ATHENS, Ohio -- When the weather cools, and the leaves begin to turn, outdoor workouts become even more enticing-a long hike on a nature trail, a leisurely run or biking excursion through apple country.

Winter exercise is another matter. Whether you exercise in the morning or late afternoon, you find yourself battling the dark as well as the unfriendly elements. And on those dark winter days when the wind is howling and snow is falling, only the hardy are eager to venture out.

David Eland, DO, associate professor of Osteopathic Manipulative Medicine at the Ohio University College of Osteopathic Medicine urges, "Whatever you do, don't give in to the urge to curl up in front of the fire and hibernate. Exercise is a lifetime commitment; give up the habit for only a week, and it's hard to get back into the swing; give it up for a six to eight weeks, and you're back to a couch potato level of fitness."

Some exercise-minded individuals use winter as an excuse to take up a new activity-cross country skiing, ice skating or snow shoeing. Devoted runners and walkers, of course, continue their regular routines throughout the year and may even prefer the winter workouts to the sweaty summer ones. When you're moving at a constant brisk pace, your body generates plenty of heat, and there's something nice about surveying the winter landscape while feeling a light sweat build inside your exercise clothes.

According to Eland, "Sometimes the hardest part is getting out the door! You may feel tempted to stretch longer than usual, and that's good," he said. "You should also consider warming up for a few minutes by running in place. Your muscles and joints are much more vulnerable to injury when they're cold."

Staying Warm

The key to staying warm is dressing in layers, preferably of lightweight, high-tech fabrics especially made for winter exercise.

The inner layer, made of polypropylene or a similar microfiber, should be breathable and able to wick moisture away from the skin. The middle layer should provide insulation, and synthetic fleece is ideal for this purpose. Many fleeces are waterproof as well, or at least quick drying to get rid of perspiration. The outer layer or shell should be as windproof and waterproof as possible.

"Dress so that you feel a bit cold for the first mile or so," advises Eland, "after that time, you'll feel 20 degrees warmer than the actual temperature. The advantage of dressing in layers is that you can strip the outer layers off if conditions change or you get too warm. Some fabrics can be compressed and stuffed into a fanny pack or pouch."

A hat is crucial since about 40 percent of body heat is lost through the head and neck. Gloves are also essential and, like the hat, should be made of breathable, water-resistant material.

Although hands and feet are farthest away from the heart and lacking insulating fat tissue, they also tend to sweat during exercise. It may be more important to have polypropylene glove and sock liners to wick the moisture than to have too much insulation.

Some studies, paradoxically, have found that during long exposures (an hour or more), too much insulation on the hands and feet can sometimes cause body temperature to drop and cause shivering.

"When it's very cold, it's important to keep skin covered," stresses Eland. "Wet skin exposed to a chilling wind can become frost bitten very quickly-in less than a minute, for example, when the wind chill is 25 degrees below zero Fahrenheit. Frost bite doesn't occur in temperatures above freezing, however, no matter how bitter the wind."

Although you may not realize that you're sweating, you're losing fluids during winter exercise. You need to get plenty to drink before going out and consume about eight ounces of water for every 15 minutes of exercise. Since outdoor water fountains are rarely operating in the winter months, it may be necessary to take along some water in your fanny pack.

Finally, it's important not to try to do too much. Consult your physician if you have any medical conditions or are over 50 before initiating an exercise program. If you are just returning to activity after several months off, start out with 10 to 20 minutes of moderate exercise, work up from there over a period of weeks to a month. An hour is probably long enough for a winter workout unless you're a seasoned veteran at cold weather activities. And observe some sensible limits: don't venture out when the temperature or chill factor is below zero or when visibility and traction are severely limited by snow and ice.

For those occasions-and for those who'd just rather not brave the elements-try some indoor workout options.

At a health club or Y, you can mix and match your exercise activities-30 minutes on a treadmill followed by 30 minutes on a stepper or exercise bike. Each machine works a different set of muscles, allowing you to work harder without fatiguing or overusing certain muscles.

"The kind of cross training that's possible at the health club will help you avoid injuries and it will also allow you to get regular exercise even when you are hobbled by an injury" said Eland. "With an injured foot, for example, you will probable be able to work out regularly on the rowing machine and even the exercise bike."

Any of these machines can be effective in building cardiovascular fitness and burning calories. Generally, at a "somewhat hard" pace, you'll burn about 700 calories an hour on a treadmill, 500 on an exercise bike and 600 on a rowing machine or stair stepper.

You can save money on membership fees by getting your own exercise equipment. The best bargains for nearly any kind of machine can be found at spring yard sales-which should give you a clue: don't invest in expensive equipment unless you have a lasting commitment.

Some studies do show, however, that persons with exercise equipment at home are more likely to maintain a regular exercise program than those who go to a health club or gym.

What you have at home depends on the space you have and the money you're willing to spend. Treadmills like those found at health centers may cost $20,000, but adequate home versions can be found for $300 to $700.

In addition to a treadmill, bike or stepper for aerobic conditioning, you should consider at least a few free weights or other strength training tools. Maintaining muscle mass and strength is just as important as cardiovascular conditioning, particularly for persons over age 50.

In the end, Eland advises that staying fit requires a varied, balanced program as well as a firm commitment to stay motivated, regardless of weather conditions.