By Leigh Belanger

Every year on January 2, millions of Americans go on diets. Whether it's part of a New Year's resolution or an antidote to six weeks of holiday eating, the January diet is as American as the Christmas binge.

But most people who gain between a half-pound and a pound during the holidays don't successfully lose the weight and keep it off.

It might be because many Americans don't exercise regularly, and the cold, dark winter months can be a tough time to stay motivated on a new fitness plan. But don't let the frosty weather and short days keep you inside.

A winter exercise plan is a great tool for weight and mood management.  

Feeling sad?

Winter depression, also called SAD, or seasonal affective disorder, is a biochemical  imbalance brought on by lack of light and sunshine during winter. Most people affected by SAD experience mild depression often classified as "winter blues."

Exercise can help relieve the winter blues by giving you an activity to focus on, by helping you sleep better, and by giving you a sense of accomplishment. It's thought that exercise lifts levels of endorphins, and relieves physical tension as well.

Feeling cold?

Head indoors: chilly weather challenges our motivation for outdoor exercise, but that's hardly an excuse to stay couch bound. Join a gym - if your budget is tight, community centers and the YMCA often have inexpensive services. It's estimated that 12 percent of a gym's new members join in January, eager to work fitness into the New Year.

A gym membership is a pass to learn all types of new exercise, from aerobics and spinning classes to strength training and the latest trends in yoga, Pilates, and functional fitness.

Take advantage of the classes and trainings your gym offers-keeping your routine varied and exciting goes a long way towards maintaining your motivation. A varied fitness routine also keeps your body challenged and makes it a more efficient calorie burner.

Or bundle up: With the proper attire, exercising outdoors in cold weather doesn't have to be a bone-chilling affair. Whether you're running, skiing or skating, it's important to dress appropriately and keep moving.

Try these suggestions:

•  Dress in layers. Your base layer should be made of a fabric that wicks moisture away from the skin. Cotton absorbs moisture-and a sweaty base layer can chill you. Wear a middle layer for warmth, and an outer layer to protect you from wind, snow, and rain. 

•  Wear a hat. Up to 40 percent of our body heat is lost through the head. Gloves, too -- fingers and toes are susceptible to frostbite.

•  Stay visible. For running outside during the winter months, choose light colors and reflective gear so you'll show up while running on dark evenings.

The great outdoors

Whether you're outdoors or indoors, keep your workouts varied. Recreational winter sports, like ice skating, hockey, and cross-country or downhill skiing, will keep you fit while having fun.

Ice skating can burn up to 600 calories an hour, and gives a low-impact workout that focuses on lower body strength, balance, and cardiovascular fitness.

Cross-country skiing is thought to be one of the best forms of aerobic exercise. It's a total body workout that's low impact and intense at the same time. As your arms work the poles, your legs stride with the skis -- and these long strides work to strengthen and lengthen your muscles.

Hockey and downhill skiing are both more high-impact than cross-country skiing and figure skating, but the overall fitness benefits are the same. If you've been working in the weight room, stretching, and doing regular cardio, your body will be ready to take on some intense outdoor exercise.

Protect yourself

Just be sure you protect yourself from the elements. Our bodies are susceptible to frostbite and hypothermia when exposed to cold temperatures over time.

Frostbite, which targets your nose, ears, cheeks, toes and fingers, occurs when a body part has frozen. It causes loss of color and numbness in the affected area, and can result in amputation if severe.

Hypothermia occurs when your body loses heat faster than it's produced. Prolonged exposure to the cold will cause your body to use up its stored energy. This can lead to a drop in core temperature and hypothermia.

If a person's temperature falls below 95 degrees, it's an emergency and medical attention is needed.

However, both hypothermia and frostbite are preventable conditions. If you're well prepared for cold-weather exercise, you'll be able to avoid the risk and focus on the fun.