Your heart's risk during a hard workout is tiny, and regulars carry even less

Regular physical activity is associated with better quality of life and lower cardiovascular illness and all-cause mortality, and the more people do, the greater the benefit. Yet there is a paradox at the heart of that story: during a bout of exercise and in the minutes after it, the risk of an adverse cardiovascular event or sudden cardiac death temporarily rises above what would be expected at rest. That paradox frightens people, especially when a death during a race or a gym session makes the news. This review set out to quantify how likely such events really are in apparently healthy adults, and what can be done to prevent them.

The authors performed a systematic review of the published literature using electronic databases, then added relevant articles picked by hand from reference lists and other sources. They examined the likelihood of adverse cardiovascular events during and immediately after physical activity of varying types and intensities in apparently healthy adults. They also reviewed strategies for preventing those events, and set the acute risk against the long-term reduction in risk that regular activity confers, so the two could be weighed against each other rather than considered in isolation.

The incidence of adverse cardiovascular events in adults was extremely low during and immediately after physical activity of all types and intensities. The risk of sudden cardiac death and of nonfatal events remained well below 0.01 per 10,000 participant hours. People with long-standing exercise experience carried significantly lower risk than those without it. Increasing age and higher exercise intensity were both associated with greater risk. In most cases of exercise-related sudden cardiac death, hidden cardiovascular disease was present, and the death itself was typically the first clinical sign that anything was wrong.

The review confirms what the dose-response evidence on activity and mortality has long suggested: the transient rise in risk during a session is dwarfed by the protection regular exercise builds over time. It also sharpens the real problem, which is not exercise itself but the occult structural heart disease and inheritable conditions that make lethal rhythm disturbances possible during exertion. Identifying those hidden conditions before they announce themselves remains, in the authors' words, a key challenge. How best to screen for them in apparently healthy people is the open question this field has yet to settle.

For a healthy person who trains, this is a reason to stop worrying that a hard session is gambling with your heart: the absolute risk during and after exercise is extremely small, and it is smaller still in people who have been active for a long time. It is also worth knowing that risk rises with age and with intensity, and that when tragedies do happen they almost always involve heart disease nobody knew was there. The finding that experience protects is itself informative: consistency appears to be part of what makes vigorous exercise safe.