WHEN MY husband and I invite friends over to "hang out," we're not kidding.We've hung dozens of people --including my 56-year-old mother and a 225-pound medical student -- upside down in the hallway of our Foggy Bottom condominium. The apparatus we use for this bat-like activity is called "gravity inversion" equipment, which consists of a pair of metal and foam boots and a sturdy metal bar.

You snap on the boots, hold onto the bar, swing your legs up, hook the boots to the bar, drop your head down and hang. It's a great way to meditate, exercise or stretch out after a long day's work.

The "gravity inversion" equipment is a major part of what might loosely be termed our "home fitness center." The other apparatus consists of a "rebounder" -- which looks like a small, round trampoline -- and assorted weights for lifting while upside down or right-side up.

For a total cost of about $300 we have all the basic equipment necessary for total fitness -- building strength, flexibility and aerobic conditioning. We can work out regardless of the weather, at any time of the day or night (hanging upside down is a great relaxer if you can't sleep).

But in a two-bedroom apartment, we don't have enough space to centralize all the-equipment. So we rebound in the bedroom and hang in the hall . . .

We bought the gravity inversion boots last spring, after I did a story on the equipment for the Style Plus page. I had first seen them used by actor Richard Gere in the movie "American Gigolo," and got a "hanging lesson" in April from Alexandria distributor John Rush.

Invented by California osteopath Robert Martin to help cure back problems, the equipment is designed to counter the ill effects of gravity's constant pull on the body. Hanging felt great -- particularly on my neck, where I tend to isolate bodily tension -- and the price was right, total cost $110.

Since we bought the boots and bar, we've found hanging beneficial for stretching out first thing in the morning, at the end of the day or before and after exercise. My husband hangs before a handball game; I hang before dance class.

When one person is upside down, the other can grab that person's wrists and pull him or her out. (It may sound like torture, but believe me it's heaven.) And with weights you can pull yourself out. We bought a pair of 3-kilo dumbbells from W. Bell for $11.75, and a pair of 10-pound dumbbells from American Physical Fitness Center for about $20.

The gravity boots spice up any party -- as long as we demonstrate before food is served. People seem to either love or hate being upside down. Most of the people we show it to want to try it. Some have enjoyed it so much they've bought their own gravity inversion equipment.

We keep the boots in a closet, and the bar by itself is fairly unobtrusive. Our cleaning woman uses it to hang up clothes that have just been washed. We haven't quite figured out the best place to keep the weights. Right now they're on a bookshelf. But they do make great doorstops.

We bought the other major piece of equipment, the rebounder, in May. Since I was nursing a knee injury, I had given up racketball and running and wanted equipment that would give an aerobic workout, without putting excess stress on my joints.

At the time, Irving's sports store had them on sale for $119 -- I think they're now down to $99. I got more than a few stares as I carried it down M Street.

The rebounder stays in the bedroom for easy access to the stereo and television -- which keeps a 20- to 30-minute jumping-session from becoming boring. I like rebounding to music -- Stevie Wonder in particular. My husband prefers rebounding to TV -- football games and "M*A*S*H" re-runs are his favorites.

We have yet to find an alternative use for the rebounder -- although people have suggested it looks like a coffee table or a doggie bed. But until we think of something better, for now, when it's not in use we just stand it in a corner on its side.