Your friends think you look just fine. You know better.

You know your once incredibly supple and energetic body is now incredibly flabby, fatigued and riddled throughout by carbohydrates. You've been meaning to do something about it.

Some among you can do it alone. Bang. Getting up early morning for pushups, situps, knee bends. Jogging a mile before breakfast. Forsaking Reese's for raisins. Yoga, Hiking, Happy body, happy mind, happy ending.

Some of us, however, need a little help.

A health club, perhaps. There's something about belonging to a health spa that makes exercise a more probable occurrence, and it is money - in particular, money spent. In Washington, one-year memberships at health clubs will cost you anywhere from about $200 to about $500.

There are more than three dozen health clubs in and around Washington Four chains (Holiday Spas, European Health Spas, Barbara Ellen Figure Salons and Fun & Fitness Centers) run 23 of those centers. All but the Barbara Ellens and a few independent woman-only spes are co-ed or open to men and women on alternate days. Most have some kind of exercising equipment and pool, sauna and steam facilities. The membership terms of a few clubs. - Holiday Spas and European Health Spas among them - are somewhat confusing, and sometimes explained a little too quickly. - Most require some kind of physical exam or stress test.

There are things you should know before you walk into the nearest spa, plunk your savings down and sign away rights to your flab. Most places ask you to sign a contract - not a promise to exercise regularly but to pay regularly. Others ask for a lump sum. Some, such as the Holiday Spas chain, will discount the membership price if you join on your first visit. (If you're shopping around, in other words, you should not visit Holiday first).

You should know how long the club has been in operation; if you have doubts about paying for a year's membership at a place that you suspect may close down in two weeks, seek your salvation elsewhere.

Tour the facilities. Ask about hours (and how often they change). Most places offer memberships of varying length and price. Do you really need the Gold Star Lifetime Membership with unlimited use of every facility at every outlet in the continental United States at any hour of the night or day, or is the Bargain Economy Six-Month Special (three nights a week only, good only at your neighborhood club and bring your own soap) a more practical choice?