Can exercise be a bad thing? Though trained marathon runners are not immune to fatal heart attacks, sudden death during or soon after strenuous  51  on the squash court or on the army training ground is not unheard of. But no one knows just how common these sudden deaths linked to exercise are. The registration and investigation of such cases is very patchy; only a national survey could determine the true  52  of such deaths in sports. But the climate of medical opinion is shifting  53  exercise, for the person recovering from a heart attack as well as the  54  lazy individual. Training can help the victim of a heart attack by lowering the  55  of the oxygen the heart needs at any given level of work so the patient can do more before reaching the point where chest pains indicate a heart  56  of oxygen. The question is, should middle-aged people, in particular, be screened for signs of heart disease before taking up vigorous exercise?

Most cases of sudden death in sport are caused by lethal arrhythmias in the beating of the heart, often in people with undiagnosed coronary heart disease. In North America anyone over 35 is advised to have a physical  57  and even an exercise electrocardiogram (ECG). The British, on the whole, think all this testing is unnecessary. Not many people die from exercise,  58 , and ECGs are not notoriously inaccurate. However, two medical cardiologists at the Victoria Infirmary in Glasgow, advocate screening by exercise ECG for people over 40, or young people already at risk of  59  coronary heart disease. Individuals showing a particular abnormality in their ECGs have, they say, a 10 to 20 times greater risk of  60  developing signs of coronary heart disease, or of sudden death.