Prevention of Cold Injuries during Exercise

John W. Castellani, Ph.D., FACSM; Andrew J. Young, Ph.D., FACSM; Michel B. Ducharme, Ph.D.; Gordon G. Giesbrecht, Ph.D.; Ellen Glickman, Ph.D., FACSM; Robert E. Sallis, M.D., FACSM

Disclosures

March 01, 2010

In This Article

Frostbite

Frostbite occurs when tissue temperatures fall below 0°C. The freezing point of skin is slightly below the freezing point of water due to the electrolyte content of the cells and extracellular fluid, with the skin surface reportedly freezing from −3.7 to −4.8°C.[30,129,192] Wet skin will cool faster,[129] will reach a lower temperature,[12] and will freeze at a higher threshold (~−0.6°C,[100]). Frostbite is most common in exposed skin (nose, ears, cheeks, exposed wrists), but also occurs in the hands and feet because peripheral vasoconstriction significantly lowers tissue temperatures.[33] Instantaneous frostbite can occur when the skin comes in contact with supercooled liquids, such as petroleum products, oil, fuel, antifreeze, and alcohol, all of which remain liquid at temperatures of −40°C. Contact frostbite can occur by touching cold objects with bare skin (particularly highly conductive metal or stone), which causes rapid heat loss.

Usually, the first sign of frostbite is numbness. In the periphery, the initial sense of cooling begins at skin temperatures of 28°C (~82°F;[81] and pain appears at ~ 20°C (68°F;,[42,81] but as skin temperature falls below 10°C (50°F) these sensations are replaced by numbness.[144] Individuals often report feeling a "wooden" sensation in the injured area. After rewarming, pain is significant. The initial sensations are an uncomfortable sense of cold, which may include tingling, burning, aching, sharp pain, and decreased sensation.[128] The skin color may initially appear red; it then becomes waxy white. Note that peripheral temperatures (hands, feet) may be indicative of a generalized whole body cooling that may ultimately result in hypothermia. Body heat content has been found to be directly related to the skin temperature of fingers and toes.[14]

Table 5 presents the predisposing factors for frostbite. Risk factors are separated by cause including environmental, mechanical, physiological, and psychological. For the relatively healthy athlete, the most relevant are the environmental and mechanical factors since these can be prevented through recognition and employing appropriate countermeasures. Important risk factors that cannot be changed include sex and race. Peripheral responses to cold appear to differ between men and women. During exposure of the hand to cold while the rest of the body remains warm, finger temperatures are typically lower in women than men.[76,142,147] Contact cooling studies suggest that women's fingers cool faster than men, possibly due to hand size.[91] Prevalence of peripheral vascular disorders like Raynaud's phenomenon is also higher in women, which may also make them more susceptible to peripheral cold injury.[70] Raynaud's phenomenon (RP) is a transient, vasospastic disorder that causes blood vessels to constrict to a greater extent than normal when exposed to the cold leading to very low blood flow to the digits.[190] The affected area first turns white, blue if the area becomes cyanotic and finally red upon rewarming. RP is associated with tingling, swelling, or painful throbbing. Individuals with scleroderma, lupus or arthritis are more likely to suffer from RP as are individuals who live in cold-weather regions.[11] Black men and women are 2-4 times more likely to suffer a cold weather injury than their Caucasian counterparts.[33] Early information on frostbite risk due to race was conducted in military populations and observed higher frostbite rates in blacks[17,172] and a recent epidemiological study[33] controlling for occupational exposure to cold also observed a higher risk for blacks across many different job descriptions. Physiological and anthropometric reasons suggested for the higher frostbite risk in African-Americans include less pronounced CIVD, increased sympathetic response to cold exposure, and thinner, longer digits.[17]

In most cases, sojourning to high altitude is synonymous with cold exposure. The air temperature decreases 2°C with every 310 m (1000 ft) above the site at which the temperature was measured. Also, the wind chill temperature will be lower at higher altitudes due to the combination of lower air temperatures and higher wind speeds caused by less tree cover. Epidemiological evidence suggests that the risk of frostbite significantly increases above 5182 m.[77] The combination of the known cognitive deficits elicited by hypoxia[5] and preliminary data suggesting that cutaneous sensitivity to cold is blunted in the toes[65] can potentially lead to poor behavioral choices at high altitude and increase individual susceptibility to cold injury. Physiologically, CIVD responses appear to be blunted by altitude exposures (> 4350 m) in nonaltitude acclimatized subjects,[28,122,171] with possibly some restoration of responses after altitude acclimatization of at least 21-45 d.[28,122] Altitude exposure (> 8000 ft) also decreases the shivering and vasoconstrictor response to cold exposure.[10,92]

Prevention Strategies for Frostbite

Wind Chill

The principal cold-stress determinants during outdoor activities in cold weather are air temperature, wind speed, and wetness. Most body heat loss during cold exposure occurs through radiation, conduction, and convection, so when ambient temperatures are colder than body temperatures, the thermal gradient favors body heat loss.[67] Wind exacerbates heat loss by facilitating convective heat loss[54] and reduces the insulative value of clothing. The wind chill temperature (WCT) index (Fig. 3) integrates wind speed and air temperature to provide an estimate of the cooling power of the environment.[130,138] The WCT standardizes the cooling power of the environment to an equivalent air temperature for calm conditions.

Figure 3.

Wind chill temperature index in Fahrenheit and Celsius. Frostbite times are for exposed facial skin. Top chart is from the U.S. National Weather Service; bottom chart is from the Meteorological Society of Canada/Environment Canada.

WCTs are specific in their correct application, only estimating the danger of cooling for the exposed skin of persons walking at 1.3 m·s−1 (3 mph). Wind does not cause an exposed object to become cooler than the ambient temperature, but instead wind causes exposed objects to cool toward ambient temperature more rapidly than without wind. Wind speeds obtained from weather reports do not take into account man-made wind. For example, running and skiing produce wind across the body at the same rate as the body is moving. The WCT presents the relative risk of frostbite and the predicted times to freezing (Fig. 3) of exposed facial skin.[38] Facial skin was chosen because this area of the body is typically not protected. Frostbite cannot occur if the air temperature is above 0°C (32°F). Wet skin exposed to the wind will cool even faster and if the skin is wet and exposed to wind, the ambient temperature used for the WCT table should be 10°C lower than the actual ambient temperature.[12] Also, the local weather may vary greatly depending on the local topography. Wind speeds are also measured at ~ 10 m and the actual exposure of someone varies with trees, buildings and the direction you are facing. Compared to lower elevations, wind speeds are generally greater at high altitudes, where there is little tree cover. Evidence Statement. The risk of frostbite is less than 5% when the ambient temperature is above −15°C (5°F), but increased safety surveillance of exercisers is warranted when the WCT falls below −27°C (−18°F) since, in those conditions, frostbite can occur in 30 min or less in exposed skin. Category C

Exercise

Physical activity is an effective countermeasure to increase finger skin temperature when there is no wind. For example, at rest in −10°C air with no wind, the gloved finger temperature is ~ 18°C. As metabolic heat production increases 2-4 fold, finger temperature rises to 22-27°C.[118] However, if conditions are windy, physical activity does not significantly alter the temperature of exposed or covered fingers. Exposure to a 5 m·s−1 (11 mph) wind at an ambient temperature of −10°C when performing light to moderate physical activity only raises the finger temperature in a glove from 10°C at rest to ~13°C. However, increasing the exercise intensity from 220 to 350 W (2.2-3.5 METs) increases nose temperatures from 4.5°C to 8.9°C, even in a 5 m·s−1 wind[12,58] and Brajkovic and Ducharme[10] found that nose skin temperature rose from 9.7°C at rest to 18.1°C during exercise.

Clothing

The same clothing principles of layering and staying dry are also used for gloves/mittens, socks, and hats. Gloves and hats can be used to regulate heat loss for each individual by adding or removing particular items based on individual subjective thermal sensations. Gloves and mittens should be donned before the hands become cold. Then as the work intensity increases and the hands become warm, gloves can be removed so that sweat does not accumulate in the fabric. Using mittens, compared to gloves, will provide greater protection from cold injuries. However, this protection must be weighed against the significant decline in manual dexterity that occurs with mitten use. Liner gloves can be used to keep moisture away from skin, allow for dexterity with protection, and add a layer of insulation. Individuals should not blow warm breath into mittens or gloves because it can cause the hands to become even colder due to the vapor from the breath adding moisture to the glove that may freeze and contribute to further cooling.

Spreading petroleum jelly or other emollients onto the skin does not lower the risk of frostbite;[111,175] indeed the use of these products may increase the relative risk of frostbite on the head.[110] Using white petroleum jelly may increase risk by giving a false sense of security because subjects perceive the skin to be warmer, compared to using no petroleum jelly, when the face is exposed to the cold.[111] These products should not be used in freezing weather. Straps on gloves and other equipment should not be pulled too tight and shoelaces should not be tied too tightly. Backpack straps may decrease blood flow to the arms and hands, so dropping the load every few hours may be needed to allow increased circulation. Buddy checks can be implemented at this time.

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