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.