Training in Extreme Temperatures

Performance may be influenced tremendously by temperature. As air temperature rises, the combination of environmental heat and increased body heat from exercise may result in bad effects ranging from decreased performance to death. Extreme cold, while usually not life threatening, can cause excessive body heat loss making good performance difficult.

The human body is able to maintain a fairly constant temperature under varying environmental conditions. To do this, it must be able to gain or lose heat. The core temperature is regulated to remain relatively constant, but the temperature of the shell, the skin and the tissues directly beneath it, varies directly with environmental conditions. The hypothalamus in the brain controls the body temperature and calls into play either heat loss or heat production mechanisms. Regulation comes in response to changes in the skin or blood temperature.

Normal metabolism in the body produces heat. Increased heat production can come from higher metabolic rates, disease, shivering or exercise. During exercise, the increased metabolic rate and energy production both generate heat. Most of the heat gain is due to the lack of efficiency of the body. It converts only 20-25% of energy produced into work; the rest is dissipated as heat.

Heat loss is governed by the following physical means:

Conduction: transfer of heat from the body by direct physical contact.
Convection: transfer of heat by movement of air or water over the body.
Radiation: radiation of heat from the body into space.
Evaporation: loss of heat by the body when converting sweat to vapor.

In a cold or cool environment, conduction and convection, along with some evaporation of sweat, can maintain the heat balance. As the temperature rises, evaporation of sweat becomes the main way of controlling the rise in core temperature. Evaporation can keep the body's exercising temperature in the normal range of 102-105 F under normal environmental circumstances.

Four environmental factors can interact to change the effectiveness of evaporation mechanism. They are air temperature, relative humidity, air movement, and radiation. Caution should be advised when the temperature is above 80 F or when the relative humidity exceeds 50-60%. A small breeze will help keep the body temperature near normal by helping to evaporate sweat. Radiant heat absorbed from the sun by the body will add to the heat load.

Heat Illnesses: (for you guys training in the Southern Hemisphere!)

Training unwisely under environmental heat stress may lead to a variety of heat illnesses which can be life threatening. These illnesses are caused by three factors: increased core temperature, loss of body fluids, and loss of electrolytes. While running or training in the heat, monitor your condition for signs of weakness, dizziness, nausea, disorientation, cessation of sweating and piloerection, the standing up of body hairs. If these signs occur, stop running and start the appropriate treatment. They could be symptoms of any of the major heat illnesses described below:

Heat Cramps: Salts can be lost in the sweat while running in the heat. If they are not replenished properly, muscle pain and cramps can occur. The body temperature does not become elevated. Prevention can come from heat acclimatization, ingestion of large amounts of water and by increasing the daily salt intake several days before the heat stress. Treatment is rest in a cool environment and replacement of lost salts.
Heat Exhaustion: Poor circulatory response to heat and reduction of blood volume due to increased sweating can lead to symptoms of general weakness, dizziness and nausea. The skin is usually cool and pale, but the person is probably still sweating. Body temperature is not elevated to dangerous levels (under 106F). Exercise must be stopped. Treat by rest in a cool environment, ingestion of cool liquids and cooling the body externally with water or ice.
Heat Stroke: When the body's temperature regulating system fails, excessively high body temperature and heat stroke can result. This is a serious condition which, if untreated, may well lead to death. It requires immediate medical attention. The symptoms are dry, warm and red skin, a reduction or loss of sweat and a body core temperature over 106F. Treatment is to immediately stop exercise, seek medical attention and start cooling the body with ice packs and cold water. The person may or may not be conscious. Cool liquids may be consumed if the person is conscious.

There are ways to reduce hazards when training in the heat and/or humidity, most are common sense:

Check the conditions before exercising and adjust your plan if needed. Slow the pace or decrease the duration of activity if training when hot or humid.
Run in the early morning or late evening to avoid the heat of the day. In many climates, late afternoon is the hottest time of the day and running then should be avoided.
Find a shady road or trail to run on.
Dress accordingly, wear as few clothes as you decently can. Try loose fitting white shorts and a white mesh top to reflect the heat and to permit evaporation. Protect your head from intense sun with a lightweight hat that can breathe. The back of the neck can be protected by the hat or a cotton kerchief. Ice can be wrapped in the kerchief and carried under the hat.
Drink fluids while running. Carry a water bottle or pick a route with water fountains. Drink 6-8 oz. of water for every 15-20 minutes of running. Also pour water over your head and chest.
Be aware of lost electrolytes if you've sweated excessively. Put an appropriate amount salt on foods and eat bananas and citrus fruit.
Avoid excess protein intake. Protein metabolism produces extra heat.
Know the signs and symptoms of heat illness and their treatments. If you have any of the symptoms, stop running, get to a cool place and consume cold fluids.

Fluid and Electrolyte Replacement

Optimal performance depends on proper hydration. Dehydration or excessive loss of body water reduces the amount of time you can exercise as well as necessitating slowing down. Changes that take place at the cellular level adversely effect muscle contraction. Water losses of 2% or more of body weight impair circulatory function and create heat imbalance.

Sweat is comprised mainly of water and sodium and chloride ions. These ions are known as electrolytes. Other electrolytes are also present in small amounts. Studies of electrolyte balance during and after exercise have shown increases in the electrolytes in the blood, but these changes are probably due to water loss and muscle use.

If running or training in the heat for several consecutive days, try to replace fluids and eat a balanced diet. Add salt to foods and select foods high in potassium such as bananas and citrus fruits. Salt tablets are unnecessary and may be harmful when not taken with adequate water.

Replacement Drinks

There has been no evidence to show that glucose-electrolyte solutions help replenish body water better than plain water. Electrolytes do not need replacing during exercise. After exercise, replenish as noted above. Glucose might be useful during exercise, but the concentration of the solution is very important and differs depending on the temperature. Too high a sugar concentration will retard absorption of water and too high electrolyte concentration tends to lead to intestinal cramps. If you plan to take any of these substances during a race, experiment during training before doing so. During high intensity prolonged exercise in the heat fluid replacement drinks:

Should contain less than 1.5 rounded teaspoons of sugar per quart.
Should contain little, if any, electrolytes.
Should be cold (40-50 F).

You should drink 6-8 ounces of fluid every 15-20 minutes during exercise. You can also hyperhydrate by drinking 2-4 cups of cold fluid 15-30 minutes before exercise.

Training in the Cold: (for you guys in the Northern Hemisphere)

Cold is usually not as hazardous as heat. With exercise metabolism, the body is able to maintain a constant core temperature in air temperatures as low as - 22F. This is regulated by internal mechanisms and not necessarily by the heat produced from exercise. Shivering can be seen during exercise when the core temperature is low. Under this stress, oxygen consumption is higher than when doing the same amount of exercise in warm weather.

Common sense tells you to be comfortable while training; this is also true in cold weather. Both body fat and clothing act as heat conserving mechanisms. High body fat is not conducive to good performance and is not common in (runners), so most must learn to dress warmly. Layers of clothing trap and warm air between them to act as insulation. If clothing becomes wet either through sweating or external sources (rain, snow), it can conduct heat away from the body. Fabrics that are waterproof, but can still breathe are best for external layers. Polypropylene is excellent next to the skin as it wicks away the water and allows a warm air layer to remain. A major part of heat loss is through the head, so wear a hat or ski headband to help keep warm. Gloves are nice as well. You can remove gloves, hat or layers of clothing as you become warmer. Training with bare legs in cold weather is not advised. The red color of the skin shows that a great deal of the blood is detoured to the skin trying to keep the body warm and is not going to the exercising muscles where it is needed most. Cold muscles feel tight and are more susceptible to injury, especially pulls and strains.

More info: http://www.runtheplanet.com/trainingracing/marathon/tempextreme.asp

Cold Weather Training Safety Tips

Falling temperatures and fewer daylight hours don't mean that your outdoor running/training routine has to go into hibernation for the winter. Running through the cold weather can help shake those winter blues, improve your energy level, and guarantee that you'll be in better shape once bathing suit season rolls around. Follow these tips to run safely and comfortably through wintry weather:

Watch for Frostbite. On really cold days, make sure you monitor your fingers, toes, ears, and nose. They may feel numb at first, but they should warm up a few minutes into your run. If you notice a patch of hard, pale, cold skin, you may have frostbite. Get out of the cold immediately and slowly warm the affected area. If numbness continues, seek emergency care.
Pay Attention to Temperature and Wind Chill. If the wind is strong, it penetrates your clothes and removes the insulating layer of warm air around you. Your movement also creates wind chill because it increases air movement past your body. If the temperature dips below zero or the wind chill is below minus 20, hit the treadmill instead.
Protect Your Hands and Feet. As much as 30% of your body heat escapes through your hands and feet. On mild days, wear gloves that wick moisture away. Mittens are a better choice on colder days because your fingers will share their body heat. You can also tuck disposable heat packets into your mittens. Add a wicking sock liner under a warm polar fleece or wool sock, but make sure you have enough room in your shoes to accommodate these thicker socks.
Dress in Layers. Start with a thin layer of synthetic material such as polypropylene, which wicks sweat from your body. Stay away from cotton because it holds the moisture and will keep you wet. An outer, breathable layer of nylon or Gore-Tex will help protect you against wind and precipitation, while still letting out heat and moisture to prevent overheating and chilling. If it's really cold out, you'll need a middle layer, such as polar fleece, for added insulation.
Check With Your MD. Cold air can trigger chest pain or asthma attacks in some people. Before braving the elements, talk to your doctor if you have any medical conditions or concerns about exercising outdoors.
Avoid Overdressing. You're going to warm up once you get moving, so you should feel a little bit chilly when you start your run. A good rule of thumb: Dress as if it's 20 degrees warmer outside than it really is.
Don't Forget Your Head. About 40% of your body heat is lost through your head. Wearing a hat will help prevent heat loss, so your circulatory system will have more heat to distribute to the rest of the body. When it's really cold, wear a face mask or a scarf over your mouth to warm the air you breathe and protect your face.
Get Some Shades. The glare from snow can cause snow blindness, so wear sunglasses (polarized lenses are best) to avoid this problem.
Don't Stay in Wet Clothes. If you get wet from rain, snow, or sweat in cold temperatures, you're at an increased risk for hypothermia, a lowering of your body temperature. If you're wet, change your clothes and get to warm shelter as quickly as possible. If you suspect hypothermia -- characterized by intense shivering, loss of coordination, slurred speech, and fatigue -- get emergency treatment immediately.
Stay Hydrated. Despite the cold weather, you'll still heat up and lose fluids through sweat. Cold air also has a drying effect, which can increase the risk of dehydration. Make sure you drink water or a sports drink before, during, and after your run.

More info: http://running.about.com/od/safetyweather/tp/coldweathersafety.htm

Anna Fisher
Healthwise Team Leader - Canada