Don't let winter chill your training.

Cold weather requires a little extra planning and protection before you shoot out the door. Your body loses heat quickly in cold weather due to convection (heat loss due to motion), conduction (transfer of heat due to temperature gradients), evaporation of moisture, and radiation (transfer of energy caused by the difference between skin temperature and ambient temperature). The right layers will protect you from the elements without discomfort and without weighing you down. While hypothermia-related deaths are relatively rare, the cold can take its toll on your performance and comfort, and frostbitten skin is always a risk. Take precautions and you can maintain your mileage despite winter weather.

The challenge in dressing for winter weather is not only to keep the winter chill and wetness out, but to handle the heat and moisture your body produces as well. Even in subfreezing temperatures your body produces a lot of heat and sweat--up to two liters per hour when running. Water conducts heat away from your body 25 times faster than air--a very handy fact in the summer when sweat helps to keep you from overheating, but dangerous in cold temperatures. Staying dry under your layers is critical and can impact heart rate, ratings of perceived exertion, as well as comfort, dryness and warmth.

First Layer--Skip the cotton skivvies. Cotton holds moisture next to your skin--just what you don't want when the wind chill factor dips. Choose the new lightweight, moisture-wicking fabrics that hold only a tiny percent of their weight in moisture. Modern performance microfibers hold less than one percent of their weight in water versus 17% for wool, 8% for cotton, and 5% for silk. Read fabric labels, and price tags--you will have to pay for the new high-tech microfibers that promise to shun wetness.

Second Layer--If you are planning to run in really cold weather, you may need a middle layer to trap the warmth your muscles generate. Pick fleece for maximum warmth and minimum bulk. Fleece also has the advantage of staying drier than natural fibers. Even among fleece fabrics, research has produced lighter and drier products. Most labels will state their specifications. Compare facts and prices.

Top Layer-- Technological advances have given runners another great gift with fabrics that block the elements (rain, snow, and wind) without trapping too much heat and moisture underneath. Look for waterproof fabrics that vent, but be prepared to pay a hefty price. If you live in cold regions and refuse to let winter weather keep you in, then it is worth the investment. Otherwise nylon blends with vent flaps at the back should be adequate.

Hands and Head--When your mom told you to put on a hat because you lose a lot of heat from up top, she was right. Up to 40% of your body's heat loss occurs from the head due to a large blood supply, extra surface area, and the mucus membranes of the nose and mouth. Don't neglect your head or your hands, which can be very vulnerable to the elements. Look for thin fleece hats and lightweight glove liners for your hands.

Feet--Cotton is a poor choice for socks as well as underwear. Look for synthetic socks that won't hold moisture and become packed down when damp. And, most standard running shoes are designed to perform their best in moderate temperatures. They are designed for maximum ventilation, traction on dry surfaces, and cushioning that may be less resilient in cold temperatures. If you run outdoors throughout 4 the winter, consider investing in shoes better designed to handle the elements.

Don't overdo it--Choose a minimum amount of clothing to keep you comfortable. Remember that even brisk walking will generate a lot of heat. Traditional advice suggests that you should feel a little chilled when you first step out. Experience will improve your judgment, so don't take a long run before you know what works best for you.

(Medicine and Science in Sports and Exercise, 1999, Vol. 31, No. 10, pp.1367-1373; Journal of Orthopaedic and Sports Physical Therapy, 1995, Vol. 21, No. 3, pp. 158-171; Journal of the American Medical Society, 2000, Vol. 283, No. 7, pp. 11-14; East Carolina University's Human Performance Laboratory Data on Thermolite Microfiber fabrics; Consumer Reports on Health, January, 1999)