Is 30 Miles a Week or More too Much?

For people who exercise but fret that they really should be working out more, new studies may be soothing. The amount of exercise needed to improve health and longevity, this new science shows, is modest, and more is not necessarily better.

That is the message of the newest and perhaps most compelling of the studies, which was presented on Saturday at the annual meeting of the American College of Sports Medicine in San Francisco. For it, researchers at the University of South Carolina Arnold School of Public Health and other institutions combed through the health records of 52,656 American adults who'd undergone physicals between 1971 and 2002 as part of the Aerobics Center Longitudinal Study at the Cooper Institute in Dallas. Each participant completed physical testing and activity questionnaires and returned for at least one follow-up visit.

The researchers found that about 27 percent of the participants reported regularly running, although in wildly varying amounts and paces.

The scientists then checked death reports.