Exercise has been shown to help prevent heart attacks (JAMA Intern Med, 2015 Jun;175(6):959–67), and a new study suggests that you can gain protection with as little as 150 minutes of moderate exercise per week, or 75 minutes per week of more vigorous activity. Pushing yourself to exercise at high intensity for many long hours did not appear to provide additional protection from heart attacks. The Master@Heart study, presented at the recent American College of Cardiology (ACC) Scientific Session/World Congress of Cardiology and written up in the European Heart Journal (March 6, 2023), found that:
• middle-aged competitive endurance athletes had more plaques in their heart arteries than similarly fit and healthy exercisers with a healthy lifestyle who did not compete
• the competitive endurance athletes had the type of plaques that appear to be just as unstable as those found in non-competitive exercisers

This agrees with several other studies that show that competitive endurance athletes have more plaques in their heart arteries than healthy non-exercisers (Circulation 2017;136:138–148). However, previous studies have shown that the plaques in competitive endurance athletes are far more stable and therefore far less likely to break off to cause a heart attack (Circulation 2017;136:138–148). See Stable Plaques: Why Exercisers Have Fewer Heart Attacks? Competitive endurance athletes are at very low risk for heart attacks and dying of heart disease, much lower risk than that of healthy non-exercisers, but the authors note that some endurance athletes can develop heart abnormalities from exercising too much.

Details of the Study
The study evaluated heart artery plaques in:
• 191 life-long competitive master endurance athletes
• 191 athletes who started in sports competition after age 30
• 176 healthy non-competitive exercisers who engaged in no more than three hours a week of exercise.

All participants were male, average age of 55, with a low risk for heart attacks. All three groups had similar weight, blood pressure, blood cholesterol, and HBA1c tests for diabetes. The life-long athletes had higher maximal ability to take in and use oxygen. Both athletic groups had lower body fat percentage (15 percent) than the non-competitive exercisers (19 percent).

Endurance Athletes Have More Stable Plaques
Other studies show that endurance athletes have more stable plaques that are less likely to break off and cause a heart attack. The MARC-2 study followed 291 older men for 6.3 years with a test called Coronary Artery Calcification (CAC), and found that the amount of calcium in the arteries leading to the heart increased most in men who exercised at the highest intensity, even more than those who exercised the most time (Circulation, January 4, 2023). The authors said this showed that intense exercise increases the amount of plaques in arteries, which may be true. However, they would then have to explain why intense exercisers are far less likely to suffer heart attacks than non-exercisers (JAMA Cardiol, 2019;4(2):174-181). Exercise is prescribed both to treat and to prevent heart attacks (Front Cardiovasc Med, Feb 3, 2021;8:753672).
• CAC measures only the size of plaques. It does not measure obstruction of blood flow to the heart. As plaques form, the involved arteries usually widen to accommodate the plaques (JAMA Cardiol, October 27, 2021).
• Intense exercise increases the amount of calcium in plaques (Circulation, January 4, 2023). Calcium in plaques stabilizes them to help prevent plaques from breaking off, which is the cause of most heart attacks.

My Recommendations
Heart attacks have little to do with arteries being narrowed by plaques. A heart attack usually is caused by a sudden immediate complete blockage of blood flow to the heart muscle itself. First a plaque breaks off from the inner lining of an artery leading to the heart. This is followed by bleeding and clotting. Then the clot extends to block all flow of blood through that artery to deprive the heart muscle completely of oxygen, so that part of the heart muscle dies. Exercise helps to prevent heart attacks, and it appears that you may gain the protection if you follow the most recent physical activity guidelines, which recommend 150-300 minutes of moderate exercise (such as brisk walking) per week, or 75-150 minutes per week of vigorous activity (such as running).

Caution: Exercise can cause a heart attack in a person who has blocked arteries or heart damage. Check with your doctor before you start a new exercise program or increase the intensity of your existing program.