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How does air pollution affect marathon times?

February 21st, 2010

There are a couple of different ways you could pitch a new study on air pollution and marathon performance from the March issue of Medicine & Science and Sports & Exercise. The good news is that levels of six key pollutants almost never exceed EPA guidelines during seven major U.S. marathons (Boston, Chicago, New York, Twin Cities, Grandma’s, California International and Los Angeles). And when you compare top times to pollution levels, there’s no correlation in all but one case.

Or you could do it the other way around: Danger! Elevated levels of particulate matter smaller than 10 micrometers (PM10) make women run more slowly, even when levels are well below EPA guidelines!

The study is by Linsey Marr of Virginia Tech and Matthew Ely of the US Army Research Institute of Environmental Medicine. It looks back at marathon results from the past 28 years (or as long as available) and digs up accurate pollution readings for the races. To assess performance levels, they look at the top three men and women’s times as a percentage of the existing course record. They also use the results of a previous study to subtract out the variation due to temperature, humidity and solar radiation.

The main finding is that major marathons have pretty good air quality, even in big cities. They’re held on weekend mornings, so they avoid the rush-hour car pollution, and they’re generally early enough in the morning that they avoid the secondary pollutants like ozone which are produced by intense solar radiation.

Despite that fact, it wouldn’t have been a big shock to find that higher pollutant levels — even below the usual thresholds — were associated with slower times. After all, as the authors note:

An athlete running at 70% of maximal oxygen uptake for the length of a marathon (~3 h) inhales the same volume of air as a sedentary person would in 2 d. In addition to the elevated ventilation rate, the switch from nasal to mouth breathing and an increased airflow velocity carry pollutants deeper into the lungs and further amplify the runner’s dose of pollutants.

In the end, though, the only correlation that showed up was between PM10 and women’s (but not men’s) times. This isn’t the first study to find that women may be more sensitive to certain pollutants than men. The theory is that their narrower larynx openings lead to greater turbulence in their airways, which results in greater deposition of pollutant particles.

For what it’s worth, the Beijing Olympics — whose high pollution levels stimulated this study in the first place — had PM10 levels well above the highest levels included in this study. Could this have been a factor in the result?

It is interesting to note that despite relatively high PM10 concentrations of 87 [micrograms/m3] on race day, the men’s marathon winner set a new Olympic record. In addition, the average of the top three men’s finishing times was faster than the preexisting record. During the women’s marathon, PM10 concentrations averaged 62 [micrograms/m3], and the top three women were 2.6% slower than the Olympics marathon record.

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