ATLANTA, Georgia (CNN) -- An hour on horseback once a week is more than just fun for Will Hillis. It's therapeutic.
Will Hillis, 8, takes part in hippotherapy. The horseback therapy helps him gain physical and emotional strength.
The 8-year-old from Dunwoody, Georgia, has cerebral palsy. He can't walk, and he has difficulty sitting up, but while riding on the back of a horse he gains physical and emotional strength and confidence.
"When he's up on the horse, he loves it," said his mother, Kay Hillis. "He never wants to leave."
Will is among a growing number of children and adults in the United States who take part in physical, occupational and speech language therapy on horseback.
The treatment is called hippotherapy. Hippos is the Greek word for horse. While the American Hippotherapy Association doesn't keep track of the number of participants, it counts among its members more than 650 physical therapists.
"For hippotherapy, you're actually using the horse as a treatment tool," said Brent Applegate, Will's physical therapist who is based at the Chastain Horse Park in Atlanta. "You're using the movement of the horse in your session to achieve the goals you want to achieve."
A horse provides a base of support during a therapy session. To stay on the animal, the patient needs to use his or her stomach and lower body muscles. Health Minute: More on horses and physical therapy »
Bonnie Cunningham, executive director of the hippotherapy association, said hippotherapy was once regarded as an alternative therapy because it is recreational. As the concept catches on around the country, it is entering the mainstream, Cunningham said.
Applegate describes hippotherapy as a combination of balance and coordination techniques that prepare some patients for eventually sitting upright or walking.
Hippotherapy also can be used to help improve sensory and visual problems. It is recommended for people with autism, developmental delays, learning disabilities and recovery from stroke and traumatic brain injury.
Horses are specially selected depending on their demeanor, mannerisms and movements. "Some horses have more movement; some horses have less movement," Applegate said. "Some give a lot of lateral movement. Some give a lot of rotation."
Safety is a primary concern, according to Applegate. "You want a good horse that's not going to spook -- that's going to be what we call bombproof."
Will begins many of his hippotherapy sessions on an artificial horse called an equicizer. Applegate climbed on the apparatus with him and spent 15 minutes helping stretch the muscles in his legs, arms and hands.
Then, it's time to mount a real animal. Applegate lifted Will onto a horse named Pooh Bear.
After donning a helmet and getting strapped in to the stirrups, Will gave the horse a one-word command: Walk. Along with Applegate, two assistants helped control the horse and held Will steady. The group took it slowly, up and down hills before entering the corral.
"Will's biggest issue is trying to sit up on his own," Applegate said. "Will has to fight to keep his balance."
Applegate said Will has made steady progress in the six months he's been riding. Will also attends traditional physical, occupational and speech therapy every week.
Kay Hillis said hippotherapy is making a big difference for her son. "Every little bit of progress is wonderful for me as a parent. I've seen his upper body strengthen, and he's sitting up better," she said.
The sessions aren't cheap. Hillis said her insurance company covered the first 20 visits, but now she pays out of pocket. Applegate estimated some therapists charge up to $200 for a one-hour session.
Parents such as Hillis note that the therapy is worth every penny. "He loves it here," she said of her son. "Horse therapy has been very good for him."
Applegate agreed that Will and other patients benefit emotionally. "The one thing I don't have to worry about out here is motivation. I mean these kids are out here riding on a horse. How cool is that?"
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