Maria Birdseye’s right hand trembled as she placed it on her dance partner’s arm.

Her legs were slightly unsteady.

Neither seemed to matter, though, once the music started and Birdseye began to slowly move to the rhythm.

“It’s tiring,” Birdseye, 71, said after an hour-and-a-half lesson that includes a 20-to-25-minute warm-up of stretches, punching and circular hand movements. “But the benefit is that you feel invigorated the next day to do more. I walk farther — I might do 2 miles instead of 1 — and I garden more.”

Birdseye is among nearly two dozen seniors who have signed up for a free adapted tango class at Clairmont Place retirement community. They gather twice a week in a sunlit community room turned ballroom on the first floor to dance the tango.

The class has been offered at other sites. This class runs through Oct. 2.

“Listen to the music, its message,” coos Madeleine E. Hackney, who created the program to help seniors with Parkinson’s disease increase their mobility and cognitive skills. It’s an approach supported by research. “Its message is to move. Relax and shake it out.”

She tells them to close their eyes and feel the music. "One, two, one, two," she says gently. "Then sway, sway."

“No,” one woman chides her peeping partner. “You’re supposed to close your eyes.”

More than a million people in the United States have Parkinson’s, a progressive neurological disease that is characterized by mobility problems including slowness, rigidity, balance and tremors. Some people may also have trouble writing, experience a decrease in facial expressions, fatigue, depression and have trouble sleeping, although symptoms vary by person.

The tango class was designed for vets and/or people with Parkinson’s and their families, friends and community volunteers.

Classical Argentine tango movements have been tweaked for people who may have trouble with their balance, movements or remembering the steps.

“Tango is a very flexible dance,” said Hackney, a former dancer and now a research health scientist at the Atlanta VA Medical Center and an assistant professor of medicine at Emory University. “It’s improvisational, it has a number of steps that challenges balance and it’s aesthetically a very pretty dance.”

Beyond that, the social nature of the partner dance can improve a person’s quality of life and mood.

In adapted tango, steps are modified. For instance, extra steps might be added before a pivot. It uses easier positions for someone whose balance might be off.

Those who need help and a steadier partner are paired with younger staffers or volunteers.

Birdseye, a retired teacher who lives in Decatur, was diagnosed with Parkinson’s disease three years ago. She enjoys the social aspects as well as the exercise.

When she was diagnosed, she admits it was scary.

“I didn’t know whether or not I would end up in a wheelchair,” she said, much less dance.

It’s unknown what causes the disease that usually occurs when a person is in their 50s or 60s, although it has been known to strike people much younger. At least 60,000 are newly diagnosed each year. More awareness has been raised about the disease after celebrities such as Michael J. Fox, Muhammad Ali and Linda Ronstadt revealed they suffer from Parkinson’s.

Research has shown that dance — particularly tango — can be therapeutic for Parkinson’s patients, according to Terry Ellis, a physical therapist and faculty member at Boston University and director of the National Rehab Resource Center of the American Parkinson Disease Association.

“We know exercise is beneficial, and more studies show it should be among the standards of care,” she said. “We don’t really know what is it about tango, per se, that is so special. People with Parkinson’s have difficulty with automatic movement. They can’t turn on that movement. But there’s something about the music in general that makes moving easier.”

Just watch Birdseye.

She’s fine if her dance moves don’t land her a spot on “Dancing With the Stars.”

She’s meeting new friends, even some who are dealing with the same health issues.

“There are people here who are in the same boat,” she said, “and we’re fighting it.”