How exercise protects and strengthens your heart (2)

How exercise protects your heart: 2

Aging is linked with dysfunction of the endothelium - the inner lining of the body's blood vessels, which plays a major role in maintaining a healthy circulation; exercise is known to improve endothelial function. So can exercise prevent age-related endothelial dysfunction and so protect older people from heart disease and other circulatory problems? That is the question an Italian research team set out to answer with a study comparing young and elderly sedentary people with young and elderly athletes.

The study population comprised four groups: 12 healthy sedentary subjects under 30; 12 healthy sedentary subjects over 60; 11 young athletes and 14 elderly athletes. Apart from age, the four groups were comparable for sex distribution, blood pressure, body mass index and levels of glucose and cholesterol in the blood. Predictably, however, the athletes had lower resting heart rates, higher V02 max values and better blood cholesterol profiles than the sedentary subjects.

The researchers carried out a series of complicated experiments designed to assess the reactivity of circulation in the forearm to two chemical stimulants: acetylcholine, which works via the endothelium, and sodium nitroprusside, which works independently of the endothelium. They were working on the theory that regular physical activity would be shown to improve endothelium-dependent blood flow by maintaining availability of the relaxing factor nitric oxide (NO). Their key findings were as follows:

* The vasodilating (blood vessel-widening) effect of acetylcholine was similar in both the young groups, but the elderly athletes showed a greater response than their sedentary counterparts;
* The vasodilating effect of sodium nitroprusside was also similar in both young sub-groups. In the elderly groups the response was slightly and non-significantly reduced, with no difference between athletes and sedentary subjects;
* Elderly athletes were much more responsive than their sedentary controls to infusion of a vasoconstricting (blood vessel-narrowing) chemical called L-NMMA.

'Taken together, these results demonstrate that sedentary elderly subjects are characterised by the presence of age-related endothelial dysfunction caused by oxidative stress-induced reduction in NO availability,' report the researchers. 'In these clinical conditions, long-term physical training appears to reverse this alteration.

Most puzzling and unexpected was the finding that endothelial function in young age groups is not apparently improved by physical training. There are two possible explanations for this: first, it may be that in young people nitric oxide production may work at a maximum rate which cannot be further increased; secondly circulatory improvements may be limited to the trained areas - eg the legs. Why, then, were the elderly athletes' blood vessels more responsive than those of the sedentary counterparts? Perhaps, suggest the researchers, 'because of the presence of a more pronounced endothelial dysfunction'.

They conclude that: 'The beneficial effect of exercise is related to preservation of NO availability by a mechanism probably linked to the prevention of oxidative stress and the consequent NO breakdown. This beneficial effect could be important in accounting for the positive impact of regular exercise on cardiovascular risk in the elderly population.'

Circulation 2000; 101:2896-2901

Isabel Walker

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Tagged in Exercise & Physiology
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