As the days get shorter and the weather gets colder, one of the challenges facing Lean Plate Club members is how to stay the course with daily physical activity -- an important part of achieving and maintaining a healthy body weight.

"We all have 24 hours a day, but that seems to change at this time of year when it's darker and colder," says Bess H. Marcus, director of the Physical Activity Research Center at Brown University in Providence, R.I. "It makes it seem like we only have 18 hours."

Lack of time -- whether real or perceived -- is one of the major obstacles cited by those who don't regularly get enough physical activity. That can make fall and winter risky seasons for major slippage in the exercise department.

The good news is that if you can keep exercising outdoors as the weather turns colder, you stand to reap a little something extra.

"Estimates are that you burn between 20 and 33 percent more calories" exercising outdoors in cold weather, says Doug McKeag , director of the Indiana University Center for Sports Medicine in Indianapolis. That's because the body has to work not only to keep moving, but also to keep warm.

For many, however, the notion of burning a few extra calories while walking or jogging in cold, nasty weather just isn't enough to justify the effort. "Backsliding is natural during this time of year," notes Glenn Gaesser, professor of exercise physiology at the University of Virginia School of Medicine, who says he skipped two of his daily runs this week when the weather turned cold in Charlottesville. But he countered that with an extra long run later in the week.

It's that kind of adjustment that can make the difference between maintaining your healthy habits during the fall and winter or slipping back into a sedentary lifestyle. And don't forget, besides many health benefits, exercise is a better way to tame an appetite than mindless snacking.

Here's what some experts recommend for cold weather workouts:

CUT YOURSELF SOME SLACK Missing a day or two of exercise isn't the end of the world. Studies show that if you're already exercising regularly, missing a few days won't set you back to your beginning fitness level. "So if you run into bad weather, get sick with a cold or flu and lose even a week or two, it won't take you another three months to get back to where you were," says Gaesser. When it comes to fitness levels, he says, "you can recover what you lost a lot faster than you got it in the first place."

MAINTAIN INTENSITY If the shortened days have eaten into your exercise time, maintain the intensity of your workout. While you won't improve your current fitness level, you can help sustain it. In a study conducted in the 1980s, Gaesser says, researchers trained participants to work out for 40 minutes a day, six days a week. Over four months they then gradually cut the exercise back, first to four days a week and then to just two days. "Their fitness levels didn't drop," because the length of the workout and the intensity stayed the same, Gaesser says. Even when researchers cut the workouts to as little as 13 minutes, fitness levels were maintained -- provided the intensity of the exercise remained high. The take-home message, Gaesser says, is that "if you keep up intensity, you can shave some days and some time."

SET SMALLER GOALS Yes, the latest exercise recommendations from the National Academy of Sciences are to aim for 60 minutes a day of activity to maintain a healthy weight. But 30 minutes on most days is still the recommendation of the U.S. Dietary Guidelines. Studies show that regular exercise helps control blood pressure, reduces the risk of cardiovascular disease and helps to keep insulin levels within a normal range. And studies show that you can do that activity in small increments -- as little as 10 minutes as a time -- and still reap rewards.

MOVE INDOORS No, you don't have to shell out big bucks to join a gym -- although some gyms do offer seasonal memberships. Think shopping malls, community centers, churches and synagogues, which often offer low-cost -- or even free -- exercise options. Another possibility: Set up a circuit in your home; this can be especially good for those days when you can't stray far from kids. Brown University's Marcus, author of "Motivating People To Be Physically Active" (Human Kinetics; 2002), suggests doing 10 push-ups or 10 abdominal crunches. Follow that with climbing the stairs. Then walk a circuit out the front door and round to the back. Repeat multiple times.

BE CREATIVE AND FLEXIBLE Put on music at home and dance. Buy a jump-rope. Pack walking shoes in the car for taking a quick constitutional instead of waiting behind in the carpool line. Rent an exercise video or check one out at the library. Find an exercise buddy. Walk at airports between flights. Sign up for a low-cost weekly exercise class. "The time you put into physical activity more than comes back to you during the day with alertness and energy," says Marcus, who often jumps on a treadmill for a few minutes in between seeing her two children off to school. "Even 10-minute bouts of exercise can help."

-- Sally Squires

How do you plan to stay active as the weather gets colder? Share your tips when Sally Squires hosts the Lean Plate Club, our online chat about healthy eating and exercise. You can join the discussion from 1 p.m. to 2 p.m. today or leave questions ahead of time at www.washingtonpost.com/leanplateclub. To subscribe to the Lean Plate Club electronic newsletter, see www.washingtonpost.com/wp-srv/email/front.htm