Whether it's because of the restraints of ever-shrinking back yards or the ease of maintenance, swim spas are adding a new look to outdoor recreation.

Swim spas, designed for exercise and therapy, were in abundance at the International Pool and Spa Expo in Las Vegas last December.

And not to be outdone, one company offers an option to build a conventional swimming pool with a water treadmill. Similar equipment can be used to retrofit a swimming pool into an exercise machine.

Here's what several companies displayed:

Rio Plastics. Swim spas come in a variety of sizes and shapes, from a 19-by-71/2-foot pool that is 5 feet deep and has a separate spa to a 141/2-by-71/2-foot pool with a pool and spa depth of 33/4 feet.

With the push of a button, powerful swim jets convert the swim spa pools into a workout area for swimming, aquajogging and exercising. The attached spa with separate temperature controls on the 19-foot model adds hot water for a relaxing experience after the workout.

Rio Plastics, a Brownsville, Texas, producer of Aqua Swim 'N' Spa, touts its fiberglass swim spas for stress relief, general pain relief, health, fitness and entertainment.

Details: www.rioswimspas.com.

Ferno Performance Pools. This company in Wilmington, Ohio, offers fiberglass swimming pools ranging up to 40 feet long and outfitted with variable-speed swim systems. The Ferno pool products mostly are intended for commercial uses, but they can be placed in home back yards.

The Triathlon Swim Spa is tailor-made for long-distance training and has jets that provide resistance for swimming. Adding a new dimension to the workout is the Triathlon Treadmill and Swim Spa, which has a treadmill built into the pool's floor.

Ferno also offers the Aquagaiter, an underwater treadmill that makes it possible to convert conventional swimming pools into aquatic exercise and therapy pools. The removable treadmill offers a rigorous cardiovascular workout with reduced impact on joints.

The Ferno Water Bike uses the natural buoyancy of the water to help the user reduce the impact on joints while maintaining or regaining muscle strength, flexibility and range of motion.

Details: 1-888-206-7802; Ferno PerformancePools.com.

Speck Pumps. This Jacksonville company makes a number of pool products including swim-jet systems that can turn a pool into a lap pool or a water treadmill.

The company's Badujet and Badustream jet systems provide resistance for a walk, jog or vigorous swim. The adjustable systems can create a current in excess of 5,000 gallons per minute. There also is a massage hose than can be attached to a jet nozzle to provide a pulsating massage.

Both systems perform the same functions, but the Badustream has more convenience features. They can be built into any type of pool, new or existing. The systems are available through pool professionals.

Prices listed on the Web site are for various packages, depending on how you plan to use the jets. A single jet, for example, would be for someone who might want to do water aerobics while a three-nozzle system would be for the competitive swimmer. You can expect to pay around $4,000 for the Badujet and from about $2,000 to $6,000 for the Badustream. Installation costs are additional.

For more information, visit usa.speck-pumps.com or obtain a free video by calling 1-800-223-8538.