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December 19th, 2005:

Dont run in smog

Dont run in smog

Monday, December 19, 2005

Letter to the South China Morning Post

We believe that many of your readers are interested in whether physical exercise in an environment of polluted air is harmful to health. We would like to follow up on the letter “Running in smog risky” (December 12), by Wong Chit-ming, Lam Tai-hing and Anthony J. Hedley, who suggested that there were no studies addressing this important issue.

Some years ago, we conducted an epidemiological study of the association between air pollution and cardiopulmonary fitness of primary-school children in Hong Kong. We showed that physical exercise was positively associated with cardiopulmonary fitness in those children who lived in and attended schools in the less-polluted district in our study, but not in children living and attending schools in the more-polluted district.

In other words, the beneficial effect of physical exercise that we all know seems to have disappeared among children exposed to an environment with high air pollution, in contrast to those living in a district of relatively clean air.

In our study, cardiopulmonary fitness was represented by “maximal oxygen uptake” – the maximum amount that a child can consume during maximum physical effort. The higher the oxygen uptake, the fitter the child. We estimated this parameter by an indirect method, using a standard test widely adopted in sports science. The study is called “Impact of air pollution on cardiopulmonary fitness in schoolchildren.”

Owing to limitations in the study design, our results could not demonstrate a definite cause-effect relationship, but the conventional wisdom that physical exercise is always beneficial to health must be questioned. Specifically, we consider it prudent to refrain from strenuous physical activity in highly polluted environments, for example, jogging on roads with moderate to heavy traffic. Moreover, the potential harm to the health of children playing in school grounds that are exposed to heavy traffic fumes should be urgently assessed.

WONG TZE-WAI and IGNATUS YU TAK-SUN, department of community and family medicine, Chinese University of Hong Kong