In as little as a month your family can make a dramatic change from sluggish to rugged. Multiple studies show that it takes just 30 days to make exercise a habit. If you're a family of four, assign each person a week in the next month to be the family's fitness coach. The coach selects a week's worth of activities (start with three). Some suggestions to get you started:

* TWIST AND SHOUT. Play five or six straight games of Twister to give everyone a good stretch and sweat, says Jessica Walker, an exercise physiologist and registered dietitian at Caritas Medical Center in Louisville, Kentucky. Sneak your spouse a few kisses as you pass him in the tangled mass.

* HIT THE MALL. If the outdoor temperature is too cold, head to the mall. Spend the first half hour walking laps, then reward your kids by letting them browse in their favorite stores. If the mall's not for you, briskly walk a museum. Take breaks at interesting exhibits. Many schools open their gyms to the public in the winter as well. Call and ask if yours does.

* HIT THE CIRCUIT. Create an at-home training circuit with four different exercise stations, such as running the stairs, jumping rope in the rec room, doing sit-ups in the living room, and stationary biking in the basement. Do each activity for a minute or so and keep rotating for half an hour, says Sharon B. Spalding, professor of physical education at Mary Baldwin College in Staunton, Virginia. The rapid rotation keeps things from getting dull.

* COUNT STEPS. Get everyone a $5 pedometer from your local department store and make it a contest to see who takes the most steps that day, says Walker. The winner gets to pick out a rental movie or other fun prize.

* DANCE UP A STORM. Put on your dancing shoes and blare your music of choice, whether it's the Beatles or the Wiggles. Dancing can burn 75 or more calories every 15 minutes. "Kids always get a kick out of watching their parents dance," says Dr. Vera Frumin, chair of pediatrics at Holy Redeemer Hospital in Philadelphia.

* HIT THE POOL. Community rec centers and local schools often have open pool nights during the winter. "Nothing beats the winter blahs like jumping in a pool," says Walker.