Regular, moderate-intensity exercise has many health benefits, including a reduction in the risk of chronic diseases such as hypertension, diabetes and coronary artery disease.

In absolute terms, the risk of sudden death is low - one death occurs for every 396,000 man-hours of jogging. Another study estimated that one sudden death occurs annually for every 15,240 previously healthy joggers. For high-school and college students, the incidence of exercise-related death is only one in 133,000 males and one in 769,000 females.

While the risk of sudden death appears to be transiently raised during vigorous exercise compared to at rest, the risk of this happening is far higher in sedentary than in regularly active individuals. For instance, the overall risk of cardiac arrest in men who are habitually active is only 40 per cent of that for sedentary men.

Hence, the overall benefits of regular exercise outweigh the transient increase in risk. In sedentary individuals, the risk of sudden death increases 56-fold during vigorous exercise, whereas the increase is only five-fold for active individuals.

In cases of sudden death, there is usually an underlying, previously undiagnosed heart or brain abnormality - exercise serves only as a trigger. These abnormalities vary between age groups, with coronary artery disease predominating in people older than 35 while congenital abnormalities of the heart account for the majority (but still rare) of the younger cases. One such condition, hypertrophic obstructive cardiomyopathy, occurs in only two out of every 1,000 births.

It is important to bear in mind that there is no evidence to suggest that exercise can injure an otherwise-healthy heart.

Many of these hidden conditions can be picked up through pre-participation screening. Those with known risk factors (e.g., hypertension, diabetes, smoking) as well as those with symptoms such as chest discomfort, dizziness and shortness of breath should especially undergo screening.

Dr Jason Chia
President
Sports Medicine Association of Singapore