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Tuesday, April 08, 2008

London Marathon 2008 Weather forecast

Ambient temperatures might be optimal

Well in spite of cool temperatures in most climes, it is going to be a hot week here at The Science of Sport. The swimsuit debate continues to heat up, the Olympic torch relay is being protested with a vengeance in every city so far, and let's not forget that the 2008 Flora London Marathon is this Sunday, 13 April. As we mentioned at the end of last week, organizer Dave Bedford as once again assembled a legendary field. We will analyze both the men's and women's fields later in the week, though, and today we will focus on the weather.

Most of us who run or are running fans have, at one time or another, heard that records are set in cloudy and cool conditions. This anecdotal evidence is then supported by our own experiences of running in similar conditions. How many of us get that feeling on crisp autumn days that we can run forever? Conversely, how many of us get the feeling in the middle of summer that all we can manage that day is a measly five km because the heat seems to oppressive?

To many it would seem, then, that there is an optimal range of environmental conditions that will be conducive to great performances, be them world records or personal bests for weekend warriors. The forecast for London on Sunday is for partly cloudy skies with a temperature around 10 C and humidity around 80%. What will this mean for the performances?

Science answers

Fortunately for us a group of scientists from the U.S. Army's Research Institute for Environmental Medicine took the time to analyze this concept. The result was two papers (here and here) published last year in Medicine and Science in Sports and Exercise. The primary thrust of the research was to investigate how the weather impacts race time, and if this idea that fast (and record) times are produced only in cloudy and cool conditions.

In the first paper, "Impact of weather on Marathon-running Performance," the scientists examined seven North American marathons. They divided them into different temperature categories and then they analyzed the top three finishing times to see how far off they were from the course record. They also examined the 25th, 50th, 100th, and 300th finishing times and compared them to the course record. Effectively they wanted to see just how much the weather was slowing down the runners, both fast and slower (middle-of-the-pack) alike.

Not surprisingly, the times were closer to the course records when the temperatures were milder. Specifically, when the ambient temperature was between 5-13 C and the humidity was 17-100% the top three times in the race were within 1.7% of the course record. Given London's course record of 2:05:38, 1.7% translates into about a two minute decrement, or around 2:07, which is where the winning time has been since Khannouchi set the world record there in 2002.

Clouds or no clouds, they run fast

The second paper, "Neither cloud cover nor low solar loads are associated with fast marathon performance," took a more detailed look at the specific weather conditions and tried to determine if record times are really run in those "I-could-have-run-forever" conditions. The results of this one might surprise you!

From the figure below (click to see a larger image), we see a frequency distribution on the y-axis and the ambient temperature in Celsius on the x-axis. Each column is divided into sections the represent (from bottom to top) cloudy, partly cloudy, scattered clouds, and clear conditions. The graph on the left represents all of their data, while the graph on the right represents just the course records.

The first thing you notice should be that their is a normal distribution across the range of temperatures, and nearly 80% of the course records were run in the milder conditions of 5-15 C. However you must also see that the course records were run in a wide range of conditions, with cloudy and clear and everything in between represented in apparently equal proportions. The conclusion here is that we are likely to see a fast time regardless of the cloud cover, and that the ambient temperature is a better predictor of the winning time.

Looking ahead to Sunday's race

As we stated above, the forecast for race day is partly cloudy skies, around 10 C, and about 80% humidity. These fall right in the middle of the "optimal" conditions for a fast time, and not coincidentally are common conditions for London in April. Therefore it is no wonder that the average winning time for the last 10 years is 2:07:08 and that Khannouchi set the world record there back in 2002! Interestingly, however, Sunday might be a few degrees warmer than the average temperatures of 7.8 C (men) and 14.3 C (women) during previous world record performances.

Later this week we will have a full preview of both the men's and women's races, so please come back and join us for those!


ELY M, CHEUVRONT S, and MONTAIN S. Neither Cloud Cover nor Low Solar Loads Are Associated with Fast Marathon Performance. Medicine and Science in Sports and Exercise. Vol 39, Issue 11. November 2007.

ELY M, CHEUVRONT S, ROBERTS W, and MONTAIN S. Impact of Weather on Marathon- Running Performance. Medicine and Science in Sports and Exercise. Vol 39, Issue 3. March 2007.


Andrew said...

Absolutely fascinating! I love these types of articles. Some observations:

1) Optimal conditions for women seemed to be slightly warmer than for men. Is there a physiological reason for this?

2) Cloud cover seems to be a factor in the 0-10 degree races as a trend toward favoring sunnier conditions. Since solar radiation DOES provide warmth, maybe it helped drive the effective conditions for the body closer to the optimum 10-13 degree range cited by the first paper.

3) Conversely, I can see why cloud cover wouldn't help warmer races. In warm weather, sunshine and dry air usually go together as does clouds with humid weather.

The Sports Scientists said...

Hi Andrew, and thanks for the comment!

Yes, I also noticed that the temps when women set their records were slightly higher than when men set theirs.

Recent research has kind of nullified the perceived differences between men and women when it comes to thermoregulation, so it is not entirely clear why the women set their records in warmer temps. It could just be entirely coincidental and more a function of the fields at the cooler races.

Great observations about the cloud cover. Indeed, when the temps dip then suddenly cloudy conditions mean it will be colder. And even though the guys are running at very high metabolic rates, when the ambient temp is 0-5 C and there is no sunshine even they tend to get cold and uncomfortable and suffer from the conditions.

Thanks again for visiting!

Kind Regards,

Unknown said...

Just a nit, but I always find myself doing lots of conversions when I read your articles. Those of us in the US have no idea what 5 degrees Celsius feels like so we have to go to Google and convert. Same thing for race paces expressed in min/km instead of min/mile.

Please support us backwards Americans to make your articles more readable. A simple 5-13C (41-55F) would go a long way.

Thanks for the great blog and keep up the good work,


Hung-Kwong Ng said...

I am little confused on this.

The first study says: "there is a progressive slowing of marathon performance as the WBGT increases from 5 to 25 degrees C".

The 2nd study says: "Neither cloud cover nor low solar loads are associated with fast marathon performance."

Is it saying when race temps are high, cloudy cover does not affect marathon performance?

I bought a WBGT thermometer and collected some data during my 170 mile ultramaraton last weekend. The WBGT read 77F in full sun and dropped to 72F when a cloud drifted pass. I regret not collecting data when I approached the finish line in 90 degree heat at 5pm in full sun. I think cloud cover would have improved my time.

It would be interesting to study Ironman Triathlons that last into the afternoon.