QUESTION: Is it possible to dress warmly enough to exercise outdoors even when the weather turns extremely cold? I appreciate your articles on indoor exercise but don't like to exercise indoors.

ANSWER: I exercise outdoors most of the year, but when it gets really cold, I usually find something to do indoors because I really don't care that much where I work out.However, it is possible to work outdoors even when it is extremely cold if you use the proper clothing material. The problem relates to the production of sweat during work. If the sweat accumulates in the material next to your skin, the insulation properties of that material are decreased and you will get cold. I will discuss a few ideas presented in an article from the December issue of Running & Fitnews (American Running and Fitness Association) regarding clothing for winter workouts.

First, it is important to realize that the insulative property of clothing is related to the amount of air trapped in the fabric. How much air depends on the size and shape of the individual fibers that make up the fabric. When fabrics become wet, some of the air space is displaced by the water and the insulating power is lost. At rest, most fabrics work OK because there is little sweat production, so the small amount of water vapor produced by the skin can get to the surface and be released without building up next to the skin.

With exercise, releasing water becomes a problem because the body begins to sweat to cool itself. The goal in this situation is to be sure the inner layer of clothing stays dry. Most experts recommend an inner layer of either fishnet or mesh construction with fibers that do not absorb water. Cotton is a great material for many situations, but when you sweat, the microscopically ribbon-shaped fibers just swell and sag, wet and limp, against the skin. A better choice for this inner layer is polypropylene, Capilene or Thermax. These fibers act much like a lantern wick (which draws up kerosene because the fibers don't absorb the the liquid), allowing the moisture produced by sweating to be drawn up away from the skin to the outer layers where it can evaporate.

Once you have the proper material next to your skin, you simply layer additional clothing (to increase the amount of air trapped between layers) to the extent necessary based on the temperature. Another advantage of layering is that you can remove a layer (and tie it around your waist) if you get too warm. It is probably best to be slightly chilled when you start out so that you will warm up to a comfortable temperature in 10 to 15 minutes as your body produces more heat. With skiing or other activities that produce a little less heat, you need to wear enough layers to be comfortable right from the start.

Be sure to protect your head. Wise old outdoor enthusiasts say, "When your feet are cold put on a hat," because you can lose so much heat from your head. Hands are also a critical area. If it is really cold, wear mittens rather than gloves.

Dressing properly can really influence how much you enjoy activity in the out-of-doors.

- Garth Fisher is director of the Human Performance Research Center at Brigham Young University.