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SHOULD YOU RUN IN A PURPLE HAZE?

Runners experience life to its fullest. We feel the heat of the sun and the bite of the wind more intimately than those who shake their heads at us from their car windows. Our hearts, lungs, and muscles strain and improve with our efforts. As we suck up the marrow of life, however, we bring thousands of liters of air into our lungs-air that may be dangerously fouled by pollutants. In fact, urban runners are exposed to much greater quantities of air pollution than sedentary folks due to the large volumes of air we breathe while running.

Particularly in summer, the prudent runner living in or near a city will check local air quality conditions daily. Pollution episodes are often caused by a temperature inversion in which warm polluted air becomes trapped between 2 layers of cooler air. The inversion layer prevents pollutants from dispersing in the upper atmosphere. Summer is also a time for discretion because exercising in the heat increases the detrimental effects of air pollution. Although the mechanism is poorly understood, heat and pollution together cause greater reductions in lung function and running performance than does pollution alone.

The most common types of air pollutants that affect distance running performance are ozone, carbon monoxide, and sulfur dioxide. The body's response to pollution is related to the concentration of the pollutant, and how much air is inhaled. There is a large degree of individual variability in responsiveness to pollution, and asthmatic runners should seek professional medical advice. Let's take a look at the 3 most common villains in our air.

Ozone (O3) is formed when sunlight reacts with automobile emissions. Scientific evidence indicates that running in ozone concentrations > 0.16 ppm can cause impaired lung function and running performance. Running in moderate ozone concentrations can cause coughing, chest tightness, and shortness of breath.

Carbon Monoxide (CO) is formed from burning oil, gas, coal, and wood, and is the most common air pollutant in our cities. Because its primary source is automobile emissions, carbon monoxide exposure is particularly high near urban highways. Carbon monoxide attaches to hemoglobin in your red blood cells which reduces the amount of oxygen transported to your muscles. Scientific evidence indicates that running in carbon monoxide concentrations > 25 parts per million can reduce your VO2 max and impair your running performance.

Sulfur Dioxide (SO2) is produced by power plants, smelters, refineries, and other industries. Running in sulfur dioxide concentrations > 0.5 ppm is likely to cause bronchoconstriction, wheezing, and chest tightness in asthmatics. Although sulfur dioxide concentrations typically found in U.S. cities do not generally cause symptoms in non-asthmatic runners, symptoms may occur during high intensity workouts or races.

Little is known about the chronic effects of exercise in a polluted environment. Lawrence Folinsbee, Ph.D., who has studied exercise and air pollution for over 15 years, acknowledges that more research is needed to determine the relationship between lung function and habitual exposure to air pollution in athletes. Dr. Folinsbee cautions, however, that runners who regularly train in polluted air may experience long-term changes in lung function.

The best strategy for dealing with pollution is to avoid it. A Minnesotan wouldn't go for a run in the winter without checking the temperature, and a Floridian wouldn't run at noon in the summer. Similarly, urban runners should make a habit of considering the environmental conditions. Read the paper, listen to the radio, or scan the internet to check the air quality where you live.

How to minimize your exposure to air pollution:

1. Run in the morning when pollution levels and heat are at their lowest.
2. Avoid running next to busy highways, particularly during the evening rush hour.
3. Cut back the intensity of your workouts. Running slowly allows you to breathe through your nose which removes sulfur dioxide and some other pollutants from the air.
4. If you must race on a polluted day, cut back your warmup to minimize your pre-race exposure.
5. Workout indoors when outdoor air pollution is dangerously high.
6. If an indoor workout isn't an option, take a day off on high pollution days.
7. Take the antioxidant vitamins E and C. There is preliminary evidence that antioxidants help to reduce the harmful effects of air pollution.

Running is the best way to improve your physical and mental well-being. If you live in an environment that experiences potentially dangerous levels of pollution, however, do your health a favor by minimizing your exposure during high pollution episodes. With some planning and common sense, you can safely enjoy running wherever you live.

Exercise physiologist Pete Pfitzinger competed in the Olympic smog of Los Angeles and Seoul.

(This column originally appeared in Running Times Magazine.)