ALBANY, N.Y. (AP) _ Treadmills still run the show at health clubs and stationary bikes, out of vogue in the 1990s, are making a comeback.
But another piece of workout equipment is making the fastest gains in popularity: the elliptical trainer.
Their use has spiked 158 percent over the past five years, according to the International Health, Racquet and Sportsclub Association, a Boston-based trade association. When the group first began tracking elliptical machine use in 1997, only 1.1 million people used them; that figure is now estimated at 6.7 million.
Interest in elliptical machines and stationary bikes might be explained by the rising number of older Americans in gyms, said Brooke MacInnis Correia, a spokeswoman for the group.
The low-impact workout they provide is appealing to people over 55, comprising nearly a quarter of gym users, Correia said. It also attracts younger athletes and joggers worried about injuries.
``It's not as hard on my knees,'' Albany resident Kris Ditzel said, explaining why he made the switch about a year ago. A runner in his 20s, Ditzel abandoned the treadmill after a leg injury.
Elliptical machines simulate walking, stepping, cycling and skiing; users place their feet on pedals that move in an egg-shaped arc. The user can pick his own resistance or, in some models program a harder workout.
They still lag behind treadmills, with an estimated 10.9 million Americans using them.
``Anybody who knows how to walk knows how to use them,'' said Richard Cotton, spokesman for the American Council on Exercise, in explaining their enduring popularity.
Stationary bicycles, which fell out of vogue in the 1990s, are staging a comeback with up to 7.7 million users in 2004, a 7 percent jump from five years before. At the same time, stairclimbers saw a 26 percent tumble in usage, according to the IHRSA.
Over the past five years, elliptical machines have edged out both Stairmasters and stationary bikes at Bally's Total Fitness, said Matt Messinger, spokesman for the national chain.
While machines may fall in and out of fashion, they all pretty much achieve the same goal, experts say.
``Manufacturers are always trying to show their machines burn the most calories. The bottom line is that if you push yourself to a moderate level, you're going to burn about the same amount of calories,'' Cotton said.
Carl Foster, president of the American College of Sports Medicine and a professor at the University of Wisconsin's Department of Exercise & Sport Science, agreed the differences in the machines' effectiveness are negligible.
``Ambulating _ walking or running _ are probably slightly superior to everything else, but the differences are vanishingly small,'' he said.
The most important consideration, he said, is to pick a machine you like, meaning you'll use it more often.
Each machine does provide specific benefits, however.
Low-impact activities like walking on a treadmill help build bone density and calcium. Meanwhile, elliptical machines _ which often have moveable handlebars that provide resistance _ work out the upper body without beating up joints, said Cotton.
They're also easy to operate.
Walking into a gym and seeing all the machinery can sometimes be intimidating, said Matteo Baker, regional manager for Gold's Gyms in Southern California.
``You get on (the elliptical machine) and there's not a lot to figure out,'' he said.
And then there are people like Michelle Favaloro of Albany who uses different machines to change up her workout. The treadmill is good for getting her legs and heart pumping, and the elliptical gives her an overall body workout, she said.