Many doctors recommend moderate exercise to everyone from kids to the elderly. Federal exercise guidelines call for Americans to get at least 150 minutes per week of moderate exercise for optimal health.  Some studies have even suggested that moderate-intensity exercise, such as walking, may be just as beneficial as more vigorous exercise.

But what is the definition of moderate exercise? I’m sure many of you would like to know the answer, which is coming from a study led by Simon J. Marshall, an assistant professor of exercise and nutritional sciences at San Diego State University.

For the study, Marshall and his colleagues enlisted 58 women and 39 men , with an average age of 32, to walk on treadmills while a machine measured their energy expenditure. They wanted to determine what level of activity was in the moderate range.

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. 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,” Marshall said. “We believe that these data support a general recommendation of walking at more than 100 steps per minute on level terrain to meet the minimum of the moderate-intensity guideline,” he added.

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