Baffled or annoyed by the federal government's 30-minutes-per-day-of-moderate-exercise-five-days-per-week dictum? A new study suggests that clearing a lower bar offers significant health benefits.

As little as 12 miles of brisk walking per week yields meaningful aerobic fitness gains and reduces risk of cardiovascular disease in at-risk populations.

The study examined 133 overweight men and women, aged 40 to 65, all of whom were sedentary before the study and had high cholesterol. Researchers randomly assigned them to one of four groups: walking 12 miles per week at 40 to 55 percent of VO2 max (a key measure of cardiovascular fitness, roughly the fastest pace each could sustain for about a minute); jogging 12 miles per week at 65 to 80 percent of peak VO2; jogging 20 miles a week at 65 to 80 percent of VO2 max; and a control group that was told not to exercise throughout the nine-month study.

Lead study author Brian Duscha, an exercise physiologist at the Duke University Medical Center's division of cardiology, says the results are the first to specify a minimum exercise level for achieving significant aerobic conditioning gains, and should appeal to aspiring exercisers looking for an accessible, understandable target.

"For some people, the government recommendation is overwhelming and [as a result] they do nothing. We scientifically showed that you get benefit at 12 miles a week" at an intensity lower than most people would assume is needed to show gains.

Walkers in the study sustained the oft-cited "brisk" pace (Duscha: "more than a stroll ... but at a pace you can maintain for 30 or 40 minutes"), covering about three miles in about an hour, three or four times per week.

(Those are ballpark calculations based on some complex data. The details: The 12-mile walkers averaged 203 total minutes per week and 3.6 walks. The 12-mile joggers averaged three runs a week of about 42 minutes each. The 20-mile joggers averaged 3.7 sessions weekly at about 53 minutes per run.)

The 12-mile walkers showed absolute VO2 max gains of about 6 percent in the study; the 12-mile joggers improved by more than 10 percent; and the 20-mile joggers gained about 16 percent. Time-to-exhaustion measurements showed similar escalating benefits.

People in all three exercise groups lost weight -- an average of about three pounds -- but there was no significant difference in pounds dropped among the three groups.

More meaningful, Duscha says, is the fact that even those who did not lose weight showed aerobic fitness gains. "That is huge. People stop exercising when they don't lose weight. This study says, `You will still gain a lot of benefit even in the absence of weight loss.'"

People ready to step up their exercise regimens could increase either workout time or intensity, Duscha says. "The research showed that [boosting] either helps. ... But knowing Americans, I would never urge people to increase their time commitment."

Source: Diabetes In Control: Chest, Oct, 2005, a publication of the American College of Chest Physicians.