DENVER -- Biofeedback, once considered on the fringe of the healthcare profession, is now being used to treat everything from migraines to asthma to incontinence.

It's been around for decades, but now reputable groups such as the Mayo Clinic recommend it and some insurance companies even pay for it.

Still, there could be cause for concern, according to critics.

The idea behind biofeedback is tapping into the power of the mind to control the body.

It may sound metaphysical, but Centennial business owner Jean Hendry is a biofeedback believer.

She has been using it for two years.

"I don't have the stress I had. I don't have the headaches that I had," said Hendry, who was skeptical at first. "But once I felt the results, I was sold."

She's not alone. The alternative medicine technique is now being used to treat a variety of medical conditions.

"Any time there is stress in the body, there's a physical response to it," said Kellie Smith, a Centennial-based biofeedback specialist.

She said the biofeedback machines simply measure the body's response through brain waves, muscle tension, sweat and heart rate.

The information fed back on the computer screen helps people learn to control bodily functions, such as heart rate, using relaxation techniques.

"To me, it feels more like chiropractic was where it was unknown for a long time, and now it's more mainstream. And I think that's what's happening in the biofeedback industry," said Smith.

In fact, at University of Colorado Hospital's Integrative Medicine Center, biofeedback is used right alongside acupuncture and massage as a way to reduce stress.

Denise McGuire, a clinical psychologist with the University of Colorado Hospital, uses biofeedback in her practice.

"It seems to be kind of the best kept secret within the medical profession," said McGuire. "There are no known risks. Basically, it's teaching people how to relax and be able to see on the screen that something is actually shifting in their body."

When the measurements come in, she teaches patients a relaxation technique, such as visualization, guided imagery or deep breathing.

Biofeedback has been used of late to help Olympic athletes better control their bodies with their minds.

"It's been used in a wide variety of ways and even though it sounds New Age-y, it's very, very grounded in science in the medical setting," said McGuire.

In some other setting, though, beware.

Not all products marketed as biofeedback devices are and not all biofeedback practitioners are reputable.

The Mayo Clinic's website warns, "If they claim that it can assess your organs for disease, find impurities in your blood or send signals into your body, it may not be legitimate."

7NEWS found several sites dedicated to exposing biofeedback scams, as well as articles describing the seriously ill not getting traditional medical treatment until it was too late.

For Hendry, biofeedback is a supplement to traditional medical care.

"I would say don't judge it until you've tried it," Hendry said.

However, an hour-long session runs up to $150, which insurance sometimes doesn't cover.

McGuire said patients usually need 10 sessions.

Some critics have claimed biofeedback is much more expensive and no more effective than yoga.