How much you exercise may be more important than how hard you exercise in terms of heart health, according to a study of sedentary overweight men and women. And, many will be happy to hear, exhaustive amounts of exercise are not needed for heart health.

In journal CHEST, researchers from North Carolina report that people who walk briskly for 12 miles per week or for about 125 to 200 minutes per week will significantly improve their aerobic fitness and lower their risk of developing heart disease.

"Anything beyond walking briskly for 12 miles per week, whether increasing your intensity or the amount of miles, has additional benefits," Brian D. Duscha from Duke University Medical Center in Durham who was involved in the research said. "So there is a separate and combined effect."

He also emphasized that the 12-miles-per-week walkers in the study improved their fitness without losing any weight. "People need to know: even without losing weight, you are getting significant benefits by exercising -- you're improving your fitness level, decreasing fat and increasing muscle and improving your lipid panel -- so don't stop exercising," Duscha said.

"The other thing to realize is that people gain 3 to 4 pounds a year, so exercise is really important for weight maintenance," Duscha said.

There is a clear link between heart health and fitness. However, less is known on how the amount and intensity of exercise relates to increases in fitness for individuals at risk for heart disease.

To better understand the effects of different amounts of exercise on aerobic fitness, Duscha and colleagues randomly assigned 133 overweight sedentary men and women showing signs of rising cholesterol levels to 7 to 9 months of no exercise; low amount/moderate intensity exercise (the 12-miles per week walkers); low amount/vigorous intensity (12 miles of jogging per week); or high amount/vigorous intensity (20 miles of jogging per week).

The study subjects did not alter their diet during the study.

After completing their exercise assignment, all of exercisers had improvements in peak oxygen consumption and time to exhaustion -- two established markers of fitness - compared with levels at the beginning of the study.

Interestingly, however, the vigorous intensity exercisers did not get any "fitter" than the moderate intensity exercisers. "The moderate intensity group only exercised to 40 or 50 percent of their max," Duscha explained. "That's walking briskly up a hill or walking fast -- you could walk around the neighborhood after dinner and get that in. You don't have to go jog, climb on the stairmaster or elliptical trainer and kill yourself."

However, increasing the amount of exercise from 12 to 20 miles per week -- at the same intensity -- provides even more cardiovascular benefits.

"Therefore," Duscha and colleagues conclude, "it is appropriate to recommend mild exercise to improve fitness and reduce cardiovascular risk, yet encourage higher intensities and amounts for additional benefits."

SOURCE: Chest, October, 2005.