2. A drop in core temperature induced thermogenesis. A drop in core temperature initiates:

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1 Get Adobe Flash player Introduction to Cold: Only in rare instances do people exercise at very low body temperatures (Brooks, 2009). Due to the combination of increased metabolism duirng exercise and the ability to wear extra clothing, the risk of hyperthermia while exercising is low. However, cold climates can contribute to decrements in physical performance and can cause serious injury during extreme exposure if the body is not acclimatized. Acute Responses to Exercise in the Cold: Several studies have been conducted on exercise in cold exposure. All of these studies reported similar limitations that may have affected the results, including the following: duration and intensity of exercise in cold, time spent in cold before exercise, clothing, degree of acclimation, and shivering. Below is a summary of findings from studies looking at acute adaptations and responses to submax exercise in cold: 1. VO 2 levels increased during exercise. VO 2max levels were unaffected by cold exposure (Galloway and Maughan, 1997; Patton and Vogel, 1994) 2. A drop in core temperature induced thermogenesis. A drop in core temperature initiates: -increased muscle tone, shivering, increased resting metabolism by 2-3x, increased fat utilization by up to 63%, increased CHO utilization by up to 588%. The relative contribution of fat compared to CHO actually decreases. (Shephard, 1993; Brooks and Mercier, 1994) 3. Effects on strength: Strength decreased due to impaired enzymatic activity. Those who exercise in the cold fatigue faster because of increased motor unit recruitment and decreased blood flow. 4. Exercise in the cold did not enhance fat metabolism (Sink et al., 2009; Shephard, 1993). Studies show controversial findings on fat utilization. Some studies found that exercising in the cold increases fat utilization while other studies found that fat utilization was unaffected (Kruk et al., 1991; Shephard, 1993). -Initial fat values influence the rate at which fat is used during exercise. -If cold exposure is severe enough to lower core temperature, then lipid utilization will increase (Hurley and Haymes, 1982), but CHO usage will increase so much more that the relative contribution of fat energy decreases 5. Shivering: Lactate production increases in shivering muscles. Peripheral vasoconstriction in cold temperatures helps to keeps internal organs warm, but also reduces skeletal muscle blood flow. Reduced blood flow results in a reduced ability to remove lactate from the shivering muscles (Shephard, 1993). Peripheral vasoconstriction also increases central blood volume and blood pressure (González-Alonso et al., 2008). 1

2 6. Pre-exercise cold exposure: Subjects that were exposed to cold temperatures minutes prior to beginning exercise showed that pre-exercise exposure had the following effects: Induced shivering and elevated CHO utilization during exercise, lower muscle temperatures and delayed warming of muscle (causing reduced mechanical efficiency), and recruitment of more fast-twitch fibers (Jentjens et al., 2001) 7. Exercise in severly cold temperatures yielded reduced glycogenolysis due to lower muscle temperatures and reduced sympathetic nervous system responses. Lipid utilization increased in order to maintain core temperature via thermogenesis and supply the CNS with glucose (Jentjens et al., 2001; Brooks, 2005). Get Adobe Flash player Figure 1: Summary of the effect of cold climate on exercise (Brooks, 2005; Galloway and Maughan, 1997; Jentjens et al., 2001; Shephard, 1993). 2

3 Acclimatization to Exercise in the Cold Intro: Three major adaptations occur in individuals who are adapted to the cold: increase shivering threshold, increased hand and feet temperature, and increased ability to sleep. Shivering: Individuals who are acclimated to the cold are able to maintain heat production, and therefore, shiver less than non-acclimated individuals. Shivering acclimation in humans is supported Oksa (2009) who found shivering occurs later in subjects exposed to three weeks of cold temperatures. The mechanism for shivering acclimation may be caused by secretion of thyroid hormones and their tissues becoming more sensitive to norepinephrine, which causes uncoupled oxidative phosphorylation (release of heat without ATP production). As a result, peripheral blood vessels possess an increased ability to vasodilate, which decreases the the mean skin temperature at which shivering begins (Weber, 2005). That is, individuals who are acclimated to the cold begin shivering at lower skin temperatures. Additionally, chronic exposure to cold may increase the thickness of subcutaneous fat (Brooks, 2005). However, the mechanism supporting the change is unknown. The increase in subcutaneous fat would help maintain body temperature by causing an earlier onset and greater magnitude of shivering (Tikuisis et al, 1991). Hand and Feet Temperature: Hand and feet temperatures significantly decrease is unacclimated individuals during cold exposure. In contrast, acclimated people maintain approximately normal hand and feet temperatures (Brookes, 2005). The mechanism responsible for the acclimatization is the improved intermittent peripheral vasodilation in the hands and feet. Adaptations in the hands and feet are particularly important for exercises or sports that rely on dexterity during performance (i.e. baseball, football). Sleep Ability: Unacclimated people will shiver too much to sleep. The ability to sleep in the cold is dependent on the extent of nonshivering thermogenesis as a result of increased secretion of norepinephrine (see Shivering above to learn more about this mechanism). The positive relationship between sleep and nonshivering thermogenesis in cold environments is supported by Pandolf (1979) who found people placed in a cold chamber acclimated and therefore, slept better in cold conditions after one week. Cold Injuries Cold injuries occur with low temperatures, wind chill, prolonged exercise, and improper clothing (Cuppett 2012). Individuals at risk for cold injuries, such as hypothermia and frostbite, occur when an individual is exposed to temperatures typically below 0⁰C, wind chill, water tempature (Bergeron 2012, Cappaert 2008). 3

4 Individuals at risk for cold injuries have the following characteristics: lean body mass, female, illness, exposed skin, and improper clothing (Cuppett 2012, Tloughan 2011) Figure 2: Wind Chill is calculated by wind speed and temperature( Hypothermia: Hypothermia is the depression of the central nervous system resulting in sleep, inability to shiver, and eventually a coma. Hypothermia occurs in exercise the rate of heat production exceeds the heat of heat loss (Brooks 2005, Cuppett 2012). Hypothermia may be classified in four categories in which the core temperature is below 35⁰C. Mild is classified as a core temp of 35-37⁰C, moderate 32-34⁰C, and severe below 32⁰C (Cappaert 2008) The physiological changes of hypothermia includes glycogen depletion from the body due to the body trying to keep itself warm. Depletion of glycogen can lead to hypoglycemia and reduced CNS function(cappaert 2008, Cuppett 2012). Hypoglycemia decreases shivering which increases hypothermia (Castellani 2006). Treatment of hypothermia is to remove all wet clothing, passively warm via adding clothing or blankets, room temp 21-24⁰C, and if hospitalized intravenous fluid (Dhar 2000). 4

5 Figure 3. Signs and symptoms of cold injuries. (Cappaert 2008) Frostbite: 5

6 Frostbite is the result of vasoconstriction in response to cold that results frozen tissue, tends to be the extremities. Long term injury may result in circulator damage or gangrene and result in loss of extremity. Risk factors temperature, wind chill, fatigue, circulatory impairment, improper clothing, high elevation, alcohol consumption, and tobacco use (Cuppett 2012, Brooks 2005). Frost bite occurs at temperatures from 0⁰C to -35C and below (Bergeron 2012). There are four grades of frostbite. First degree (frost nip) symptoms swelling, numbness, pain (Cuppett 2012). Notice the image below how the right hand is swollen compared to the left. 6

7 Figure 4. First degree frostbite. ( Second degree symptoms swelling, redness, blister formation (Cuppett 2012). 7

8 Figure 5. Second degree frostbite. Get Adobe Flash player 8

9 Third degree symptoms full thickness destruction of skin, blisters and hardened wax like skinn (Cuppett 2012). 9

10 Figure 6. Third degree frostbite. Fourth degree symptoms are the loss of entire extremity (bone, muscle, tendon) redness, edema, ashy skin, numbness tingling, burning (Cuppett 2012). 10

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12 Figure 7. Fourth degreee frostbite. 12

13 Physiological changes of frostbite includes vasoconstriction to bring the body s blood supply to the trunk (Brooks 2005, Cuppett 2012). Vasoconstriction occurs when the skin s temperature is less than 35⁰C and 31⁰C in water (Castellani 2006). The limited blood flow to extremities allows for the cells to freeze. Cellular damage is due to electrolyte and water concentration freezing (Tloughan 2011). The treatment for frostbite is to remove the individual from cold exposure, passively rewarm tissue, rehydration, and restore circulation (Cuppett 2012). Cold injury prevalence, performance effects, and prevention: Exercise Performance in the Cold Prevalence of hypothermia and frostbite occur mainly in outdoor winter sports, occasionally hypothermia and frostbite are seen in outdoor fall sports like soccer, football, cross country, and lacrosse. 3% to 5% of all injuries in mountaineers and 20% of all injuries in Nordic skiers reported were due to hypothermia or frostbite (Sallis 1999). The CDC found on average 689 deaths per year are due to hypothermia (CDC 2013). One study found in % of mountaineers got 1 st degree frostbite, hands (26.4%) and feet (24.1%) involvement were most common(harirchi 2005). Hypothermia and frostbite are serious cold injuries, they can prevent individuals from competing, loss of extremities, and death. Hypothermic conditions slows recovery time of potential contractile properties of muscles (Drinkwater 2007). Prevention of cold injures such as hypothermia and frost bite include different types of clothing and acclimatization. Clothing that keeps the individual warm and acts as a wind breaker are suggested. One study in 2012 by Burtscher et al found that walking 1 hour at 0⁰C and a wind speed of 10 the more clothed an individual is the greater prevention of hypothermia there is.moderate exercise in cold environments helps individuals feel warmer and relives pain after 90 minutes of immobility briefly (Muller 2011).Cold induced vasodilatation is a hypothesized protective mechanism. Cold induced vasodilatation occurs in the toes during exercise and increases core temp (Dobnikar 2009). 13

14 Figure 8. Clothing combinations for insulation. 14