From a NY Times article, 5/13/08 by Gina Kolata (Summary: Healthy muscles are those that have been worked, stressed and pushed to their limit so that they have enough power and strength to get you through life, especially as you grow older…Older people often fall because they are too weak to brace themselves)

DR. PAUL D. THOMPSON, a 60-year-old marathon runner and chief of cardiology at Hartford Hospital, stood in front of a medical audience recently and began his talk with a story about himself.

“I’ve been lifting weights since I was 12 years old and look at me,” he said. Dr. Thompson is small and wiry with not a bulging muscle on him. He speculated that he must have a genetic inability to build muscles, no matter how hard he works at it.
But are his muscles healthy?

It is not the kind of question most people ask themselves. But muscle researchers say it is important because muscle health is emerging as an important part of overall health. And, they say, when it comes to muscles, bulk does not matter. How big they can become depends on your sex as well as genetics. What matters for health is whether, like Dr. Thompson, you use them.

Healthy muscles, researchers say, are those that have been worked, stressed and pushed to their limit so that they have enough power and strength to get you through life, especially as you grow older. And keeping muscles fit takes effort, which means regular training with weight lifting and cardiovascular exercise even if the results are not a sculptured look, these experts add.

If you don’t work your muscles, they will atrophy, especially as you grow older. Older people often fall because they are too weak to brace themselves, and they have trouble with steps and opening jars because their muscles have lost so much strength. Much of that loss can be avoided, muscle researchers say. Even elderly people can gain muscle strength if they work at it, studies have shown.

There are two aspects to healthy muscles: endurance and strength, said Robert H. Fitts, an exercise physiologist at Marquette University and chairman of the biology department there. To maintain endurance, you should engage in activities that pump blood to the muscles, like walking. For strength, you need to lift weights, concentrating on what Professor Fitts calls the antigravity muscles, those of the back and legs. And, he adds, you should also maintain arm strength.

But while many people walk, fewer lift weights, and those who do often use incorrect techniques, said William J. Kraemer, a professor of kinesiology at the University of Connecticut.

Some try to do it on their own but tend to buy weights that are too light and may not know the well-researched methods that get results.

Others go to gyms, where they may be intimidated when they venture into weight rooms filled with people grunting and straining and machines that can seem daunting. Those who do try to lift at the gym can end up using weights that are not heavy enough to fully stimulate their muscles.

That is especially true of women, Dr. Kraemer said, even those who work with personal trainers. While women often say they are afraid they will bulk up, this fear is unfounded, Dr. Kraemer and others say. Acquiring muscle mass requires testosterone levels that women don’t have. Instead, the toning that many women say they want comes from lifting heavy weights.

The most effective way to stimulate muscles is with a system known as progressive resistance. This approach can take about three hours a week and includes days, once a week or so, when you lift weights so heavy that you can do only three to five repetitions before your muscles are too tired to lift again.

Other days are devoted to moderate resistance, with weights you can lift 8 to 10 times. And then you should have some light days, with weights you can lift 12 to 15 times before your muscles tire.

It may sound like a lot of effort, but even people like Dr. Thompson, who does not acquire bulk, benefit.

“I still lift,” he said, “because it makes doing other stuff — yardwork, carrying groceries, carrying grandkids — easier. “I think some folks outlive their muscles, meaning that they are fine mentally and cardiacwise but have so little muscle strength that they can’t catch themselves with their other leg when they start to fall,” Dr. Thompson added. “And if they fall they cannot get up.”

He does not want to be one of those people.