Cold weather is an subjective expression that may convey different meanings to different people. In an equatorial country, any temperature below 60°F (15.5°C) is often characterized as cold; in high northern latitudes, cold weather is said to exist when the temperature is persistently in the range of ™20°F (™28°C) or colder. Like extreme heat, the human body possesses the ability to adapt itself to the stresses created by cold.
From a meteorological perspective, cold weather is generally said to exist where the air temperature is 40°F (4°C), or below. Accompanying climatic conditions such as snow, ice, and wind will increase the effect of cold temperatures on human performance. The prevalent wind chill factor, the correlation between temperature and wind velocity, is the most important of these factors, as increased wind velocity will increase the effect of cold upon the body. Sports such as speed skating, running, cross-country skiing, and cold weather cycling are of special note in assessing wind chill, because each activity, by virtue of the athlete's movement, will generate its own wind forces.
Cold weather affects the bodily systems in different ways. The cardiovascular system, the heart-connected network of vessels that distributes blood throughout the body, responds to cold stimulus by increasing blood pressure and heart rate, and reducing the amount of blood closest to the skin surface. The airway passages of the cardiorespiratory system, which governs the breathing mechanisms, tend to narrow, making the inhalation of air more difficult. Persons who are susceptible to asthma or exercise-induced bronchitis have greater difficulty breathing in cold air. The bodily stores of glucose, stored as glycogen in the liver and muscles and converted to the energy component adenosine triphosphate (ATP), are depleted approximately five times more quickly in cold weather, a circumstance that forces the body to switch to the conversion of body fat to ATP for its energy requirements.
In addition to the effect of cold weather upon the body systems, cold weather creates unique injury hazards. Hypothermia and frostbite are the two chief cold weather injuries. Frostbite is the freezing of a portion of skin or bodily tissue through exposure to cold. Hypothermia is the reduction of the core temperature of the body from its healthy, steady state of 98.6°F (37°C) to below 95°F (35°C). In this condition, the body cannot generate sufficient heat through metabolism to keep itself warm. The hypothalamus gland, which regulates temperature, ceases to function; if the hypothermia is not treated quickly, death may result.
As serious as the consequences of cold weather injury can be, the precautions available to the cold weather athlete are both straightforward and effective. One of the most important steps to be taken for cold weather athletics wearing clothing that is
In addition, water or an electrolytic fluid should be carried; dehydration is as significant a concern in the winter cold as it presents in summer heat, as a dehydrated cold weather athlete will have a correspondingly reduced blood volume. The consumption of alcohol and cold weather exercise should be avoided, as alcohol is a diuretic that tends to dehydrate the body.
A thorough warm up and cool down of the body are essential to cold weather exercise. The warm up will lessen both the mental and the physiological shock of taking the body into cold.
Finally, route planning is important to minimize wind chill effects for endurance sports such as running and cross-country skiing. The athlete should begin the workout by heading into the wind; in this fashion, the perspiration generated on the body will not be subject to wind chill effect on the return portion of the training.