The next generation is the anti-gravity treadmill.
You pull up a plastic cover, zip it around you, and use air pressure to literally take some of the weight off.
"It allows you to run or walk anywhere from 20 to 100 percent less of your body weight. So it's very much like being on air," said YMCA executive director Monica Garza.
40 year old Brad Stephenson is a San Antonio attorney who suffers from muscular dystrophy. He's in a wheelchair much of the time, except when he's getting his heart rate up on the anti-gravity treadmill.
Stephenson said, "You're able to un-weight your body so it just feels like a balloon blowing up underneath you. It sort of lifts you up and sort of gives you support."
Allison Espinoza is training for a marathon, but her shin splints have made training painful. With this machine, she can exercise without pain.
Garza said, "It's also very similar to doing a water aerobic workout where you're getting the same type of workout but you're just really not offering that impact to your knees, your ankles, or your hips."
The Alter G is based on NASA technology and some of the folks who use it say it feels like what they imagine walking on the moon must be like.
For brad, it's been an important part of his wellness.
He said, "I depend on it now."
The YMCA at Tripoint on St. Mary's in San Antonio is the only public facility in south Texas with an anti-gravity treadmill. You don't have to be a member to try it out or to use it.