Concerns for Fluid Replacement and Outdoor Exercising

We walk, run, play or compete in nearly all temperatures. Because of this we must be aware of the dangers of being too hot or too cold. We must also recognize the importance of replacing our body fluids before, during and after our workouts.

Heat

Excess heat not only negatively affects our performance, but it also can be a source of serious health problems. As the outside temperature increases it becomes less and less possible to get rid of the body heat exercise produces. For example, if exercising at 37 degrees Fahrenheit (3 degrees Celcius) you are 20% more effective in eliminating body heat than if you are exercising at 67 degrees F (20 degrees C) and 150% more effective than if you are exercising at 104 degrees Fahrenheit (40 degrees C). It is not uncommon for the body to reach a temperature of 104 to 106 degrees F (40 to 41 degrees C) when exercising. But normal resting body temperature is 98.6 degrees F (37 degrees C). The high heat makes it difficult, or impossible, for the perspiration to evaporate, so the body can't be effectively cooled.

The heat generated in the muscles is released by:

• Conduction-from the warmer muscles to the cooler skin.
• Convection-from the heat loss from the skin to the air.
• Evaporation-the perspiration being vaporized.

Conduction occurs through the body's liquids, such as the blood, absorbing the heat created by the contraction of the muscles and moving it to the cooler skin. Water can absorb many thousands of times more heat than the air can, so it is an excellent conductor of heat from the muscles.

Convection occurs when the heat near the skin is absorbed into the atmosphere. For a swimmer in a cool pool, effective convection is very easy. For the runner it is more difficult. It is aided by a lower air temperature and by wind. A four mile an hour wind is twice as effective in cooling as is a one mile an hour wind. (This is the basis for the wind chill factor associated with winds in cool environments.)

Evaporation is the most effective method for cooling a body that is exercising in the air. Each liter of sweat that evaporates takes with it 580 kilocalories. This is enough heat to raise the temperature of 10 liters of water 58 degrees C (101/2 quarts of water to 105 degrees F). As the skin is cooled by the evaporation of the sweat, the skin is able to take more of the heat from the blood and thereby cool the blood so that it can pick up more heat from the muscles. The humidity is the most important factor regulating the evaporation of one's sweat.

High humidity reduces the ability of your perspiration to be evaporated. It is the evaporation of the sweat that produces the cooling effect as the perspiration goes from liquid to gas. This amounts to a cooling effect of over a half a kilocalorie per gram of perspiration evaporated. Exercising in a rubber suit has similar effects to high humidity because the water cannot evaporate - it is not recommended.

Wind has the opposite effect. It affects the body temperature by cooling it faster than the registered temperature would warrant. We have all heard of the wind chill factor present on colder days. The wind makes the body experience more cold than would be expected by the actual temperature. (See chart.) But even on warmer days the wind will evaporate the perspiration and cool the body faster than might otherwise be expected. This may increase the need for fluids to continue the production of sweat.

Influence of the Menstrual Cycle

During the luteal phase (after ovulation) of the cycle, during moderate exercise, females' body temperature and heart rate tend to raise significantly. (1) Blood volume (plasma volume) seems to decrease during the follicular cycle (after menstrual flow). (2)

 

Fluid Replacement

The hyperthermia (high temperature) developed during exercise, particularly when the sweat cannot evaporate, is a major cause of fatigue. This is particularly true when the body has lost 2% of its water through perspiration. Since it is not uncommon to lose 1-5 liters of water when exercising it is not difficult to enter the stage of dehydration. The combination of dehydration and high body temperature can cause a number of physiological problems such as: a reduction of blood volume, an increase in the breakdown of liver and muscle glycogen (a sugar used for muscle energy), and the inability of the body to effectively pass certain electrolytes across the cells membranes.

While obviously it is recommended that people who exercise should replace 100% of the fluids lost, it is seldom done. The normal person will replace only about 50% during the exercise period. Dehydration of 4% of the body's weight will reduce one's endurance by 30% in temperate conditions but by as much as 50% when the weather is very warm.

Exercise in cold weather also requires adequate fluid intake. You must warm the air you breathe and your body is still producing heat. You will tend to produce more urine. These factors require you to take in more fluid. If you don't, your body will feel colder because your blood will not have sufficient volume to warm your skin effectively with the heat which it picks up from the exercising muscles.

Dehydration due to excessive heat and/or inadequate fluid intake can cause serious heat related illnesses. A sudden change in the heat or humidity where you practice or traveling to a warmer or more humid climate to compete can cause problems. If you were to travel to India, Egypt or the Caribbean to compete in a marathon, it would probably take 10 days to two weeks to acclimatize yourself to the warmer or more humid climate.

Among the changes which will probably occur in a high heat environment are: a reduced heart rate (due to less need for blood to heat the skin - resulting in less blood flow to the skin), an increase in the amount of blood plasma, increased sweating, perspiring earlier when exercising, increased salt losses, and the psychological adjustments made to the experience of greater heat and humidity.

Adequate fluid is essential to the functioning of an efficient body. When body fluids are reduced by sweating less fluid is available in the blood and other tissues. These make the body less efficient and, in some cases, can result in serious sickness or even death. To keep your body hydrated you should have frequent breaks for fluid intake. However, even frequent breaks seldom give an exerciser enough fluid. A person's thirst does not signal the true need for fluids.

The ingredients of sweat change as you exercise. At the beginning there are a number of salts excreted. Sodium chloride (common table salt) as well as potassium, calcium, chromium, zinc, and magnesium salts can be lost. The initial sweat contains most of these salts but as the exercise continues, the amount of salts in the sweat is reduced because some of the body's hormones come into play. Aldosterone, for example, conserves the sodium for the body. Consequently the longer we exercise the more that our sweat resembles pure water.

A comprehensive study of blood changes during a marathon has indicated that the sodium ions were not significantly reduced and potassium actually increased. This may make us question the need for these minerals in sports drinks. However the sugars and water in the sports drinks may be needed. The average marathon runner loses about 4 pounds during the race. Most of this is water with some of it coming from the use of sugars (glycogen) and body fats. (About 2900 kilocalories are used in a marathon run.) During the run the body creates some water as it uses the glycogen (stored sugar) for energy. About 36 ounces (1300 grams) is produced in this process. Urination is also decreased thereby saving the body's water store. (3)

A normal diet replaces all of the necessary elements lost in sweat. Drinking a single glass of orange or tomato juice replaces all or most of the calcium, potassium and magnesium lost. Further, most of us have plenty of sodium in our daily diets.

Fluid replacement drinks on the market are not necessarily recommended. Water, the most needed element, is slowed in its absorption if the drink contains other elements such as salts and some forms of sugar. Water alone is therefore generally the recommended drink for fluid replacement - and it is certainly the least expensive. For those who want to replace water and sugars for energy the best drinks are those which contain glucose polymers (maltodextrins). So if you are using fluid replacement drinks, check the label then buy what you need - salts and/or sugars. Both caffeine (coffee, tea, and cola drinks) and alcohol dehydrate the body so should be avoided.

There is no question that adding carbohydrates, such as maltodextrins, is highly effective in replacing your body's fuel. In a study of marathon runners given either a high carbohydrate drink or a placebo every 15 minutes during a run, those receiving the high carbohydrate drink were able to keep the blood sugar glycogen much higher during and after the run. (4)

While water is generally recommended as the drink to replace lost perspiration, there are times when some electrolytes (sodium, potassium, etc.) must be replaced. People working in the heat in hard manual labor, marathon runners, soccer players playing under the summer sun in Texas or Arizona, and similar vocational or avocational warm weather pursuits will probably need extra electrolytes. In a study testing whether sodium or sugars (glucose) was more important in the body absorbing water, it was found that the sugars were more important in fluid replacement beverages. (5)

However, one study, with trained runners on a 2 hour treadmill run at 60% of V02 max found that heat was controlled the same whether the runners received either 8% carbohydrate carbonated drinks, 8% non-carbonated drinks or water. (6) This study indicates that you can drink whatever you want - just drink. But it is the water, more than anything else, which is essential.

In the Commonwealth Games in Malaysia in September of 1998 Craig Barrett of New Zealand was leading the 50 kilometer walk by 6 minutes with a kilometer left in the race. He was a sure winner, but the heat of Kuala Lumpur was far greater than that in which he had been training in New Zealand. He had not taken in enough water and electrolytes and heat exhaustion overcame him. He fell, got up, fell again, then staggered to the side of the road and was taken to the hospital. He had not only become incapable of moving his legs but he was delirious and had no idea what was happening. When he regained consciousness in the hospital he thought he had won the race.

A British study using 12 male and 6 female well trained middle distance runners who ran six one hour runs, three indoor and three outdoor. In one indoor and one outdoor run no fluids were given. This gave an indication of the amount of fluid loss during the run. In one indoor and one outdoor run water sufficient to replace the fluid loss registered in the first run was given. In the third indoor and outdoor runs a sport drink was administered. The results showed that per pound of body weight, the men lost twice as much fluid as the women - about 1.9 kilograms for the men to 1 kilogram for the women. Both the water and the sport drink were equally effective in maintaining the blood volume, heart rate, body temperature and blood lactate levels. The sport drink, as should be expected, was superior in maintaining a higher blood glucose level. (7)

If you are exercising for more than 15 minutes or exercising in the heat you must be conscious of your need for fluid. In such situations it may be wise to eat a diet higher than normal in potassium and, depending on the amount of sweat, some extra sodium. You might consume a drink with extra electrolytes, such as V-8 juice or orange juice, or a sport drink with these elements. (8) Even a minimal level of dehydration (less than 2% loss of body weight due to perspiration) impairs the cardiovascular and the heat regulating abilities of the body. Even when exercising for less than an hour fluid replacement is essential. (9)

Problems Caused by Heat

Heat cramps are generally found in the cramping of the legs, arms or abdomen. The victim will be able to think clearly and will have a normal rectal temperature. The treatment is to give fluids with salt and possibly other minerals - as are found in most fluid replacement drinks. Heat cramps are particularly common among exercisers who are not yet in good physical condition and who are participating during warm days. There should be no problem in returning to activity the next day.

Heat exhaustion is generally caused by too little fluid or insufficient salts in the body. Water depletion heat exhaustion is caused by insufficient water intake or excessive sweating. The symptoms may include: intense thirst, weakness, chills, fast breathing, impaired judgment, nausea, a lack of muscular coordination and/or dizziness. If untreated it can develop into heat stroke - a rectal temperature of over 104 degrees F (40 C). The immediate treatment is to give water or an electrolyte replacement drink, When the case is severe it may require intravenous fluid replacement. The skin will generally feel cool and somewhat moist.

Salt depletion heat exhaustion appears to be similar to heat cramps. This can occur when large volumes of sweat are replaced only with water. If a great deal of salt was lost in the perspiration it can affect muscle functioning. It is most likely to occur during the first 5-10 days of exercising in the heat. The symptoms may include: vomiting, nausea, inability to eat, diarrhea, a headache (particularly in the front of the head), weakness, a lower body temperature and muscle cramps. Weight loss and thirst are not symptoms of this problem.

Heat stroke can be caused by heavy exercise just as it can by high air temperature. It is a very serious condition which can affect many of the organs. It can occur when the interior organs of the body are heated above 106 degrees F (42 degrees C). At this temperature protein begins to break down. Enzymes are affected as are the cell walls. When the cells cannot function effectively, the organ functioning is impaired.

In addition to a body temperature in excess of 104 degrees F (40 degrees C) there can be a rapid pulse (100-120 beats per minute) and low blood pressure. There may also be confusion, weakness, fatigue, delirium, or the victim may lapse into a coma. The confusion which may be exhibited is often confused with a head injury in contact sports. The skin color is grayish indicating poor circulation, and it will be clammy. There may or may not be sweating. The pupils of the eyes may be very small.

Treatment requires the immediate cooling of the body. Don't wait for the hospital to treat the victim. It may be too late. Use ice packs to the neck, and groin. Full immersion in a tub of cold water is better. One who has experienced a heat stroke should not return to activity for at least a week or two.

Reducing the Risk of Heat Related Problems

To prevent these heat related problems athletic trainers often require that athletes regain 80% of their fluid loss before leaving the locker room. So if an athlete weighed 150 pounds before the practice and 146 pounds afterward, the trainer could require that the athlete take in enough fluids to bring the weight back to slightly over 149 pounds before leaving the facility.

If you are concerned about overheating during your workouts it is recommended that the temperature be taken with a rectal thermometer. The temperature during and immediately after exercise should be below 104 degrees. If you were to use another type of thermometer it would not give a true "core body" temperature because it would be affected by the cooling effects of sweating and other factors.

The best warm weather clothing is no clothes. But unless you are running in a nudist camp you had better wear something. Changing to dry clothes is not advised because the evaporation effect is maximized when the clothing is wet.

Cold Related Problems

Females exercising, at the same intensity as men in cold weather (24 degrees F or -5 degrees C) maintained about the same amount of heat production. But by the third hour the females' heat production dropped significantly below that of the men. Exercising in coldwater (68 degrees F, 20 degrees C) men increased their metabolic activity while women did not. However the rate of body cooling was greater for males than females. This gives female swimmers an advantage in reducing complications from the coldwater. (10)

Exercising in cold air may dry out the mucous membranes because cold air cannot hold as much water vapor as warmer air. Wearing a mask which traps the exhaled water vapor then can re-humidify the inhaled air can reduce this problem. However most problems relate to the effect of the cold temperature on the skin.

Frostnip occurs when the ends of the fingers, toes, ears or nose are chilled. The skin is very cold and somewhat stiffened. Warm the body part slowly. Using your hands to warm the affected area is best. The armpits may be used to warm chilled fingers.

Frostbite can begin with temperatures as high as 31 degrees (F) (-0.5 C). The most likely victims are people who have had the problem previously (a doubled rate), blacks, and of course those who work or play outdoors in cold temperatures. Frostbite can be superficial or deep and severe.

When frostbite has occurred, gently warm the area. Do not rub it to increase circulation because the rubbing can destroy the cells, which have been frozen. A warm bath (104 to 108 degrees F (40-42 degrees C) is helpful. For severe frostbite the victim should be hospitalized where the re-warming can be done under proper supervision.

Proper protection is essential to avoid the problem and is doubly important to those who have already had one case of frostbite. Layers of wool clothing, vapor barrier clothing, adequate gloves, and a face mask if necessary. Outdoor practices and games are not recommended if the ambient temperature is -4 degrees Fahrenheit (-20 C) or the wind-chill factor is -40 F.

Hypothermia is a generalized body cooling. While the cooling is generally not as dangerous to body tissues as is heat, there is still a danger of death. It can occur quickly, such as when a person falls into very cold water, or slowly, when the person is exposed to low air temperatures.

Dehydration often occurs because the blood flow to the skin is reduced. This increases the volume of blood in the organs. The liver senses the increased blood volume so removes the excess water from the blood. This results in less total water in the body.

The people most susceptible to this type of problem are: older people (because of their reduced metabolic activity), young people with large skin surfaces but less body mass (i.e. tall thin teenagers), hypoglycemic or diabetic people, and those with reduced glycogen stores (energy reserves) due to physical exertion or shivering.

Hypothermia can begin with outside temperatures of less than 64 degrees (F) (18 C) especially if it is wet. Long distance races and other endurance events in these low temperatures can cause problems. Swimmers, free divers, or scuba divers are particularly prone to the possibilities of hypothermia because water conducts heat away from the body 32 times more rapidly than does air.

The symptoms, in addition to feeling cold and shivering, may include: poor judgment, confusion, muscle stiffness and unconsciousness. If hypothermia is diagnosed get the person to the hospital as quickly as possible.

The hospital can use special internal and external warming methods. Cold wet clothes can be removed and the body should be insulated against further cold. The body can be warmed with the victim's own body heat or in a warm room.

Prevention of cold injury is best done by dressing in wool or polypropylene clothing. (Cotton is not recommended because it holds perspiration and increases the heat loss through conduction.) The clothing should be in layers to reduce the body's heat loss and cold absorption through the better insulating qualities of the multiple layers and the trapped air between the layers. Effective gloves or mittens, a warm hat and/or ear muffs, wool socks, and possibly a woolen or other mask.

Air Pollution

The most common sites for air pollution are urban areas, especially near well traveled roads (carbon monoxide, lead, oxides of nitrogen and sulfuric acid), indoor ice rinks (oxides of nitrogen), and swimming pools (chlorine forming cancerogenic chloroform). Among the common air pollutants from autos and oil refineries are: carbon monoxide, sulfuric acid, carbon dioxide, oxides of nitrogen, and lead.

Runners in urban areas generally have high levels of lead in their blood. This is occurring while the levels of blood lead are being reduced in the general population because of the use of lead free gasoline.

Air is a limited resource. Normal air contains 21 per cent oxygen. When the percentage of oxygen in the air drops to 16 per cent, the brain is affected. Life cannot be supported if the oxygen level drops to six per cent. Vegetation takes in the carbon dioxide which we breathe out, then gives off the oxygen that we breathe in. This process is one aspect of the phenomenon called photosynthesis. An acre of beech trees in a forest consumes 2,000 pounds of carbon dioxide while giving out 1500 pounds of oxygen each day.

Motor vehicles burn more than 600 million gallons of gasoline each day in the U.S. This burning increases nearly all the pollutants in the air. In a city such as Los Angeles automobiles and trucks produce 45 tons of aerosols, 585 tons of nitrogen oxide, 35 tons of sulfur dioxide, and 9,775 tons of carbon monoxide daily. Aircraft add an additional 19 tons of nitrogen oxide and 190 tons of carbon monoxide to that city's air.

Sulfur compounds are a problem. Sulfur dioxide plus oxygen in the air becomes sulfur trioxide, which is more irritating than sulfur dioxide. The sulfur trioxide then combines with water vapor in the air to become sulfuric acid. (The chemical formula is 2SO2 + 02 = 2SO3 + 2H20 =2 H2SO4). Coal, which is 1%-5% sulfur, is a major contributor to the sulfur dioxide content of the air. The sulfuric acid is bad enough on our lungs and on painted surfaces but it is then picked up through convection and becomes an ingredient in the acid rain which has become quite common in the northern latitudes. Sulfuric acid is the most destructive to lung tissue.

Carbon monoxide released by burning, especially burning gasoline, is picked up by the hemoglobin in the blood. The hemoglobin is then rendered useless in transporting necessary oxygen to the tissues. The heart must work harder and the blood pressure is increased. This strains the heart by making it work unnecessarily.

Carbon monoxide in the blood is increased while driving a car, standing on a busy road, or just living in the city. In downtown Los Angeles, carbon monoxide has been measured as high as 400 parts per million. At 600 parts per million, drowsiness occurs, and at 1,000 parts per million, a person could go into a coma. Exposure to carbon monoxide of one per cent in the air for five minutes could be fatal.

Among the symptoms of carbon monoxide poisoning (high carbo-oxihemoglobin) levels are: headache, nausea, dizziness, and a lack of muscular coordination. Such poisonings are most likely to occur to people who work near automobiles - mechanics, policemen, and parking-lot attendants.

Ozone is a type of molecule of oxygen which performs a necessary function of filtering out some of the harmful radiation of the sun. This occurs in the upper atmosphere 8-30 miles above the earth's surface. In the last ten years there has been a 5% loss of ozone in the stratosphere due to the use of chlorofluorocarbons CFCs) from spray cans and the Freon used in air conditioning gases. Every drop of 1% in ozone is expected to increase the amount of ultra violet (UV) light which reaches the ground. This increases skin aging and serious skin cancer. It also increases cataracts, the hardening of the lens in the eye.

Closer to the ground ozone is an irritating element of smog. Rats exposed to ozone develop lesions in their bronchial tubes and lungs but do not seem to develop cancer. (11)

Various studies have indicated that some people may be able to build a tolerance to the negative effects of ozone. In general, residents of Los Angeles have developed some capacities for rebuilding lung tissues damaged by the pollutant. On the other hand, people with chronic emphysema, respiratory diseases, or people who have not been exposed to smog (such as many residents of Canada) do not have such abilities.

Lead in gasoline is another air pollution problem. Approximately three million tons of lead have been released into the atmosphere since it was added to gasoline in 1923. Poisoning begins when the level of lead in the body reaches 0.8 parts per million. Recent samples have shown that the average person in the U.S. has between 0.05 and 0.4 parts per million in the blood. The blood concentration is generally higher in areas near large numbers of automobiles. So far, no known deaths have occurred due to airborne lead poisoning.

The possible effects of air pollution are many. Lung cancer and emphysema are the most common that come to mind; but increased carbon monoxide levels could certainly increase heart attack rates by increasing blood pressure and making the cardiovascular system less effective. People living in urban areas have twice the lung cancer rate as those who live in rural areas.

Sulfuric acid has been found to be a constrictor of the bronchial tubes leading to the lungs. This is a particular problem for those with asthma but also affects many other people. With the bronchial tubes reduced in diameter it is more difficult to inhale and the necessary oxygen is decreased - thereby cutting ones endurance.

The oxides of nitrogen also reduce the ability of the respiratory organs (bronchial tubes and lungs) to function effectively. They also increase the risk of infection. Nitrogen is increased where propane (liquid nitrogen) is used as a fuel, such as in indoor ice rinks where the machines which clear and smooth the ice are generally propane powered.

Meteorological reports will generally give one the air pollution level for the next day. When it is high your workouts should be reduced or eliminated. Training is safer if it is done away from heavy traffic patterns and before or after rush hour.

Notes

1. J. Pivarnik et al., “Menstrual Cycle Phase Affects Temperature Regulation During Endurance Exercise,” Journal Applied Physiology 72 (1992): 543-548.
2. E. Haymes, “Environmental Challenges,” Women in Sport, ed. B. Drinkwater (Oxford: Blackwell Science, 2000): 65
3. J. Pastene et al., “Water Balance During and After Marathon Running,” European Journal of Applied Physiology, 73 (1996): 49-55.
4. D.C. Nieman et al., “Carbohydrate Supplementation Affects Blood Granulocyte and Monocyte Trafficking by not Function After 2.5 Hours of Running,” American Journal of Clinical Nutrition 66.1 (1997): 153-159
5. C.V. Gisolfi et al., “Effect of Sodium Concentration in a Carbohydrate-Electrolyte Solution on Intestinal Absorption,” Medicine and Science in Sport and Exercise 27.10 (1995): 1414-1420.
6. M.S. Hickey, D.L. Costill and S.W. Trappe, “Drinking Behavior and Exercise Thermal Stress: The Role of Drink Carbonation,” International Journal of Sport Nutrition 4.1 (1994):8-21.
7. J.A. White et al., “Fluid Replacement Needs of Well-Trained Male and Female Athletes During Indoor and Outdoor Steady State Running,” Journal Sci Med Sport 1.3 (1998):131-142.
8. M.J. Leutykemeier et al., “Dietary Sodium and Plasma Volume Levels with Exercise,” Sports Medicine (New Zealand) 23.5 (1997): 279-286.
9. R. Murray, “Dehydration, Hypothermia, and Athletes: Science and Practice,” Journal of Athletic Training (Dallas, TX) 31.3 (1996): 248-252.
10. E.M. Haymes, “Environmental Challenges,” Women in Sport, ed. B. Drinkwater (Oxford: Blackwell Science, 2000): 67-68.
11. G.A. Boorman et al. “Toxicology and Carcinogenesis Studies of Ozone,” Toxicology and Pathology 22:5 (1994): 545-554.

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