The usual advice to exercise a certain amount each week might not be the best for people with serious heart problems — they might need a different plan.

If you're at very high risk for heart problems, doing just 42 minutes of intense exercise a week seems to give you the best heart health boost — doing more might not help as much and could even reduce the benefits.

If you have insulin resistance, doing more than the recommended amount of exercise won’t help you live longer or avoid heart disease any better than sticking to the standard exercise guidelines.

If you're at high risk for heart problems, doing more than an hour of intense exercise a week might not help your heart as much as doing less — it could even be less beneficial.

People who exercise moderately—like jogging or cycling a few hours a week—have the lowest risk of heart attacks, but those who exercise way more than that don’t get any extra protection against heart events.

People who exercise a lot—like marathon runners or ultra-endurance athletes—tend to live longer than those who barely exercise, even though they don’t necessarily have fewer heart attacks.