Nevertheless, there are still plenty of reasons to avoid too much sedentary “screen time,” Dr. Ulf Ekelund of the MRC Epidemiology Unit in Cambridge, UK and colleagues say, given potential negatives including “violence and aggressive behavior, poor academic performance, and poor body image.”

To help tease out the role of time spent in different types of activity in making children fat, independent of screen time and otherwise being a couch potato, Ekelund and his team looked at 1,862 children 9 to 10 years old, 23 percent of whom were overweight or obese.

Using a wristwatch-like device to measure the amount and intensity of activity children got throughout the day, the researchers looked for associations between this activity and children’s waist size, amount of body fat, and body mass index (BMI). Kids also reported how much time they spent watching TV or using a computer.

Sixty-nine percent of the children were getting at least an hour of moderate physical activity a day, while 58 percent reported having less than two hours of screen time daily.

While children who spent more time not moving had bigger waists and a larger percentage of body fat, much of this relationship could be attributed to the fact that they spent less time engaging in moderate physical activity.

But the time children spent engaging in vigorous activity, and their combined moderate activity-vigorous activity time, had the strongest ties to waist circumference and fat mass.

For instance, every 6.5 minutes a child spent doing vigorous activity like playing ball, bicycling, or running around outside was associated with a 1.32-centimeter reduction in waist size, the researchers found. But 13.6 minutes of moderate physical activity only reduced waist size by half a centimeter.

Based on the findings, the researchers say, children should still be encouraged to limit their sedentary time, but this alone won’t be enough to tackle childhood obesity.

“Interventions may therefore need to incorporate higher intensity-based activities to curb the growing obesity epidemic,” they conclude.

Boys in the study got an average of a half-hour of vigorous activity each day, while girls got 22 minutes. “There is no clear cut answer” as to how much vigorous activity is optimal, Ekelund noted in an email to Reuters Health.

“For most health outcomes, the more activity you do the better.” But, he added, people who do lots of strenuous activity may still put on too much weight if they take in too many calories.

It is now recommended that adults should do at least 2.5 hours a week of moderately intense physical activity such as brisk walking, or 1 hour and 15 minutes of vigorously intense jogging, swimming laps or other aerobic activities. A combination of the two types of exercise many bring about the same results, but the exercise must be in sessions that are at least 10 minutes long to raise the heart beat enough to provide benefits.

Adults should also do muscle strengthening exercise two or more days a week. The exercise should work all major muscle groups. Free weights, resistance machines, push-ups, pull-ups, carrying heavy loads, or heavy gardening will all provide the same results, better muscle control and body tone.

Combining strength exercises with 5 or more hours of moderate intensity or 2.5 hours vigorous intensity aerobic exercise will provide even more health benefits. Older Americans should follow the guidelines for other adults, if they are able.

If their balance or physical abilities are in someway compromised they should do as much as they can. There are exercises for specific conditions, such as improving balance. Adults with disabilities are also encouraged to follow the guidelines as much as possible.

Children and adolescents should do an hour or more of moderate to vigorous aerobic activity each day. Vigorous activities are advised at least three days a week, and bone strengthening exercise such as running, or rope jumping should be included. Sit-ups, push-ups, and climbing trees, are among muscle strengthening activities that could be included in the exercise programs.

Healthy pregnant women should have a minimum of 150 minutes of moderate aerobic activity weekly, both during and after pregnancy. Usually any activities which a woman was doing prior to becoming pregnant can be continued during the pregnancy, but that should be checked out with the health care provider.

The new guidelines allow an individual to find activities to match their schedule, whether it is an elliptical stepper, walking the course when playing golf, or walking the dog and providing exercise for man and beast.

Individuals who need to lose weight or to keep off weight they have previously lost may need to increase the amount of activity to accomplish those goals. With more than 60 million obese adults in this country and at least one third of the children overweight and 16 percent already considered obese the necessity for action is now.

HHS wanted science behind the how much to exercise question. A panel of experts reviewed the data to provide the answer. Besides the duration of the exercise periods, the panel reiterated what was already known, regular physical activity cuts the risk of heart attacks and stroke by at least 20 percent. It can also reduce the risk of high blood pressure, type 2 diabetes, and colon and breast cancer. Exercise can help to keep bones and joints healthy, reduce stress and depression, and lead to more restful sleep.

How do you judge the rate of your physical activity? Moderate activities should allow a person to talk, but they should not be able to sing. Vigorous activities would allow only a few words without stopping to catch a breath.

Couch potatoes take notice, now is the time to begin an exercise regime, it will not get easier if you wait. If walking to the corner is a problem, walk halfway the first few days, and increase the distance as time goes by. Results will be noticeable sooner than you may think, and not only will you feel better, you will look better. With regular activity you may really like the way you look in the mirror a few months from now.