By Daniel G. Graetzer, Ph.D.
Faculty Member, School of Health Sciences
Note: This article is part 2 of a two-part series on outdoor winter sports, physiology and exercise clothing.
Aerodynamically-designed clothing is of great importance to athletes who compete in speed-related winter sports such as downhill skiing and speed skating. The speeds that athletes reach in these sports make wind resistance the major restricting force to athletic performance.
Bicycling tests in wind tunnels have shown that wearing tight, smooth clothing creates a reduction in aerodynamic drag. That reduction in drag makes the difference between winning an Olympic medal and being forgotten forever. Tight, smooth and lightweight clothing has now become standard in speed sports because the friction arising from contact with air is minimized, reducing aerodynamic drag.
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The Role of ‘Clo’ in Winter Sports Exercise Clothing
Metabolic heat production during exercise creates an air pocket “micro-climate” between skin and the clothing that insulates the body. Scientists quantify the insulating effect of clothing in “Clo” units.
One Clo will maintain the comfort of a resting person with a metabolic rate of 50 Kcal/meter squared/hour at a normal air temperature of 70 degrees Fahrenheit. A relative humidity (the percentage of moisture saturation of ambient air) of less than 50% and a moderate air circulation (wind chill) of 20 feet per minute (6 meters per minute) is assumed in this situation.
As weather conditions get colder, warmer clothing with a higher Clo index is needed for both safety and performance. As body heat increases via exercise-induced metabolism, the Clo value required to maintain your comfort decreases.
For example, someone who is winter camping in the mountains generally needs protective clothing of about 10 Clo units. When you’re hiking in cold weather, you only need clothing with a rating of just three Clo because body heat production while walking is three to four times greater than sleeping in a tent in cold weather.
Research has shown that the insulating value of exercise clothing in moderately cold weather during winter sports such as competitive Nordic skiing or speed skating should be about 1.6 Clo. That allows the micro-climate between your skin and clothing to remain at a comfortable 70-75 degrees Fahrenheit.
Air Provides the True Insulation in Winter Clothing
The insulation of all clothing materials is directly related to the amount of air trapped within the material itself, which is why there is a “loft” rating for down products. The type of fiber used is of minimal importance as heated air is the primary factor determining the level of insulation. Four materials commonly used as middle-layer exercise clothing – goose down, wool, polyester and polyolefin – show no thermal insulator superiority of any synthetic fiber over natural fibers.
Regardless of advertiser claims, no fabric or material has been shown to provide notably higher insulation against cold. Air is the true insulator; the function of filling material is just to immobilize enclosed air, prevent convection currents and retain heat within the middle layer.
While stylish, elegant uniforms may have looked attractive in the past, they can cause premature exhaustion due to high heat storage as well as premature heat exhaustion on a cold day. Years ago, baseball players took to the field wearing baggy wool uniforms, and Wimbledon tennis tournaments saw men competing in full-length twill pants and women in knee-length skirts.
Today, the athletic clothing industry emphasizes biophysics technology over fashion. Annual sales of athletic clothing are in the billions of dollars, following the recognition that wearing proper sport-specific clothing assists in improving aerodynamics, body temperature control, more freedom of movement and protection from cold-related injuries. Recent advances in the biotechnological design of exercise clothing for cold weather has enhanced people’s safety, comfort and enjoyment of outdoor sports.
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