You're pedaling hard through the Chinese countryside, past red pagodas and pink flowering trees that sway in the breeze. Your heart's pumping, and you can almost feel the calories burning away. But there's trouble ahead. A serpentine green animal slithers into view. It has a large mouth, a long tail—and wings. Fortunately, the S3 is built to handle dragons. You just shoot them down by squeezing the triggers on the handlebars.

Obviously, the supernatural chase is unfolding in a videogame. But what might be surprising is where it's being played.

The S3 was created by Expresso Fitness, a Sunnyvale, California-based startup that's among several pioneering a new kind of exercise experience—some call it "exertainment"—for the videogame generation. The Web-connected recumbent exercise cycle, with a 19-inch L.C.D. screen, hit health clubs across the U.S., from Crunch to Gold's Gym, this fall.

"Games have been around for 25 years," says Expresso C.E.O. Brian Button, "and it's amazing that people haven't used them for more active entertainment before."

Gyms, health facilities, and even schools have been adopting existing videogames for their exercise regimes. The dance-pad videogame Dance Dance Revolution was among the first to get gamers sweating. The EyeToy, the motion-tracking camera for Sony's Playstation 3, has been used for aerobics in games such as EyeToy Kinetic. In May, Nintendo introduced the Wii Fit—a wireless balance board used for yoga and pilates and even snowboarding—to wide acclaim and sales. According to NPD Group, a technology research firm, the Wii Fit sold 1.1 million units in its first two months alone.

"What's so interesting about Wii Fit and other games that encourage people to get moving is that they have grown legs of their own," says Marc Franklin, a spokesperson for Nintendo of America. "We have seen gyms, schools, hospitals, physical rehabilitation centers, and other facilities incorporate these games into their programs without any encouragement from us."

Keith Worts, chief operating officer of Crunch, which has 30 gyms nationwide, has introduced the Expresso bikes at some of his facilities and is now looking at bringing Wii Fit titles into the gyms too. The hope is to draw new members who don't ordinarily like to exercise. "These new technologies and initiatives are innovative and can help take your mind off the fact that you're exercising, which can be a painful thing."