By Daniel G. Graetzer, Ph.D.
Faculty Member, School of Health Sciences
Air pollution and exercise can intertwine in a decidedly negative way. Numerous environmental factors – such as heat, cold, altitude, relative humidity and wind chill – influence the human body during outdoor exercise. In addition, technological advances of the 20th century have introduced several unnatural environmental stressors to people exercising outdoors; these stressors include air pollutants, ozone, temperature inversions and carbon monoxide.
Poor air quality can adversely affect the performance of both recreational and high-caliber athletes during both short- and long-term exercise. Regular aerobic exercise can certainly improve health and cardiovascular fitness. However, running or biking near a busy freeway in a smog-filled atmosphere may make outdoor exercise more harmful than beneficial which means air pollution and exercise comes with its own set of risks.
Airborne pollutants have a much greater influence on the body during physical exertion than during rest. As a result, athletes are often affected by poor air quality while spectators may not notice it.
Physical exercise increases the hazards of contaminated air because the increased rate and depth of breathing exposes more airborne particles to the delicate tissues of the lungs. High-intensity exercise requires a transition from breathing through the nose to breathing through the mouth, which causes the body’s natural air purifying system in the nasal hairs and mucous membranes (very effective at removing pollutants during rest) to be bypassed.
Air Pollution and Exercise Produce Airborne Particulate Matter That Is Difficult to Exhale
The air we breathe has airborne particulate matter (PM) consisting of “small droplets of liquid, dry solid fragments, and solid cores with liquid coatings,” according to the California Air Resources Board. However, the California Air Resources Board also notes that PM-10 and PM-2.5 levels indicate the amount of small industrial-generated particulates (less than 10 or 2.5 microns in size) in ambient air.
These tiny pollutants are more dangerous to inhale than larger particles because they are not trapped in the upper respiratory tract. In addition, they attach themselves to the alveoli (a critical gas exchange area in the lungs) and are too small to be effectively exhaled.
Inhaling Ozone from Air Pollution and Exercise Can Cause Immediate and Long-Term Health Problems
Of all pollutants, ozone is considered the most toxic and presents the greatest danger during exercise. Although ozone gas has only minimal effects during rest, it substantially restricts prolonged submaximal exercise (such as distance running and bicycling) and intermittent short-term maximal efforts (such as football and track/field events).
A high ventilation rate in a high-ozone environment can cause lung irritation, coughing, chest pain, shallow breathing (bronchospasm), headache, and nausea. In addition, long periods of breathing ozone combined with hydrocarbons, aerosols, sulfur, and nitrogen dioxide may be a contributing factor to allergies, asthma, pulmonary emphysema, bronchitis, and even lung cancer.
Temperature Inversions with Air Pollution and Exercise
Temperature inversions are often seen in cities located at high altitudes (with a low partial pressure of oxygen) and in basins surrounded by mountains (which block winds and trap pollutants). A “greenhouse effect” inversion causes a reversal of an ecosystem’s normal atmospheric temperature; harmful chemicals in the air are “cooked” and their effects on the human body is enhanced.
Carbon monoxide, coming mainly from automobile tailpipes, combines quickly with hemoglobin (the oxygen carrying compound in the blood). By taking up binding sites on the hemoglobin molecule, carbon monoxide impairs oxygen delivery to the body’s tissues.
Elderly individuals with heart disease are at special risk to any restrictions in oxygen delivery. This interference with getting oxygen to the body can induce angina (chest pain) or even a heart attack.
4 Ways to Exercise More Safely Outdoors
There are several ways to avoid the unhealthy and restricting effects of air pollution and exercise:
1. Run or cycle on lightly traveled streets or country roads. If you must go briefly along heavy traffic, stay as far from the road as possible to avoid inhaling carbon monoxide from passing vehicles.
Carbon monoxide levels next to urban traffic can average 37 parts per million ppm), rise to 54 ppm in heavy traffic and can peak at up to 120 ppm at stop signals. These high levels may extend about 65 feet from the road. As a rule, running in a windy environment is better than running in stagnant air.
2. Exercise during the early morning or evening hours. Ozone forms 90 minutes after dawn, peaks during midday and drops quickly after sunset. Carbon monoxide levels peak twice during the day, corresponding to morning and evening rush hour traffic.
3. Keep a record of pollutant levels in your area and recommend that sponsors of athletic events avoid heavy ozone and inversion seasons for endurance competitions such as marathons. Ozone levels are highest during the summer (June, July and August) while the inversion season generally lasts from November to February.
During the 1984 Olympic men’s marathon in Los Angeles, California, Olympic organizers made the mistake of scheduling the event to start at 5:15 p.m. on August 15. The evening start time indicated that organizers were more interested in T.V. commercial revenues than the safety of the participants. As a result, the athletes were exposed to very unhealthy air and their athletic performance was negatively affected.
Since this mistake, many sporting contests are now being postponed or canceled in Los Angeles during heavy air pollution episodes. Ideally, such events should be scheduled on weekends, which have less rush hour traffic and higher air quality. Unnecessary traffic along a racecourse should be banned when possible.
4. Get in a clear-air environment as soon as possible after exercise. Carbon monoxide levels remain high in the blood up to four hours after exercise if you continue to breath polluted air, so going to a cleaner environment is helpful. Carbon monoxide levels can also be reduced in locker rooms and indoor arenas by banning smoking inside buildings.
The combination of environmental air pollutants, ozone, temperature inversions and carbon monoxide expose athletes to several unnatural stressors, and inhaling several different pollutants amplifies their harmful effects. While it’s not possible to completely avoid naturally occurring environmental stressors, outdoor air pollution is a threat that should be avoided whenever possible.