Explained: The ‘U-shaped’ relationship between exercise and heart attack risk

Is ‘more exercise’ associated with better health benefits?

Studies examining epidemiology and biological plausibility support the idea that being more active or having better cardiorespiratory fitness can lower the risk of coronary heart disease. Moreover, exercise is known to slow down aging, which is why many people believe that “more exercise is better. “Due to this, a lot more people around the world are doing endurance training, competitive long-distance endurance events, and high-intensity interval training,” pointed out Dr Ranjan Modi, senior consultant and head of interventional cardiology, Sarvodaya Hospital, Sector-8, Faridabad.

Dr Mehta clarified that this paradox is seen only with high-volume, high-intensity exercise over extended periods. “Long-term exercise-induced stress can in some individuals result in cardiac maladaptation such as left ventricular hypertrophy, increased coronary artery calcification, the release of cardiac biomarkers, myocardial fibrosis, exercise-induced arrhythmic remodeling and atrial fibrillation,” said Dr Mehta.

However, Dr Modi said that intense physical exercise, especially when done by people who aren’t fit, can greatly raise the risk of sudden cardiac death and acute myocardial infarction in people who are already at a high risk. “Recent research has also shown that high levels of exercise and doing a lot of it can change the heart in bad ways. These changes can happen quickly in the coronary arteries, cause biomarkers to be released in the heart during exercise, cause myocardial scarring, and cause rhythm disturbances (Atrial fibrillation). A dose-response curve in the shape of a U or reverse J often shows the connection between these unhealthy responses and physical exercise,” described Dr Modi.

Exercise is crucial (Source: Getty Images/Thinkstock)

Aerobic exercise at a moderate level for at least 150 minutes a week or intense aerobic exercise for at least 75 minutes a week can lower the risk of death by a large margin. “Intense physical exercise done over a long period can be bad for the heart and may make it less resistant to early death and heart disease,” cautioned Dr Modi.

The link between exercise intensity and the risk of rhythm disturbances (atrial fibrillation or AF) is also shaped like a U. “People who are sedentary or do a lot of vigorous activity daily are most likely to get AF. Instead of going all out, it might be better to aim for modest efforts or to rest from hard exercise at least once a week,” said Dr Modi.

Despite that, physical activity should be encouraged in all individuals, including those with chronic cardiac disease, as there are multiple benefits even from moderate exercise, said Dr Prashant Pawar, consultant, interventional cardiology, Fortis Hiranandani Hospital, Vashi. “Veteran athletes show a higher prevalence of atrial fibrillation compared with sedentary individuals of similar age. However, athletes appear to live longer than those who have a sedentary lifestyle,” said Dr Pawar, highlighting that perhaps we should be prepared to accept that too much of a good thing, in the form of chronic intense exercise, may foster “abnormal changes” in a previously normal heart.

DISCLAIMER: This article is based on information from the public domain and/or the experts we spoke to. Always consult your health practitioner before starting any routine.