BACK, hips, knees, balance, cardio - all can be problems for seniors who want to keep fit. But they are no reasons not to exercise, just to work out safety and smart. Leanne Italie visits the gym.

At 45, DeEtte Sauer was a dead woman walking. She was morbidly obese, her heart disease so serious a doctor warned her to expect "an event at any time." Eaten up by her marketing career, struggling to raise three kids, she smoked, drank and never, ever exercised.

Sauer remembers a vacation when - at 5-foot-5 (1.52-meter) and 230 pounds (104.33 kilograms) - she couldn't make it onto a small boat for a day out with her family. "That's when it hit me. I was an elected cripple. I had done it to myself."

She got busy, slowly shedding the weight through sensible eating and exercise. She began to walk around her Houston neighborhood in the United States, then she discovered the pool. Now 69, the woman who once had a supermom complex is a competitive, medal-winning senior swimmer.

"It literally saved my life," Sauer said, adding that her best event is the butterfly - a stroke she learned at age 62.

To trainers with lots of clients well beyond 50, Sauer is the holy grail, somebody who works hard and efficiently, taking care to avoid injury while maintaining motivation, strength and endurance through careful workouts. Getting fit later in life is one thing, they said, but staying that way at 60, 70 and 80 is another.

"Going from running to walking, going from the treadmill to the elliptical as we age. It can be really frustrating, mentally debilitating," says Chris Freytag, a yoga and Pilates instructor and contributing fitness editor for Prevention magazine.

"Even for me. I'm 45 and say, oh God, I can just see it coming. There's going to be some wear and tear. That doesn't mean I have to give up, but I have to make some changes."

Back, hips, knees, balance, cardio - all can be trouble spots and big blows to a positive attitude for seniors, says Freytag and fitness expert Denise Austin, who was Jack LaLanne's sidekick on television and went on to her own workout shows, DVDs and books. At 53, she has a new book out in January, "Get Energy!"

Flexibility

Pilates and yoga are great ways to stay strong and flexible beyond 50 because both can be easily modified, the experts says.

"Your spine is your lifeline," Austin says. "Keep it healthy, keep it strong. As we age we lose flexibility and it's really important to our tendons and ligaments to stay pliable and keep all the fluids in our joints going."

She suggests increasing floor work to take pressure off the knees. Can't touch your toes anymore? Use an elastic band for the same stretch, or to replace weight training that might grow dangerous.

Taking the time to stretch, to reopen joints and muscles after a workout, is increasingly important as we age - particularly crucial at 60, 70 or older, Freytag says. "The lower back and hip flexors get really tight. The two are correlated. What I tell people is you are no longer able to skip stretching after a workout."

Freytag recommends at least five to 10 minutes of stretching after a workout, when the muscles are warm.

Warming up BEFORE a workout is key to balance. For running seniors, Austin suggests five minutes of walking before getting into a gradual run, or intervals of walking and running.

"It's very important as you age to change it up more, to surprise your muscles and work them differently," she says.

Runners may need to balance workouts with more strength training and stretching to avoid hip and knee problems, adding muscle work for the abs is important for balance and flexibility. Add five minutes of strength training and five minutes of stretching, Austin suggests.

"Really concentrate on the center of your body. Your core. It is truly the powerhouse of your body. It affects how you walk, your flexors, it protects your back. That's why Pilates is great."

Balance issues don't have to put an end to staying fit. Work out in a chair or use one to lean on if you're feeling unsteady. "There's a ton you can do in a chair," Freytag says.

Freytag calls balance a "use it or lose it" proposition. "There are so many classes at gyms for folks over 60," she says. "The biggest thing for people who are athletes already is to keep positive and just think about the fact that you're going to train smarter. You're not going to stop. It's just that you have to change."

Cardio work

With heart disease stalking both men and women, aging doesn't have to mean the end to a decent cardio workout.

Riding a bicycle is easier on the hips than running, for instance. Trim back on running to a couple of days a week and supplement on the bike. "You can get on a bike and spin like heck," Freytag says.

For runners who can't bring themselves to give it up, run slower, walk and run, or cross-train. She suggests cardio work four days a week but only at high energy twice in that period.

Dancing is also a good way to get the heart rate up, Austin says. "It changes movements and it changes your muscle twitchings."

At 93, Esther Robinson wouldn't give up her life of fitness for anything. Active all her life, she still hits her local gym ("I like to bench press"), but dancing is something she can enjoy with others.

"When I was 60 or something, I got into square dancing," the great-grandmother says. "I like the music and the movement of it."

Take a page from Sauer's story and hit the pool. "Swimming is easy on the joints. You'll keep your love of sports." Robinson also loves to swim.

Sauer didn't start training hard until 11 years ago. She knew how to splash around, keep from drowning, but "I never had a swim lesson in my life, nothing."

She showed up for her first session at a health club with a 23-year-old instructor "and I couldn't make it across the pool. I wanted to quit. I felt stupid," but he wouldn't let her give up.

"I'm stronger than I ever was at 45. I'm faster," says Sauer, who competes in the National Senior Games and US Masters Swimming events.