If you’re habitually sedentary, your risk of heart attack or stroke doubles. And only 21.7 percent of Americans meet the government’s physical fitness guidelines.

In fact, studies have shown that the majority of adults spend most of their time sitting. Since 1950, sedentary jobs have increased 83 percent. Physically active jobs now make up less than 20 percent of the U.S. workforce, down from roughly half of jobs in 1960.

If you’re one of those people whose job involves a long day sitting, it’s important that you break up the day with short periods of activity called “exercise snacks.”

As readers know, I recommend walking at least one hour a day. Not only will this build up endurance, but your body also creates a collateral blood supply that could save your life if you have a heart attack.

But sometimes you don’t have an hour to devote to walking. What can you do then?

Previous studies have shown that brief bouts of vigorous exercise called high-intensity interval training (HIIT) are effective when performed with a few minutes of recovery time between the intense bursts. Such training may require a total time commitment of just 10 minutes or so.

For one study, researchers at McMaster University in Ontario set out to determine whether exercise snacks such as vigorous stair climbing could improve a person’s cardiorespiratory fitness — an important health marker that is linked to longevity and cardiovascular disease risk. They found that the group who performed such bursts of exercise regularly not only improved their endurance, but their strength as well.

I do want to add a warning about vigorous exercise, however. This study involved healthy young people. But if you’re between the ages of 45 and 65, you need to be careful about sudden exertion and always consult your doctor before getting involved in a vigorous exercise program.

Still, the general principle holds. A short period of moderate activity — like a brisk walk, a short bike ride, or even dancing — will boost your overall fitness level.