Ladies, go take a hike. Or at least a brisk walk.

Seriously. It may lower your risk of stroke and prevent the dreaded middle-age weight gain, new research shows. These findings join a long list of reasons why you should remain physically active.

And almost no one knows those reasons better than Miriam Nelson, 49, director of the John Hancock Research Center on Physical Activity, Nutrition and Obesity Prevention at Tufts University in Boston and co-author of a new book, "The Strong Women's Guide to Total Health," with Jennifer Ackerman.

Nelson is one of the country's leading researchers on exercise for women, and she co-chaired the committee that created the government's 2008 Physical Activity Guidelines for Americans.

Many women complain about gaining weight during and after menopause, but a recent study found that some normal-weight women were able to prevent weight gain by doing an hour a day of moderate-intensity physical activity such as brisk walking.

Say what? An hour a day?

That amount is doable for most women, Nelson says, but it takes effort to do more activity all day long, including while traveling to and from work, socializing and playing with your kids or grandkids.

Almost nothing is easier and cheaper than walking, but that means you need to get the lead out and put some spring into your step. It's not window shopping or taking a stroll in the park. "Brisk means that you get warm while walking and that, while you can carry on a conversation, you can't just gab forever _ you need to speak in shorter sentences," she says.

"You should feel that your heart rate is elevated. But it is not so intense that you are sweating a lot, unless, of course, it is hot outside. And remember that exercise intensity is relative. A brisk walk for one lady may be a stroll for another."

Many women do less exercise as they age when they need to be doing as much or more, Nelson says. "It may be that we are exercising the same number of times a week, but the actual energy used during that time may be less because we aren't working out at the same intensity or speed. Also, we may be doing slightly less activity around the house with chores and gardening."

Plus, many women don't strength-train, which means they are losing muscle mass, says Nelson, who has done numerous studies and books on the benefits. Lean tissue is what is metabolically active, she says. Loss of this tissue contributes to slowing metabolism.

Weight training benefits the body in numerous ways, including improving bone, joint and muscle health; boosting the immune system; reducing depressive symptoms; and improving sleep.

You can do as little as two sessions a week at a local fitness center or lift weights at home, she says, but make sure you're challenging yourself and lifting enough weight. Another great option: sit-ups, lunges, squats, push-ups and pull-ups, she says. You can do them on your living room floor while watching the news or playing with the kids.

And now is certainly not the time to ignore your diet. One of the major keys to avoiding middle-age spread: closely monitoring your caloric intake, Nelson says. By far the biggest culprit of weight gain as people age is eating too much, she says, especially foods high in sugar and added fat.