Even short bursts of exercise can reduce Americans' risk of disease and death, study says

Do the national exercise guidelines need a change? That’s a question raised by a new study by researchers at the National Cancer Institute and the National Institutes of Health.

Americans are bombarded with mixed messages: Exercise only counts if you do it this way or that way, or for a short time or a long time. Confused, some seem to be willing to sit down on the couch and wait till all the recommendations are straightened out. But with the benefits of exercise so important to health, this study hopes to bring some clarity and reassure people that some is better than none -- and that it is linked to curtailing premature death.

"Virtually all [studies] report that higher volume of [moderate or vigorous physical activity, MVPA], whether performed intermittently or in sustained bouts, lowers all-cause mortality," wrote Deborah Rohm Young and William L. Haskell in an editorial accompanying research published in the Journal of the American Heart Association.

The old benchmark of 150 minutes per week of moderate activity (or 75 minutes of vigorous activity) originated in 1995. The “rules”: Each time you exercise, it should be for at least 10 minutes.

"For about 30 years, guidelines have suggested that moderate-to-vigorous activity could provide health benefits, but only if you sustained the activity for 10 minutes or more," an author of the research, William E. Kraus, M.D., of the Duke University School of Medicine, said in a press release. "That flies in the face of public health recommendations, like taking the stairs instead of the elevator, and parking farther from your destination. Those don't take 10 minutes, so why were they recommended?"

The new study finds that the length of each bout or episode of exercise is unrelated to the benefit seen in living longer. Five minutes of jogging, researchers said, “counts” toward better health.

The study used information from accelerometers, like those found in cellphones and FitBit watches, which can measure certain types of motion. Researchers utilized the ActiGraph AM-7164 and corresponding information from the National Center for Health Statistics and the National Health and Nutrition Examination Survey of 2003 to 2006.

To be counted in the study, the people wearing the ActiGraph had to wear it at least one day, for at least 10 hours, up to a maximum of a week. Researchers followed almost 5,000 people over the age of 40 for more than six years. They considered the people in two groups: Those who had bouts of exercise approximately five minutes in length, and those whose exercise lasted more than 10 minutes.

Getting about 60 minutes per day of moderate-to-vigorous physical activity cut the risk of death over the time period by half, while getting about 100 minutes per day cut the risk to approximately 75 percent -- and it was the total time moving, not the length of exercise that mattered.

Those exercising at the highest rate were rare. Young and Haskell cautioned that "the majority of our sample did not accumulate any [moderate-to-vigorous physical activity] in bouts of 10 minutes with [the higher] threshold." The analysis cites “unpublished findings” that they claim bolster their argument.

The editorial warns that this study didn’t discriminate between intentional exercise sets (going for a brisk walk) and unintentional physical activity (walking around the house doing chores, or walking up a flight of stairs).

For that, Young and Haskell said, what’s needed is a study that asks people to deliberately perform exercise of short, medium and lengthy "bouts" and track their health.

"Experimental studies are needed ... [and] would provide necessary information that would be required to change national physical activity guidelines on [moderate-to-vigorous physical activity] bout lengths," they said in the editorial.

Dr. John Byun is a radiation oncology resident based at the Rutgers Cancer Institute of New Jersey and a resident in the ABC News Medical Unit.