(CNN) Belle Swersey knows firsthand how therapeutic horseback riding can be. The 7-year-old girl, who is in remission from a rare type of muscle cancer called rhabdomyosarcoma, has been using equine therapy to help ease her pain for the past 2½ years.
"Horseback riding helps me forget about my cancer. It's fun," said Belle, of Newton, Massachusetts.
Belle's dad, Jonathan Swersey, was skeptical of the practice at first. But he soon realized that it was transforming his daughter's ability to cope with the side effects of chemotherapy and radiation.
"It's helped her a lot with pain management. When Belle started, she was taking oxycodone, and the oxycodone was really ineffective for her pain. It was really incredible to watch her riding a horse for the first time. She had no sense of pain whatsoever," Swersey said.
Belle significantly reduced her reliance on oxycodone after starting the therapeutic riding program, he said. The equine therapy was more effective at treating her pain than medication.
She takes therapeutic riding lessons at Friends For Tomorrow, an organization in Lincoln, Massachusetts, that helps more than 60 people every year, according to its website.
"I also feel very strongly that it gives her a sense of control over things in her life when she hasn't always had a lot of choices about things," Belle's father added. "And the fact that the horses are such big animals, I think, also makes her feel stronger."
The therapeutic benefits of horseback riding have been referenced since antiquity. In the fifth century BC, the Greek physician Hippocrates -- namesake of the Hippocratic oath -- wrote a thesis called "Natural Exercise" that references the therapeutic value of horseback riding, according to the American Hippotherapy Association.
A number of services that involve horses are available for individuals with special needs; they include adaptive (or therapeutic) horseback riding lessons, equine-assisted learning and mental health services. In addition, occupational therapy, physical therapy and speech therapy services can include equines, equine movement and the equine environment in treatment. When this is done, it is referred to as "hippotherapy," according to Tina Rocco, president of the American Hippotherapy Association.
"The benefits of incorporating the horse in treatment by licensed occupational therapy, physical therapy and speech language pathology professionals are well supported in existing research. Such research is emerging in mental health. Research regarding the benefits of recreational activities involving equines such as therapeutic/adaptive riding and horsemanship lessons is limited," Rocco said in a statement.
But more recently, the benefits of equine therapy have been subject to debate. Despite extensive anecdotal evidence supporting the use of horses in the treatment of a variety of conditions such as autism and cerebral palsy, the field lacks a canon of high-quality research, according to Michael Anestis, associate professor of psychology at the University of Southern Mississippi.
"There's not evidence that equine-assisted therapy is dangerous or doesn't work; there just isn't evidence that it does," said Anestis, who authored a 2014 study on the topic.
"If somebody goes through equine-assisted psychotherapy and they get better, awesome. I'm happy for them. My career does not hinge upon this working or not working. I just want people to get better," he added.
The lack of evidence may stem, in part, from a lack of common terminology. A number of practices are often referred to as "equine therapy," including therapeutic horseback riding, equine-assisted psychotherapy and equine-assisted activities such as horse grooming and stable management.
"Part of the problem is that they're so diverse, and some trials cite things that aren't actually the same thing as what they're doing. What even is this treatment?" Anestis said.
The American Hippotherapy Association provides continuing education to licensed occupational therapy, physical therapy and speech-language pathology professionals and maintains best practice statements for licensed therapists who incorporate horses into treatment. Certification in hippotherapy as a clinical specialty is available through the American Hippotherapy Certification Board, according to Rocco.
The Professional Association of Therapeutic Horsemanship International, or PATH, is one of two major organizations in the United States that certifies centers in equine-assisted activities and therapies; the other is the Equine Assisted Growth and Learning Association.
Since its founding in 1969, PATH International has certified about 880 member centers around the world in various types of equine-assisted activities, according to Kaye Marks, director of marketing and communication for PATH International.
" 'Equine-assisted activities and therapies' is an umbrella term, and all of the different types [of activities] fall underneath our umbrella," Marks said.
In 2016, PATH-certified centers served over 66,000 individuals around the world, including over 6,000 US veterans, according to the organization's 2016 fact sheet.
"PATH International is known for our standards for certification and accreditation. They cover everything from best practices in safety to business practices in management to humane treatment of animals," Marks said.
The price of equine-assisted activities and therapies varies based on the location and type of service. At Friends For Tomorrow, a PATH-certified center, each hourlong therapeutic riding lesson costs approximately $80, according to head riding instructor Lucy Cornish.
Insurance does not normally cover these services. TRICARE -- which provides health benefits to members of the military, veterans and their families -- has covered hippotherapy in some cases, according to Marks. But upcoming research could convince other insurers to cover it, too.
"The new research is going to change everything for us. Once that starts happening and we get more medical providers that are on board and they talk to insurance companies, I think something might really happen," she said.
One important distinction in the field of equine-assisted activities and therapies is the difference between therapeutic horseback riding and hippotherapy.
Therapeutic horseback riding refers to a recreational activity in which a non-therapist riding instructor teaches an individual how to actively control a horse while riding. It has been promoted as having substantial health benefits for such individuals as kids with autism or veterans with post-traumatic stress disorder, according to Carolyn Garver, director of the Dallas Autism Treatment Center and leading author of a 2011 study on the topic.
"Veterans do really well with equine-assisted activities. Same with at-risk youth. It gives them a lot of self-confidence. It gives autistic children a lot of self-confidence, too," Garver said.
"It's also good for people that have motor disorders: cerebral palsy, tic disorders. I think it has a lot of ramifications for many different disabilities," she added.
Garver's study followed 20 children with autism over six months of equine-assisted activities such as horseback riding. The children's average score on the Childhood Autism Rating Scale dropped from 37 at the beginning of the study to 34 at the end.
The Childhood Autism Rating Scale is a 15-item scale used to evaluate symptoms such as poor verbal communication skills and flattened emotional response. A score of 30 or more is often used to diagnose autism in children, and a score of 37 and higher indicates severe autism, according to the study.
"Autism consists of social/communication disorders and behavioral/sensory disorders," Garver said. "They can also have restricted or repetitive interests. And a horse can feed into that because they're very repetitive and always have the same gait.
"I have a number of kids that ride, and it just seems to really relax them," she added.
But despite these promising results, the study suffered from a number of limitations -- particularly, the lack of a randomized control group.
"There have been a lot of obstacles that have prevented great research from happening," Marks said. "But I bet that in another five years, we're going to be able to point people in the direction of some really great research."
By comparison, hippotherapy is a specific type of intervention in which physical therapists, recreational therapists, occupational therapists or speech and language pathologists use the movement of the horse to improve the rider's posture, balance, coordination, strength and sensorimotor systems.
Treatment incorporating hippotherapy is not recreational in nature, according to Rocco. It falls under a medical model and has been recognized for decades as a treatment tool that be can be used within a therapist's scope of practice, she said.
Hippotherapy is thought to improve symptoms of cerebral palsy -- such as poor coordination, stiff muscles and muscle weakness -- by stimulating many of the muscles used in coordinated movements. The gait of the horse is also thought to mimic the rhythm of a human walking, according to Marks.
"When they've measured the gait of the horse, it's so consistent with walking," she said. "Once a person is mounted on a horse, the muscles that they're using to stay balanced on the horse and to keep good posture on the horse are consistent with the muscles that they would be using if they were moving on their own."
A 2003 study provided some evidence for the use of hippotherapy in treating cerebral palsy. Fifteen children with cerebral palsy were randomly assigned to either eight minutes of hippotherapy or eight minutes of stationary activity. Those who received hippotherapy showed significant improvements in coordinated muscle activity immediately after the treatment.
However, the study was limited by its small size and inability to show long-term improvements in muscle coordination, according to Anestis.
There are nearly 100 peer-reviewed journal publications and eight systematic reviews showing support for the use of hippotherapy by occupational therapists, physical therapists and speech language pathologists, according to Rocco.
But continuous research and large, randomized control studies evaluating the effectiveness of various types of equine-related activities, as well as therapy services incorporating equines, are still needed, she said.
Some organizations have even begun funding research of their own.
In 2017, the Horses and Humans Research Foundation raised nearly $200,000 to fund research advancing knowledge of horses and their potential to affect health and well-being, according to the foundation's website.
Some studies have shown significant improvements in scientific rigor. A 2015 randomized control trial involving 116 autistic children ages 6 to 16 showed that a 10-week regiment of therapeutic horseback riding significantly improved symptoms of autism such as irritability, hyperactivity, social cognition and social communication, compared with a control group.
Those children who engaged in therapeutic horseback riding also showed significant increases in verbal communication skills, including the number and types of words used.
"This is by far the most well-designed clinical trial of equine-assisted psychotherapy I've seen," Anestis said of the study.
Still, he has concerns about how the research is being presented to consumers.
"I'm concerned about what percentage of practitioners of equine-assisted therapy are fully informing their patients about what the evidence base actually is for equine-assisted therapy," he said. "And without that, clients cannot make informed choices about their health care."
But according to Garver, that should not prevent people who are interested in equine therapy from giving it a shot.
"Try it," she said. "You need to find a reputable program that has experience with people with disabilities, which I'm sure most of them do. But there's a lot of them popping up."
Because for some, such as Belle Swersey, the physical and emotional benefits of equine-assisted therapies have been life-changing.
"In our situation, we were willing to try anything that might help," Belle's father said. "And I think it's been shocking and so wonderful to see how effective it's been.
"I just can't even begin to tell you how thankful we are to be able to have this."