It was probably no surprise to the Limas household in Chicago that daughter Arlene grew up to be a fighter.

Being raised in a house with four brothers, she said, was like living in a carnival fun house: You never knew what would spring from around the next corner. The ability to duck or punch or roll was part of the lifestyle.

But holding your own against a gang of siblings is one thing. Winning Olympic gold is another. Limas traveled to Seoul in 1988 and captured the women's welterweight title in the martial art of tae kwon do, South Korea's national sport. She went on to win two world championships in the sport and top honors in the Pan American Games, and she retired undefeated from international competition in the early 1990s.

Today she runs her own dojang, Power Kix, in Stafford, Va., a spacious studio where she both trains young athletes and poses a challenge to some of our notions about middle age and fitness.

If "aging gracefully" is one goal, perhaps Limas can add a dimension: aging with power.

At 42, she remains lightning quick, with a thunderous side kick. When she does a flying kick alongside the high school students and young adults she trains for national competition, she matches them inch for inch off the ground.

Limas now sprinkles softball and flag football into her palette of activity and recognizes that she needs more rest and recovery than she did back in the days of eight-hour training and sparring sessions.

"I want to feel invincible," she said, "but I had to say ... 'It's OK being fit and being in better shape than most 42-year-olds.' "

She does it largely by continuing to practice and share with others a discipline she has been studying in various forms since she was 5. Tae kwon do is known for its powerful arsenal of kicks, and during a recent workout at her gym, Limas discussed how the principles she uses to train black belts can help us all maintain speed, strength and balance as we get older.

For many of us, exercise involves an activity done at a fairly steady speed for a certain amount of time. We run five miles at a 10-minute-per-mile pace; do our half-hour on the elliptical; ride a bike for couple of hours on the weekend.

That's great for the heart and great for SOME of our muscle — the slow-twitch fibers that are wired and built for endurance activities.

But we are born with a different type of muscle as well: the fast-twitch fibers that are activated by a different type of neuron and play a different role in our physiology.

If you think about what most of us do for exercise, those fibers probably don't get enough attention (and may as a result be the likeliest to atrophy as we age).

Jumping, kicking, punching — the sorts of quick, full-range plyometric movements that helped Limas fend off her brothers and her competitors in Seoul — call those fibers into play.

The warm-up for a typical training session at Limas' studio, for example, includes sets of five jumps, knees as high to the chest as possible.

There are bouts of stair running — not interminably long climbs, but quick bursts up only seven or eight steps. Limas' students might go one step at a time at first, then do two or three at a clip to extend the leg as in a kick. They hop up the stairs as well: up two, then down one, in a forward-and-back pattern that requires body control to complement leg strength.

It can be done with intensity, of course, but anybody with a staircase at home can use this piece of "equipment" as they wish by walking a bit faster at first, for example, and trying to gradually increase speed.

And there is kicking (lots of kicking), an activity that seems intuitive to kids but gets forgotten somewhere along the path to civilized adulthood.

To watch Limas' students kick a target is to understand how little kicking has to do with the legs and how much it has to do with balance and coordination in the rest of the body.

To feel them do it (holding a practice pad and bracing for the impact) is to realize just how much power a 120-pound high school girl can generate when she puts her mind and hips into it.

But here's the key: A kick needn't be black-belt quality to help with balance, muscle control and other things we'd like to hold on to as we grow older. You can do a simple two-step exercise lying on your back: "raise" the knee to hip level, then extend the foot. You can progress to doing the same with one hand on a wall or chair for balance, before letting go altogether. Start slowly, but try to make the kick quicker as you get used to the motion.

When you're ready to make contact, have a partner hold a pillow or cushion at hip level, facing the ground. While kicking air is fine, actually hitting something is good for the bones and ligaments and muscles (and maybe the soul as well).

Limas builds those sorts of adaptations into her classes as needed. Roughly a third of her 400 students are adults, many of them beginners who have taken up tae kwon do to support or participate alongside their children.

With the bloody spectacle of extreme fighting now so common on television, the idea of pursuing martial arts for everyday fitness might seem distasteful.

It would be wrong to draw that parallel. Across the spectrum of fighting sports, there is a large number of styles. Each has its own ethic and emphasis — from boxing to the close-contact of Israeli Krav Maga to the spinning and rolling of Japanese aikido.

Even tai chi, practiced most commonly as a slow, meditative set of movements, is at its root a martial art.

Some styles use more kicking, some more punching, some more grappling or other techniques. All share this: They are great exercise, both physical and mental, that call on your body to move in ways and directions that you'll never experience on a piece of cardio equipment. And though they might seem exotic or even dangerous, a good teacher can safely train students of any level.

And, to our point, any age.