LANDSDOWNE, Pennsylvania -- In the back of her two-story brick colonial, in a small patio-sized add-on, Valarie Arms adjusts a valve on her miniature indoor pool and watches a churning current shoot out like a small stream.
With mounds of snow sitting just outside her windows, she maneuvers into the 91-degree current and starts to backstroke in place, part of a swimming routine that helps her arthritis.
"It has tremendously improved my quality of life," said Arms, an English professor at Drexel University. "Somebody just this week asked me if I've seen my chiropractor, who is kind of a friend because I saw him so much, but I haven't seen him this year."
Swim-in-place pools or swimming treadmills or Endless Pools (a brand name) are gaining popularity among baby boomers whose creaky knees can no longer take a pounding, avid swimmers, people seeking a healthier lifestyle and those who need medical rehabilitation. The $23,900 baseline price is seen as a worthy investment, and that thinking has translated into increased sales.
"It's amazing what it's done for me," said 70-year-old Anne Banse, who suffers from arthritis, has two artificial knees and recently had back surgery. Before the surgery she swam 20 minutes five times a week.
"I get in there, the water is heated to 85, and I just come out ready to start the day," said Banse, who lives near Philadelphia. "It was so tremendously the right thing to do."
The pools average 8 feet by 15 feet and 3 to 5 feet deep. The top models shoot out a wide, deep and steady stream of water that turns the over-sized bathtub into a lap lane that never ends.
Aquatics expert Tom Griffiths, who wrote about swim-in-place pools in his book "The Complete Swimming Pool Reference," said swimming in the "wet treadmills" is great exercise because there's no stress on hips, knees or ankles.
"There's a lot more people swimming for fitness today, and usually to swim for fitness you need a long lap pool, and this puts a lap pool in a very small space," said Griffiths, the director of aquatics at Penn State University.
Boomers lapping up the products
Pool owners rave that they can swim year-round, that the pools require minimal maintenance and that flip turns aren't required every 25 yards. The pools can be put anywhere -- from basements to garages to gorgeous skylight-laden additions.
Endless Pools, headquartered 20 miles outside Philadelphia, in Aston, was started in 1988 by 32-year-old James Murdock, a Princeton University engineering graduate. He calls an Endless Pool "the perfect product for an aging population."
"We have very sedentary lifestyles, and I think this is going at the heart of that," he said.
Endless Pools, the industry leader of the residential swim-in-place pool, has seen sales take off. Revenue grew from $100,000 in 1989 to $22 million in 2003, on sales of 1,100 pools. Murdock said Endless Pools could sell 3,000 a year in five years. He's eyeing Britain -- and its cold, wet climate -- as a burgeoning market.
Murdock said his average customer's household income is $100,000. Most buy a pool for fitness, but many use them for conditions like multiple sclerosis or post-polio.
The pools aren't found only in homes. The polar bears at New York's Central Park Zoo have an Endless Pool in their icy tank, and vacationers swim in place on Princess cruise ships.
On a recent blustery Sunday, Arms and neighbor Joanne Boyle did water aerobics while Arms' grandson and Boyle's son -- two goggled 5-year-olds -- alternately paddled in the current and filled their bathing suits with air from the side whirlpool jets.
Vincent Boyle, playing lifeguard in a nearby chair, said his wife would love a swim-in-place pool of her own.
"We belong to the Healthplex, but she swims here more often," he said. "I guess you can't beat the convenience of it all year-round, right in your own home."