Increased carbon monoxide and ozone levels slow you down, tire you out, and are bad for your health. Avoid pollution as much as you can, but do not skip your workout.
Air pollution is a mixture of thousands of chemicals, some of which are gasses such as carbon monoxide and nitrogen oxide, and others are particulate matter (very small particles). The interactions of pollutants with one another or with the environment create further harmful chemicals, such as ozone, which is formed from nitrogen oxides and volatile organic compounds in the presence of sunlight.
Scientists believe that most pollutants cause the formation of free radicals in your airways, which leads to an anti-inflammatory reaction and a low level inflammation. This is not only bad for your respiratory system, but also for the rest of your body.
When you are working out, you are inhaling more pollutants because you are breathing harder. Moreover, as you are breathing through your mouth, the air does not get filtered by your nose. The increased airflow will also bring the pollutants deeper into your lungs, and as your body tries to take up more oxygen, you will probably be taking up more pollutants too.
Carbon monoxide binds better to haemoglobin (= the substance that carries oxygen in your red blood cells) than oxygen, which means that less oxygen will be delivered to your muscles. Your heart will have to work harder, your VO2max (a measure of your maximal work rate) will drop and lactate will accumulate earlier than normal. Fortunately, the binding of carbon monoxide with haemoglobin is reversible, but it will take about three to four hours to free half of your haemoglobin.
It is therefore a bad idea to sit in traffic before a race, or even to go to a smoky pub the night before.
Ozone and particulate matter
Ozone acts on the muscles of your airways and makes deep breathing difficult. High levels will make you cough and hyperventilate, and you will not be able to run as hard as usually. It also reduces the diameter of your blood vessels, influences your heart rate, and might even increase your blood pressure. It is therefore linked with cardiovascular disease and death.
The effects are worse when it is hot, and can vary from one person to another. The good news is that in the UK levels are usually low, but the bad news is that it can travel considerable distances. You are therefore not safer in rural areas than in an urban environment.
Particulate matter is not known to affect your athletic performances, but it is associated with a higher risk of cardiovascular disease.
To run or not to run?
As yet, most studies have just looked at what happens when you are exposed to air pollution during exercise, and it is obvious that it is far better to exercise somewhere where the air is clean. However, as most of us live in cities, we need to know if the benefits of exercise are larger than the disadvantages of inhaling pollutants.
Scientists are not absolutely sure yet, but there are some powerful hints that exercising is still the better option.
Several studies have indeed shown that commuting to work by cycling is much better for your health than going by car, even through cities. Moreover, a study comparing mice after five weeks of exercising in polluted air with mice that were sedentary in the same conditions showed that lung inflammation and oxidative damage were much more important in the latter.
However, mice might react differently than humans, and running is a more strenuous exercise than cycling to commute. We need more studies.
- Avoid busy roads: pollution drops fast as you are moving away from traffic.
- Run through parks: new data have shown that vegetation can reduce pollution by up to 40 to 60 %, which is much more than we previously thought.
- Run early or much later in the day: ozone levels rise steadily throughout the day and are highest when the sun and temperature are at their peak.
- Eat plenty of fruit and vegetables: make sure your anti-oxidant defence system is in the best possible condition.
Disclaimer: this article is for general information only, and does not replace medical advice. It cannot be used to diagnose or guide treatment. If you have any concerns or questions, you should talk to a qualified health provider.
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