“Shape-shifting” is something most women know about all too well. As the years pile on, so do unwanted pounds that-even among those who remain relatively slim-can literally change the body’s contours.

“One may go from an hourglass to more of a shot glass,” says Dr. Pamela Peeke, a clinical assistant professor of medicine at the University of Maryland School of Medicine, best-selling author and creator of the “Body For Life For Women Workout” DVD (rodale store.com). “Aging gracefully is all a matter of girth control.”

Not to mention understanding women’s hormones.

It’s Peeke’s assertion that recognizing what she calls “women’s unique hormonal hard-wiring” is key to achieving and maintaining a peak body for life. There are four hormonal milestones involved:

• Teens and Twenties. This is when estrogen production rises. Women who were skinny teens may suddenly find weight going to their breasts, hips and thighs. This is the time to build a strong fitness foundation that can last the rest of your life. It’s also a good time to build muscle tone and minimize body fat changes.

• The Reproductive Years. Science shows that if you enter pregnancy healthy and fit, you’ll have a healthier nine months and a healthier baby. Whether you have children or not, this is the time when your metabolism begins to slow down. During this period, you should add resistance training-weights-to keep your metabolism as hot as you can.

• The Forties. This is a time of shape-shifting. Fluctuating estrogen and progesterone levels lead to a three- to five-pound potbelly, or menopot, for many women-on top of which toxic stress levels boost your food cravings. You need to regroup, ramp up your physical activity, examine your lifestyle and put things into balance.

• Menopause. Once you’ve reached this milestone, it’s important to exercise the mind and body so that you stay sharp and keep fit. Keep learning. Make the effort to add resistance training and cardio-revving walks every day. Your goal is to live a long and indepen-dent life by taking good care of yourself.

Whether you’re 20 or 50, Dr. Peeke’s new DVD, “Body For Life For Women Workout,” can help you.