If there’s a magic pill for staying youthful, it may be one that’s hard to swallow: exercise. Daily doses have been proven to thwart a number of aging factors — stress, obesity, heart disease, diabetes — and the longer you’re physically active, the less you’ll notice getting older.

Weight training is good at any age.

The catch is that a 50-year-old’s body is not the same as a 20-year-old’s; you can’t push it the same way you once did, nor should you if you want to keep it in working-out order.

So listen to these coaches — they’re talking not just professionally but also firsthand — on how to remain fit, and proud of it, through the decades.

Find the perfect fit for any age!

There’s a big difference between how we should work out in our 20s and how we should work out when … we’re no longer 20. Find your perfect fit.

The 20s

Rx: 30 minutes of weight training followed by 30 minutes of cardio 3x a week, plus 45 to 60 minutes of straight cardio 3x a week. One day of rest.

The great thing about being in your 20s is that your body is so strong, you can get away with abusing it. The bad thing is that you often do, punishing it with late nights and bad eating habits. And you routinely fail to appreciate what you’ve got.

This is the decade of anxiety — frantic exercise, fad diets, the mad pursuit of pinup perfection and self-hatred when you fail to meet it. The fitness challenge of these years: Get over it.

“I tell my young clients, ‘Forget looking like Jessica Simpson or Halle Berry, and forget weight; think health,’” says Jeanette Jenkins, 32, a Los Angeles based private trainer who has worked with rapper Queen Latifah and actress Taryn Manning.

The mistake many 20-somethings make is simply opting for “endless cardio and crunches,” adds Vanessa Carver, 25, a personal trainer at Fitness Quest 10 in San Diego, whose clients include professional ice skaters and dancers.

Lots of cardio is great, she says, especially if you mix it up so you’re really pushing the body. But it’s weight training that builds muscle definition, not to mention bone density, which will be crucial for staying active later on and preventing osteoporosis.

“You’ve got to lift more than just three or five pounds,” she says. “If you can do 10 to 15 repetitions of a weight with no real effort, it’s too light. The last four or five reps should be challenging enough that you feel your muscles getting fatigued.” And put your mind into it, she says. “Lifting weights while chatting on the cell phone is a joke.”

The 30s

Rx: One hour of circuit training (cardio and resistance) 4x a week, plus at least one day of cardio for 45 to 60 minutes at a high intensity. Take one day off.

With the 30s, you start noticing that weight doesn’t come off quite as easily as it used to. This is because after age 20, your basal metabolism drops by 1 to 2 percent every decade, and as lean muscle decreases and body fat increases, you don’t need as many calories to sustain yourself.

“Exercise is the number one form of preventive medicine,” says Jillian Michaels, 32, who was a trainer on the first three seasons of NBC’s “The Biggest Loser” and is the author of “Winning by Losing: Drop the Weight, Change Your Life.”

“You won’t see that big a difference between 31 and 39 if you’ve been living a healthy lifestyle, but if not, you’ll see a huge difference in muscle tone, weight, and shape.”

In this decade, experts agree, keeping fit means working harder. Jenkins favors circuit training — a series of resistance and cardio exercises done swiftly and back-to-back. But however you do it, Michaels advises strength training each muscle group twice a week with two days of rest between sessions. Don’t stick with heavy weights/low reps or low weight/many reps, she says; switch it around to keep your body from getting used to the routine. One day of rest a week is crucial.

After pregnancy a program like Pilates can be invaluable in “pulling everything back in and up,” says Brooke Siler, 38, whose re:AB studio in New York City has attracted famous figures like Amber Valletta, Madonna, and Liv Tyler. “I especially like exercises that involve standing, because they teach you to fight what nature wants you to do, which is slump,” says Siler, the author of “The Pilates Body.”

Now is the time to make good fitness habits a part of everyday life. “You always want to be standing instead of sitting, taking stairs instead of elevators,” says Siler. “I’m constantly aware of how I sit and stand and walk down the street. I’m forever pulling in and up. These invisible workouts are really important for a woman in her 30s. It’s how you start preparing your body for what’s to come.”

The 40s

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, M.D., 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.”

The 50s

Rx: 4 to 6 cardio sessions a week, 20 to 40 minutes each, with an intensity that lets you answer a simple question but not chat, plus half an hour of weight training twice a week, 8 to 12 repetitions of each exercise, or 15 to 20 using lighter weights. Always stretch afterward.

If your metabolism feels like it’s slowing to a crawl, it’s not in your mind. Researchers at the University of Pittsburgh studying 541 midlife women found an average gain of 12 pounds eight years after menopause. We also tend to gain a little potbelly, what Peeke calls the menopot. And other places begin to droop noticeably. “At this point, loss of muscle mass and tone really shows,” says longtime fitness expert Kathy Smith, 54. “It can actually start to change your posture.”

The classic shoulder slump from years of hunching over a desk or computer “will really age you,” says Smith, who suggests this stretch: Clasp your hands behind your back at the level of your butt and squeeze your shoulder blades together, pinching your spine. Try, with straight arms, to stretch your fingertips toward the floor until you notice a tug between your ears and shoulders, then lift your hands as high as you can, feeling the stretch in your chest.

“If you haven’t started weight training, you must,” says Smith, “although if you’re a beginner, I really recommend guidance. Women in their 70s have doubled their strength in nine weeks. If you feel intimidated going to a gym, you can rent videos to do at home. You want to hit all the major muscle groups, and you can do the whole cycle in 15 minutes if you keep some dumbbells around.”

Yoga — along with tai chi, dance, and the Bosu ball (a soft half-dome used for standing and sitting exercises) — is great for balance, which will become an increasingly important issue. While the physical changes this decade brings may be hard to take at first, ultimately, says Smith, “you shift into an acceptance mode. You change what you can, and live with what you can’t. It’s a gentler way.”

The 60s

Rx: 3 days a week of challenging but not exhausting cardio, such as a slow jog, plus 3 days of weight training, using lighter weights and slower, more controlled movements combined with slow, sustained stretching. Walk whenever possible, and do daily balance exercises.

In the 60s, problems like arthritis, bad knees, and spinal stenosis (a narrowing of the spaces between bones that can put painful pressure on the spinal cord) become common.

“But aches and pains shouldn’t be an excuse for giving up on exercise,” says Marilyn Moffat, Ph.D., a professor of physical therapy at New York University and co-author of “Age-Defying Fitness.” “We now know that a decline in strength and fitness isn’t entirely a natural consequence of the aging process but is also due to lack of use. We need to push ourselves physically no matter how old we are — we just may need to alter the activity.”

Adapting a workout routine for the 60s sometimes means giving up aerobic exercise that jars and stresses the joints — for example, replacing long runs with jogging one or two miles, jogging in a pool, swimming, or riding a stationary bicycle. (Women with bad backs may need to use a recumbent bicycle.) Moffat, who is 65, says that, on average, she walks three to five miles a day because it offers both cardio and bone-strengthening benefits.

Resistance training is still important, “but I would not advise anyone to lift heavy weights if it aggravates your joints,” Moffat says. And stretching and balance are absolute musts. If you don’t stretch now, “by the time you’re in your 80s, your joints will have lost their flexibility.”

One of Moffat’s favorite stretches is holding the head tilted earlobe to shoulder for 60 seconds; another (if you don’t have osteoporosis) is sitting on the floor with legs straight out in front of you, feet flexed, and lowering your head toward your knees. For balance, she suggests “rising up on the toes of one foot and trying to hold the position for a minute. You can do this while brushing your teeth.”

In fact, that’s a good image for any age — the sooner exercise becomes like brushing your teeth, the longer you’ll feel younger than your years.

Teen Girls Report Barriers To Physical Activity

05 Apr 2006

Teenage girls perceive lack of time as the number one barrier to physical activity, according to a new study published in the March issue of Medicine & Science in Sports & Exercise�, the official journal of the American College of Sports Medicine (ACSM). The three-year survey assessing black and white adolescent girls reveals sedentary habits are mostly linked to internal barriers (interest, motivation), which were unrelated to external factors (jobs, recreation).

More than half of approximately 2,000 girls surveyed from ages 16 or 17 to 18 or 19 were identified as being sedentary. Of those classified as sedentary (about 1,000 girls), the majority (65 percent for black girls and 80 percent for white girls) claimed lack of time was their primary barrier to activity. They also frequently said they were too tired or uninterested in participating in physical activities. Other commonly reported barriers, such as safety and body image concerns, came from the 10-item questionnaire developed to assess the girls’ perceptions of barriers to activity participation.

With the identification of these barriers, researchers corroborated with other information about the girls to understand whether barriers were simply perceived or were related to external circumstances. For instance, while the majority of girls felt lack of time prevented their pursuit of activity, researchers found no difference in hours at work or in household chores when compared to girls who did not report time as a barrier. Further, girls who said they were too tired had about the same amount of sleep per night as those who did not report fatigue.

“Overall activity levels have declined by 83 percent in these age groups,” said Sue Y.S. Kimm, M.D., M.P.H., lead author of the study. “These girls are definitely at risk for becoming overweight or obese, if they are not already, because of this steep decline. Recognizing what these girls perceive as barriers to their health and wellness can help us motivate them to find balance in their life that includes an increase in energy expenditure.”

Other findings from the study showed habitual physical activity was significantly lower among black girls; these girls spent twice as much time watching television or videos and were significantly heavier than white girls. More white girls reported lack of time, and also were significantly more likely to indicate fatigue and self-consciousness as a barrier to exercise. Black girls were more than twice as likely to cite safety as a concern, although this was not one of the leading barriers to activity participation. Researchers were interested to find that black girls cited fewer barriers overall, and suggested the greater decline in activity participation may reflect cultural differences and attitudes about exercise.

“We don’t know as much as we’d like about why girls become particularly inactive during adolescence,” said Kimm. “Our evidence suggests the two most commonly cited reasons – lack of time and fatigue – are probably not actual barriers because these girls did not work more hours after school or have less sleep than others. However, it’s the perception of a barrier we must overcome in order to help these girls find the time and energy it takes to get moving.”

ACSM and the U.S. Centers for Disease Control and Prevention recommend 30 minutes of physical activity on most, if not all, days of the week. For those who perceive lack of time as a major barrier, health and fitness experts agree physical activity can be accumulated during the day in shorter periods of activity, such as 10- or 15-minute bouts.

The American College of Sports Medicine is the largest sports medicine and exercise science organization in the world. More than 20,000 international, national, and regional members are dedicated to advancing and integrating scientific research to provide educational and practical applications of exercise science and sports medicine.

Medicine & Science in Sports & Exercise� is the official journal of the American College of Sports Medicine , and is available from Lippincott Williams & Wilkins at 1-800-638-6423. For a complete copy of the research paper (Vol. 38, No. 3, pages 536-542) or to speak with a leading sports medicine expert on the topic, contact the Department of Communications and Public Information at 317-637-9200 ext. 127 or 117. Visit ACSM online at http://www.acsm.org. The conclusions outlined in this news release are those of the researchers only, and should not be construed as an official statement of the American College of Sports Medicine.