"Use it or lose it" has become Dean Constantine's mantra.

Over the years, the 79-year-old former dance instructor has suffered back problems, underwent knee and hip replacements and, at one point, found it too hard to walk or drive. But it was doing nothing that really did a number on him.

When Constantine discovered that inactivity was causing his muscles to atrophy, he decided to fight back. Like millions of Americans, Constantine was feeling the effects of sarcopenia, age-related muscle wasting, a condition that's largely preventable.

For more than two decades, doctors have known that adults who don't have a strength-training regimen risked losing 1/2 to 2 percent of muscle mass a year between ages 30 and 80. And, more recently, a study at Harvard University concluded that even the very elderly can improve their muscle mass, strength and gait after just eight weeks of high-intensity strength training (see the study at tinyurl.com/2ar9t9m), proving that you're never too old to benefit from exercise.

But doctors, trainers and researchers say that too many baby boomers are settling into their 60s inactive -- and unaware.

"Sarcopenia is definitely at the forefront of public health concerns for primary-care physicians for individuals over about the age of 60," said Luke Carlson, owner of Discover Strength in Plymouth. "I definitely have some clients [who] heard from their physicians or just noticed themselves that, 'Hey, my muscles are wasting away and I just basically [am] not able to do the things that I used to be able to do.' They come to us saying, "I need to do something about this.'"

Trainer Jody Lessard agrees. She regularly sees evidence of sarcopenia in clients at the YMCA in Shoreview.

"I can pick them out," she said. "You can just see their legs are dragging a little bit and they are very unstable. There is no muscle mass. It looks like [they] just took the cast off after six months. Their legs look totally atrophied."

That's what had happened to Constantine, who was determined "not to get any worse." He started working out with trainer Mike Bialick at the Marsh in Minnetonka."I was just very weak. I asked him to stop the rusting," said Constantine, who taught ballroom dancing for 58 years.

Bialick put Constantine through twice-a-week weight training and, because Constantine had back problems, Bialick also recommended rowing exercises to improve his posture. Bialick also suggested that Constantine exercise daily on his own.

"You have to start strength training and really push the muscles," Bialick said. "It doesn't have to take a huge amount of time. Even if you can devote 20 to 30 minutes three times a week, you can get significant results."

Constantine can feel the difference. "At first I could not even drive my car. Getting in and out was too hard," he said. "Now I can do more. I can go on the treadmill and ride my bike, walk up and down stairs." Of his trainer, he said: "He pushes me pretty well."

That's the point.

Chris Coffey, a physiologist and co-owner of the Institute for Exercise Medicine and Prevention in St. Paul, said that workouts to keep muscle tone "should be vigorous. Just because you are 75 or 80 years old doesn't mean that you can't push your body."

And Coffey knows his message isn't just for 80-year-olds.

At 42, Coffey is noticing age-related changes in his own body. Ten years ago, he regularly leg-pressed 1,000 pounds. Today he's down to 560.

"I can tell my strength is going down, so I have had to come up with a new formula of workouts" that maintain muscle mass and strength, he said. "I refuse to accept that I am going to be a victim. I am going to be driven. I am not going to let sarcopenia kick in."

He gave that same piece of advice to his mother, Pat Coffey, 68, who was so out of shape after foot surgery three years ago that she couldn't get out of a chair without pushing off on something.

"The surgery laid me up for a good six weeks," she said. "And the muscles around my knees and thighs got really weak because I wasn't walking."

Her son gave her a year of fitness training as a Christmas gift. It took six months, but she graduated from getting out of a chair to doing wall squats and push-ups.

Now she has advice for the rest of us: "Get off your butt. That is it, in a nutshell."

Dee DePass • 612-673-7725