Mary Ann Wilson could well be the perfect Spokane celebrity.

She’s quiet, unassuming, down-to-earth — just like the city itself.

If you saw her in the supermarket, which you just might have, you likely wouldn’t know she’s the star of a TV show airing on 116 stations in some 63 million households around the country.

“I’m like the most shy person in the whole world,” Wilson says. “None of this is natural for me.”

The nature of her show, “Sit and Be Fit,” is just as humble as she is: On each episode, Wilson sits in a chair and leads an exercise routine. Sometimes she’ll spice things up with a towel for resistence, or maybe an exercise ball, or a bag of lentils to add weight. But “Sit and Be Fit” pretty well sums it up.

Her low-tech show even caught the attention of late-night talk show host Jimmy Kimmel, who recently made hay of Wilson’s modest persona. (“He can be a little on the naughty side,” says Wilson, who adds that she did invite Kimmel to appear on her show, but he never responded.

Despite, or, more likely, because of the program’s simplicity, Wilson has won legions of fans, largely of the “Greatest Generation” set. Her followers have arthritis and Parkinson’s and weakness caused by strokes. But woe to the PBS station that threatens to take “Sit and Be Fit” off the air — Wilson has several inch-thick binders crammed with fan mail and testimonials, some of the 125 letters she gets each week.

“If it weren’t for you, I would not be walking,” wrote one. “You are the Mother Theresa of us arthritics,” wrote another.

The show, which is produced and taped at the KSPS-TV studios on the South Hill, has been on the air for the past 18 years. Wilson and her crew just wrapped up 20 new episodes and plans are in the works for another batch this summer.

So, how did this registered nurse, mom of four and grandmother to 12 become the most unlikely of TV stars?

Wilson’s life changed one day in 1970. Her husband was playing handball and dropped dead on the court of a heart attack. She was left a young widow, with kids who were just 2, 5, 7 and 9.

As much for a mental break as a physical one, Wilson started taking an hour-long exercise class five days a week.

High-impact aerobics were all the rage then, but instructors knew they were missing an audience of potential exercisers who were not up for such intense workouts.

So, course programmers from Spokane Community College asked Wilson to develop a stretching and toning class for seniors in 1985.

“With each class, the age range kept going up,” she says.

She wanted participants to develop better posture, to retain their independence. She focused on breathing and limited repetitions.

“I wanted them to leave with energy,” she says.

They left with more than just energy. Class members started telling Wilson their fingers were now limber enough to hold a pen for the first time in years. They had the flexibility to turn their heads again. They were less afraid of falling.

“They were like miracles in class,” she says. But, even with all of those successes, Wilson felt discouraged.

“I thought, ‘I’m touching so few lives here,’ ” she recalls.

She knew she needed a wider audience.

So, she started making a pitch for a TV show to all of the local stations. She pursued KSPS for nine months and was about to give up when she finally got the go-ahead, with one caveat:

Wilson, who had never been on TV in her life, would have to tape 30 shows in two weeks.

“I got two hours’ sleep a night,” she says.

But, still, Wilson wanted her message of fitness for all to reach more people.

“I said, ‘I don’t want this to be just a local program,’ ” she says. ” ‘I want this nationwide.’ “

That first year, about three dozen stations signed up to air the free program.

“It just kind of grew from there,” she says.

Bob Lawrence, a producer and director at KSPS, has worked with Wilson ever since the show began.

“I thought it was great; it was a niche that really wasn’t being filled,” Lawrence says. “It’s very thorough and very researched.”

Just a couple of years after starting the program, though, Wilson fell ill.

“I thought I was dying,” she says.

Doctors diagnosed her with chronic fatigue syndrome, a disease marked by crippling exhaustion, aches and pains, vertigo and other symptoms. It knocked her out of commission for three years. She was barely able to move, let alone tape new shows. But the re-runs kept airing.

One day, while lying on the couch, she started watching her own exercise program.

In a surreal moment, the Mary Ann Wilson on the screen told the woman on the couch, “If you can roll a shoulder, you can do something in this program.”

Wilson was able to do just two minutes of the routine that day. But, with the help of continued exercise, dietary changes and acupuncture, she got well again.

And in the years since, “Sit and Be Fit” has taken over Wilson’s life. Apart from her bedroom and kitchen, Wilson’s entire South Hill home has been swallowed up by the business. Offices are set up in each bedroom, where employees take phone calls, work on newsletters and coordinate with TV stations. Shelves and shelves of videotaped programs take up much of the basement.

In 2000, “Sit and Be Fit” became a non-profit organization, to better find funding sources for the show.

Several times a week, Wilson teaches exercise classes at area retirement centers. She calls them her “laboratory,” where she gets new ideas for the TV program. (Even after all of these years, she says she still hasn’t run out of exercises that can be done while sitting in a chair.)

On a recent day at the Waterford on South Hill, nearly 20 residents gathered in floral upholstered armchairs for Wilson’s class. Some arrived with walkers. At least one was on oxygen.

But all of them clutched their exercise balls and followed along with Wilson’s gentle movements.

“Are you all feeling OK?” she asked the class. “You’re not breathless?”

Waterford resident Rose Hopkins, 88, has been attending Wilson’s class for three months, after suffering a stroke about a year ago.

The regular routine has helped her recover, Hopkins says.

“I’m exercising, which I hadn’t been doing,” she says. “I feel better. She’s wonderful. It gets us out here, that’s for sure.”