January 22, 2001


What should I wear to stay warm on a winter run?

How does the body lose heat? I have heard of two ways: Convection and conduction. Are there others? And how should I apply this information when I am choosing what to wear on a winter run?

— Edward Johnson New York, New York

Say, this would be a good question for "Who Wants To Be A Millionaire — the Outside Edition." Get the wrong answer, you not only don't get a million bucks, you get dunked in a tub full of ice water.

Anyway, you'd be off to a good start. Convection and conduction are indeed two key ways in which the body loses heat. Convection is the process by which heat is transferred from our bodies in a gas or liquid. When running, you're apt to lose a fair amount of heat by this process because your body movement and arm swings will cause a substantial "bellows effect," pumping warmed air out from under your clothing. Conduction is heat loss by transfer from one substance to another. Runners don't have to worry too much about this unless it's windy, but bicyclists have to dress carefully to ensure that air moving past them at 15 to 20 miles per hour doesn't grab too much heat.

There are three other ways the body loses heat. Radiation is one; if it's very cold and you're not well insulated, your body will radiate heat and cool down. That can happen just by sitting around—it's why we wear clothes in the first place. There are two others: Respiration and evaporation, both of which could have a big impact on a runner. Respiration heat loss occurs simply by breathing. When you suck in a big lung full of cold, dry air, your body has to warm it and moisturize it. That takes a hell of a lot of energy; if you're simply sitting still at 0 degrees, you lose nearly half of your energy output to respiration. And as a runner, you're of course breathing hard and often. A mask made of foam may offer some help here, although you may find it a bit uncomfortable to wear.

Evaporative heat loss is largely caused by sweating. Even on a cold day you probably sweat, and as you sweat your body heats it to the point that it evaporates. This drains a tremendous amount of energy from your system. To keep it to a minimum, keep well covered but don't over-heat. The less sweating you do, the better.

I used to run a lot in temperatures at or below freezing, and usually wore a midweight nylon/Spandex tights and a zip-top lightweight Capilene turtleneck, or one made of similar material (polyester-based fabrics are by far the best because the transport moisture from your skin quickly and absorb little moisture themselves). The zipper turtleneck gave me good temp control; on colder days I'd wear a T-shirt under made of Coolmax or similar material. You might also wear some sort of light jacket, such as Pearl Izumi's Pursuit jacket ($80), or an L.L. Bean Ridge Runner ($79). I'd also be sure to wear a hat -— just a light cycling cap probably is fine — and light gloves. My feet typically didn't get cold, but these days I'd probably go for a shoe with a Gore-Tex liner, such as Montrail's Hurricane Ridge GTX ($115) and a pair of SmartWool socks ($8).

How to know what works? Put it this way, if you spend a half-hour in a hot shower trying to warm up when you get home, you need to adjust your clothing.