March 17 (HealthDay News) -- National guidelines urge all Americans to engage in "moderate physical activity" at least 2.5 hours a week, but what does that mean if you're out for a stroll?

A new study provides the answer: It's equivalent to a brisk walk, or about 1,000 steps every 10 minutes.

"Now we know what moderate is," said the study's lead author, Simon J. Marshall, an assistant professor of exercise and nutritional sciences at San Diego State University. He suggests that people use pedometers to figure out if they're exercising at a high enough intensity.

The U.S. formerly recommended that people get 30 minutes of moderate exercise at least five days a week. But last fall, Marshall said, officials changed the guidelines to simply say that people should exercise 150 minutes a week.

"They dropped the per-day recommendation because there wasn't a compelling argument that people who exercised four days a week were any worse off than those who exercised five days a week," Marshall said.

For walkers, however, it was not quite clear what "moderate" activity meant, although some exercise specialists suggest that people walk 10,000 steps a day.

"Most people are familiar with the recommendation to get 30 minutes of exercise most days," said Dr. David Katz, director of the Prevention Research Center at Yale University School of Medicine. "Fewer people know that needs to be moderate intensity, and fewer still know what that means."

In the new study, researchers enlisted 58 women and 39 men, with an average age of 32, to walk on treadmills while a machine measured their energy expenditure. The idea was to determine what level of activity was in the moderate range.

The findings of the study, which was funded by the federal government, appear in the May issue of the American Journal of Preventive Medicine.

The researchers found that moderate exercise amounted to 92 to 102 steps a minute for men and 91 to 115 steps a minute for women.

"It's a bit like a brisk walk," Marshall said. "If you can imagine you're late for a bus, you're in a hurry. It's not a leisurely stroll, it's a brisk walk."

People may find it easiest to use a pedometer to measure their walking speed because it can be difficult to count steps and walk at the same time, Marshall said. "When you get above 50, you're trying to focus on what you're doing and where you're going."

There's one caveat though: The study found that about half of the pedometers on the market aren't accurate. Marshall said he would still recommend that people use them, however. Japanese-made models appear to be the most reliable when it comes to accuracy, he said.

The researchers said that three 1,000-step walks in a day, five days a week, would meet national exercise guidelines.

"Even walking below that threshold will usually have some benefit to your overall cardiovascular balance sheet," Marshall said. "But for reducing your risk of cardiovascular disease and other complications, the 30 minutes of moderate exercise seems to be important."

Katz said he suspects that some people will discover that they "need to take it up a notch."

"On the other hand, our advice has long been that 'moderate' is a pace that noticeably increases heart and breathing rate while still leaving you capable of speaking in full sentences," he said. "That is still about right. No pedometer required."

SOURCES: Simon J. Marshall, Ph.D., assistant professor, exercise and nutritional sciences, San Diego State University; and David Katz, M.D., M.P.H., director, Prevention Research Center, Yale University School of Medicine, New Haven, Conn.; May 2009, American Journal of Preventive Medicine