09/28/2007 08:00 am ET Updated Nov 17, 2011

Exercising Outdoors in Major Cities May Not Be A Walk in the Park

You don't exercise to get sicker. But that's the price many pay to use the outdoors in America's big cities as a venue for brisk sports. Blame air pollution for the bad news.

Air pollution affects members of the population who have underlying respiratory problems such as asthma, bronchitis, and emphysema. However, people who do not have respiratory problems may be at risk, people who power walk, jog, rollerblade or cycle in the city environment which contains many environmental irritants that affect the lung and respiratory system.

We often think of these exercise enthusiasts as being afflicted with musculoskeletal and orthopedic problems such as foot, knee, and back pain, yet there is serious concern for the development of these more serious cardiopulmonary maladies.

How many times have we seen people rollerblading, cycling, or jogging on a busy street behind a bus which is emitting all of this black exhaust and smoke? How beneficial is this otherwise healthy physical activity in this dangerous setting? Does exercise in the presence of these potentially dangerous conditions make it unhealthy?

"Outdoor air pollution is the result of automobile and industrial emissions. The major culprits are ozone, fine particulate matter, and carbon monoxide. Epidemiologic studies have linked these pollutants to increased exacerbations of heart and lung disease, emergency hospital admissions, and deaths", says Dr. Joseph Cooke, a pulmonary specialist and Associate Professor of Clinical Medicine and Public Health at New York Presbyterian- Weill Cornell Medical College.

Ozone concentrations are of major health concern during the summer months. This compound is a large component of the smog found in Los Angeles. Sunlight interacts with chemicals found in car exhaust known as hydrocarbons and produce ozone. Carbon monoxide needs no introduction. It is everywhere and is known to arise from cigarette smoke and car exhaust. What makes carbon monoxide so dangerous is its tremendous ability to squeeze oxygen out of our circulatory system. It combines with hemoglobin 200 times faster than oxygen. It is often fatal and overexposure may lead to headache, dizziness, confusion and dangerous increases in body temperature.

Dr. Cooke observes that pollutants affect the lungs by causing inflammation or irritation of the airway lining. This, in turn, increases the production of mucus and phlegm, and small muscles surrounding the airway respond by squeezing down. The airway becomes smaller, and it becomes more difficult to move air in and out of your lungs. Your body works harder to breathe, and it becomes more difficult to get oxygen into your body. As a result, exercise becomes stressful and performance suffers.

The normal response to exercise is to breathe deeper and faster. This will increase your exposure to pollutants and their effects. Dr. Cooke warns that "common symptoms of this pollution exposure include chest tightness, cough, shortness of breath and wheezing." So what's the fix?

Dr. Cooke recommends that if a person has heart or lung disease it is best to exercise indoors, in an air-conditioned environment if possible. If you must go outdoors, the early morning or evening is best. It will be cooler, the sun is not at its peak, and the ozone levels will be at their lowest."

Here are some helpful hints to keep exercise healthy in the city:

Avoid roads which carry heavy truck traffic. "Work out" when there is less vehicular traffic, such as during very early morning or later in the evening.

Exercise indoors if at all possible.

Most importantly, if you experience any difficulty breathing, stop your exercise activity immediately and see a lung specialist.

Even the experts assert that exercise is keenly needed, but also maintain that exercise must be modified in the city to reflect true world conditions. You can have the best of both worlds, accordingly.