Rx: One hour of weight training 3 days a week if you do your whole body at once (4 days for half an hour if you split it up), plus 45 minutes of cardio 5 days a week (it's more than in the 20s and 30s but with less impact and intensity). Take one day off.
This is the decade of the triple whammy: gravity, hormones, and yet more slowing of metabolism as lean muscle mass continues to decrease and body fat increases. Even women who don't put on a pound may expand, according to Pamela Peeke, MD, author of Body for Life for Women. "After 40 and certainly after 50, virtually all women find that they gain fat more easily in the torso—below the bra, through the triceps area, on the back, and in the belly," she says. "You're not doing anything wrong; your body composition is changing."
Cardio work at least three days a week is still important for keeping weight under control, but resistance training is crucial now. "Women should be doing more weight training—and really going for it," says New York City based celebrity trainer Kacy Duke, who is in her 40s. "You have to find the time to do it consistently and train hard." If you're just starting, says Peeke, "you must learn proper form—take a class, get a trainer, make sure someone is there to correct you so you don't get hurt. And add intensity."
Certain body parts may call out for extra attention. "Pilates can help some with the midsection," says fitness veteran Karen Voight, who teaches and writes a workout column for the Los Angeles Times. To tone the back of the upper arm, she instructs, "get on all fours in a bent-knee push-up position, with fingers facing forward and hands directly under your shoulders. Make sure your elbows point backward when they bend, and lower only halfway, which works the muscle but avoids strain on the joints." Then there's the butt. "For that," says Voight, who is in her 40s, "I'd try squats with weights or stair-climbing."
It's also about enjoyment. "I find exercise that's satisfying on a deeper level," says Donna Richardson Joyner, 43, creator of the video Sweating in the Spirit and a recent appointee to the President's Council on Physical Fitness and Sports. "It's not just about moving my body—it's about strengthening my mind and my spirit."