A resistance pool at the St. Joseph Institute, a wellness spa in central Pennsylvania.

ST. JOSEPH INSTITUTE

Your body has its own hydraulic system, Jenny Sheetz tells me. The massage therapist and co-owner of Pennsylvania’s St. Joseph Institute spa says she can feel the fluids moving as she holds my ankles while I lie fully clothed on a massage table. Fill. Pause, two, three. Release.

Sheetz says she can feel my cerebrospinal fluids circulating through my body, just as you can feel the heart pump when taking a pulse. My fluids, she tells me, are moving like water through a partially clogged kitchen pipe. The amplitude is weak, the rhythm restricted, with no symmetry in the various touch points. She says she can fix that.

Time for some craniosacral therapy and somato-emotional release.

Those are two of a variety of therapeutic treatments available at St. Joseph’s, a “wellness spa” in central Pennsylvania that is part of one of the biggest new trends in travel. It’s also part of what is by far the largest new trend in the spa industry.

A wellness spa typically offers all the massages and facials and wraps you’d expect at any day or destination spa, but with an additional array of health services — sometimes mainstream, sometimes alternative and sometimes a bit of both. Although no one has yet definitively described what makes a wellness spa, it’s a little like pornography: You know it when you see it.

Using that loose definition, the International Spa Association identified 310 wellness spas in the United States in 2004; last year, the trade group counted 915. Wellness spas produced $469 million in revenue in 2006 — a leap of more than 340 percent in two years.

And at $155 a night for two on weeknights, including dinner, St. Joseph’s is among the least expensive.

I don’t have the medical expertise to judge whether the treatments accomplished what they’re supposed to, but they sure felt good to body and soul. And if you consider peace and quiet an important component of wellness, I can tell you that spas don’t get a lot more rural than this one.

We turn off a two-lane road to an empty stretch that is about a lane and a half, both sides lined with forest. I get increasingly excited about spending a night at a rural retreat with spa. My mother, in the passenger seat, is not impressed.

Speaking like a true country girl who couldn’t wait to move into town, she complains, “Who’d want to come way back here in the boondocks?”

Me, a transplanted city girl, for one.

We drive through the open iron gates and park in front of a stone and wood building nestled in the woods. The air smells of pine and fireplaces. Inside the spa, sun streams through oversize windows and the smells of jasmine, rosemary and the oils of exotic flowers fill the air.

OPENED ABOUT a year and a half ago, St. Joseph’s is in the pretty much nowhere town of Port Matilda, about a half-hour drive from Pennsylvania State University’s main campus in State College. Many guests come simply for pampering with regular spa treatments, others in search of life transformations.

Treatments include acupressure and other “healing massages,” exercise and diet programs, and laser treatment to increase range of motion and provide pain relief for ailments such as carpal tunnel syndrome and sports injuries. You can just get a facial, or get treatments said to be good for autism or arthritis.

Set the controls to high on the resistance pool, where you swim in place as the current passes you by, and you can get a 6-mph swim — an Olympic-training-level cardiovascular workout. But if you’re recovering from an injury, the staff will oversee a gentle, rehabilitative workout.

Take a sauna in steam infused with essential oils just because it feels good, or ease your aching back with a readjustment by the on-call chiropractor. If your issues are emotional or spiritual, they have programs for that, too.

I FOUND St. Joseph’s at SpaFinders.com, in the “medical/wellness” listings. This category includes spas whose medical services may be limited to a couple of alternative therapies with an Eastern or New Age bent — for instance, maybe nutritional advice and some relaxation techniques such as yoga. At the other end of the spectrum, your wellness spa vacation could include a huge range of mainstream medical treatments delivered by board-certified doctors, sports therapists and nutritionists, complemented by naturopathic experts trained in Chinese medicine, massage therapists who can both pamper and treat your ailments, and maybe a mental health expert.

Take, for example, Canyon Ranch, which operates resorts in Tucson, Ariz., and Lenox, Mass. Each facility employs seven board-certified physicians, and the company has hired Richard Carmona, who until recently was U.S. surgeon general, as chief executive officer of medical services. Canyon Ranch has state-of-the-art medical equipment, in addition to treatment facilities manned by Chinese herbalists, acupuncturists and other specialists in alternative and preventive care.

A full medical exam can include a bone density scan, a Pap test and a full body scan for measuring lean body mass.

Some procedures, particularly those that are mainstream, such as a Pap test, may be covered by health insurance, but it’s up to you to pay, then fill out the insurance paperwork that might bring some reimbursement.

You can find the extreme end of thoroughness in the medical spa field at the Medical Spa at Nova, in Ashburn, Va., about a 10-minute drive from Dulles International Airport. The spa, with massage therapists and health and fitness experts, is connected to medical offices housing physicians with numerous specialties and a naturopathic practitioner trained in Chinese medicine. Those offices are in turn connected to an urgent care center.

St. Joseph Institute falls somewhere in the middle of the continuum. Sheetz and her husband, Michael Campbell, are searching for a medical director. Under the supervision of a doctor, their alternative therapies will become “integrative” — a combination of both mainstream and alternative. That will allow them, Campbell says, to take on a wider variety of complicated medical issues.

Meanwhile, they can simply pamper you in a serene setting or provide alternative treatments that alone might help what ails you.

WHEN I ARRIVE at St. Joseph’s, the receptionist suggests I might want to use the “dry hydrotherapy” machine. I climb aboard the bed-like apparatus, which moves heated water under pressure up and down the surface of the bed.

I lie down and soon feel some of the stress of driving three hours ooze from my body. This could change my life; I must have one of these. Campbell tells me they cost $21,000. Oh. Never mind.

I decide to take a walk on paths that meander through the wooded, 65-acre property, and soon encounter a wooden chapel with a simple but elegant design that reminds me of something by Frank Lloyd Wright. The entire front is windows overlooking the woods.

Besides the name of the property and the statue of St. Joseph just inside the spa doors, the chapel is another glaring clue that the owners of St. Joseph’s are Christian. But even the chapel is intended to be nondenominational, Sheetz says. It celebrates spirituality, and the oneness of all faiths, she says. Some guests might go inside to pray, others to meditate. Still others, like me, might find deer grazing outside the windows and find that peaceful and somehow restorative.

I’ve booked time in one of the spa’s nine treatment rooms, but haven’t chosen a therapy. Sheetz suggests craniosacral evaluation and somato-emotional release. Okay.

After evaluating the fluid flow in my body and the six pulse points typically measured by Chinese doctors, Sheetz begins touching my back, chest, stomach. But I hardly notice what she’s doing because I’ve begun to tell her about my life, every major heartache and trauma since childhood. I have a sudden realization and blurt out: “We’re in a counseling session.”

Turns out that in addition to being licensed to do a variety of massage therapies, and in addition to being a nutritionist, Sheetz has a master’s degree in counseling. Various parts of the body, she says, hold certain emotions. She says she can feel the tension easing as I talk and she touches.

Entire books have been written on craniosacral therapy and somato-emotional release, and my paraphrasing of her off-the-cuff explanations is rough at best. All I can say is that when she is done, I feel as if I’ve had a terrific massage, even though I haven’t had a massage at all.

DINNER IS SERVED in the main lodge, which has a main hall with a two-story ceiling and giant windows that frame a big stone fireplace. I sit to watch the fire and chat with a couple who have come overnight just to get away from the kids for a while.

The dining room is just down the hall, a plainer room than the main hall. Guests share a series of wooden tables. The food is simple but delicious. Everything, including bread, soup and salad dressing, is homemade and gluten-free. The next morning after breakfast, I head to the spa with notions of hitting the dry aqua bed again, but buyer beware: The spa is closed on Sundays.

As we drive away down the lonely stretch of country road, I do get some unexpected gratification.

My mother, apparently no longer disturbed by being in the boondocks, mentions how much she liked her lymph massage, said to be good for detoxifying the body and assisting lymph flow. She starts dropping hints about returning.