The common assertion that adults gain a whopping five pounds or more over the winter holidays is wrong, report researchers from the National Institutes of Health and the Medical University of South Carolina.

But before you down an extra eggnog to celebrate, here's the bad news: "Weight does increase significantly during the holidays," according to their study, published in last month's Obesity Research journal. The average weight gain during the holiday period from mid- or late November to early or mid-January is "only 0.81 pounds," they note.

Holiday pounds aren't inevitable, however. Accumulating 30 minutes of moderate physical activity on most days of the week can help prevent weight gain, this study and others suggest. More extensive exercise may even result in weight loss.

Yet this is small comfort to America's sedentary majority, who cite "lack of time" as the main reason why they don't exercise. If they can't fit in fitness during the rest of the year, how can they find time to exercise during the time-crunched holiday season?

The secret, says fitness expert Peg Jordan, is to "take all the dreaded 'shoulds' out of exercise."

All too often, "people finish a long, hard day at work, then tell themselves they should go to the gym," says Jordan, an Oakland, Calif., registered nurse who is editor of American Fitness magazine.

"If you don't exercise, you not only blame yourself for making the wrong choice, you also reinforce a negative pattern of 'should, but didn't,' and start to label yourself an exercise failure," she writes in her new book, "The Fitness Instinct" (Rodale Press, 1999). "If you do exercise as a 'should,' you end up hating every minute of it."

As an alternative, Jordan suggests "checking in with yourself physically to determine what your body needs at the moment." This is accomplished with a simple technique called a body scan: Close your eyes, take a deep breath, exhale slowly and scan your body from head to toe.

Your scan will probably find you to be in one of four physical states of being--fatigued, tense, languid or dynamic, says Jordan, who has traveled the world studying the movement habits of diverse cultures for a doctoral program in medical anthropology.

When you do an activity you enjoy that is appropriate to your energetic state, she says, it relieves stress. But when you force yourself to do an inappropriate exercise you feel that you "should" do, but dislike, it can add to your stress.

"Movement is good medicine, but only when the choice of movement fits the physiological need," says Jordan, who advises these different activities for each energy state:

* Fatigued. When you're "too tired," replenish your energy with gentle movements that act as turbines to recharge your batteries. Energy generators include swinging a golf club or baseball bat, jumping on a mini-trampoline and practicing tai chi or yoga.

* Tense. If you're "too wired," unwind with de-stressing soothers such as walking meditation, swimming, stretching, aikido or moving to music.

* Languid. When you're "too uninspired," re-energize yourself with creative movement such as dancing (belly, jazz, salsa or swing), gardening or building sand castles.

* Dynamic. If you're "too mired" in a rut, try a movable treat to restore a sense of play and nudge your body into new challenges. These extroverted moves include kickboxing, martial arts, body drumming, kayaking, in-line skating, orienteering and rock climbing.

All these activities share a characteristic that Jordan says is too often missing from "hard body" exercise programs. "They're fun," she notes, adding that this "joyful factor" in movement helps connect mind and body, which boosts the therapeutic effect. This connection is blunted when people 'check out' during exercise--for example, by watching TV while on a treadmill.

"Exercise has become equated with calorie-burning and dry, boring training recommendations," says Jordan, who blames an overly commercial fitness industry for pushing intimidating messages and an "unrealistic pursuit of perfection."

A healthier approach is to "listen to your body's natural instinct for movement," she says, "and replace the drudgery of exercise with a welcome, playful movement experience."

Unfortunately, many people find this extremely difficult because "they live in a disembodied state," says Jordan. In a world where people drive to work, sit at a desk, come home and sit in front of a TV or computer, she says, "we are out of touch with our bodies."

She contends that the natural instinct to move, present in children, is "insidiously squashed" over the years by adult insistence on sitting still, then is further dampened by cultural misconceptions that "fitness is something beyond our reach." Yet fitness has less to do with an "idealized" appearance than with your ability to perform the activities of a typical day.

True fitness isn't achieved by pushing yourself to do tedious routines you hate, she says, but by "regaining the playful sense of joyous movement" and making it part of each day.

One of the best ways to do this--and fit in exercise during the busy holiday season--is to "have a real old-fashioned holiday where you do things the way your grandmother did them."

For example:

* Use muscle, not machines. Turn off the bread machine and mix, knead and pound the dough yourself. Chop wood, bike to the store, rake leaves, climb the stairs, carry your groceries.

* Socialize outdoors by taking walks, building a snowman or going skating, sledding or skiing.

* Play indoor games such as table tennis, bowling, Twister and charades, or turn on the music and dance.

Reinforce these active behaviors with a "post-movement" treat such as a peppermint foot massage or warm bath scented with aromatic oils. "This extends the enjoyment," Jordan says, "and continues the association between movement and pleasure."