compartment which rendered them almost completely immobile, whilst the conductors were continuously active, especially as they constantly had to run up and down the stairs of the doubledecker London buses. During the five-year follow-up the drivers had a CHD incidence almost double that of the conductors. The differences between the two groups became greater as their members grew older (Table IX.1).' The finding of this untoward accompaniment of physical inactivity has been confirmed by the results of the Framingham study2 and a 27 cohort based rigorous meta-analysis reported by Jesse Berlin and Graham Colditz. These authors found a relative risk of death from coronary heart disease of 1.9 (CL 1.6-2.2) for sedentary as opposed to high physical activity groups, and the benefits were shown to be greater in the studies that the authors judged to be methodologically stronger.3 Conversely, in the Whitehall study of British civil servants leisure-time physical activity has been found to have cardiovascular health benefits similar to those apparently conferred on the London bus conductors by their workaday exertions. Vigorous weekend exercise apparently protected the middle-aged men from fatal heart attacks and non-fatal first episodes of coronary heart disease.4 It is probable that a randomized and controlled prospective study of the cardiovascular consequences of prolonged inactivity will never be undertaken. It would be both unethical and impractical to enforce a long-term sedentary lifestyle on a control group. However, the physiological means by which regular exercise has cardioprotective effects are now well defined. Animal studies have shown that the coronary arterial capacity becomes greater relative to the cardiac muscle mass and an increase in coronary artery diameter has been demonstrated angiographically. Capillary growth is induced and increase in coronary blood flow in response to need