Why is 90 minutes of exercise per week the ideal amount?

Walking as little as 10 minutes a day can make a tremendous difference for your heart health. See more heart health pictures.
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It may seem like an oversimplification to say that exercise can prevent a heart attack. There are so many factors involved -- genetics, arterial damage from high blood pressure, and clogged arteries all play into it. The shocking thing is that it's not oversimplified. In the vast majority of people, getting regular exercise can dramatically lower the risk of heart disease, the risk of heart attack even after the arteries are clogged, and the risk of a second heart attack. The laundry list of heart-disease symptoms that respond to exercise includes blood pressure, circulation, stress, weight and cholesterol levels.

While the need for exercise is cut-and-dried, the question of how much you need is far hazier. Experts are constantly changing it up. First you need 30 minutes three times a week. Then you need 60 minutes every day. The fact is, there's no way most of us are going to get an hour a day, seven days a week. Most of us aren't even up for 20 minutes of huffing and puffing.

But you don't need to run a marathon to benefit your heart. Studies show that even minimal exercise, as little of 10 minutes of walking each day, can do great things. In 2007, researchers at Louisiana State University found that overweight women who started exercising -- just walking at a relaxed pace -- about 70 minutes a week increased their hearts' oxygen consumption by more than 4 percent [source: Washington Post]. Oxygen consumption is a sign of your heart's health.

That's definitely the low end, though. The more time you spend exercising, the greater the benefits. In that same study, the women who exercised about 30 minutes a day increased their heart's oxygen consumption by more than 8 percent.

So how much exercise do you really need in order to see significant heart benefits? And should you be running, lifting weights or doing yoga? In this article, we'll sort through the mixed signals and see which types of exercise will help your heart the most and how much time you should spend at it.