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Saturday, October 09, 2010

Chicago Marathon 2010: Heat and performance

Exercise in the heat and Chicago 2010 Preview

Just one day to go now before 10-10-10, as we continue our build up to Sunday.  Earlier this week we took a look at some recent close finishes in the marathon world, two of which occurred here in Chicago.  Today we are going to take a look back to the 2007 race, when unseasonably warm and humid conditions wreaked havoc on the race and forced a premature closure.  The events surrounding that day sparked much discussion and debate here on the site, and sparked our first series, a five-part series on exercise and dehydration.

The most recent forecast for the 2010 race is looking excellent with warmer temps than normal, but minus the suffocating humidity from 2007.  The cooler morning temps might even be mild enough to facilitate a world record---providing Wanjiru can get his pacing right, but that's another post entirely.  For now we will take another look at the effects of heat on performance, and how elegantly we are able to balance our heat production with our losses so as to prevent disaster.

Given:  Heat affects performance

Few would argue this point, because inherently we all know that when it gets hot outside, we slow down.  Of course this occurs without even thinking about it, which is the remarkable part of our physiology.  So on race day 2007 none of those athletes had to first become too hot before slowing down, and instead were already running slower even from the gun.  And the effects of heat on performance are well know and documented so that we can expect a 3-5% decrease in performance compared to cool or neutral conditions.  And in fact that was bourne out in the 2007 race, as the winning time was "only" 2:11:11 compared to most other years when the winning time is between 2:05-2:07.

You might be thinking that is an awfully small difference, but remember we are dealing with the differences in performance in the most highly trained athletes, who have the best ability to cope with the heat not only because of their training status, but also because this group benefits from a smaller body mass.  In fact if you go farther down the field and analyze the every day runners, which we have, you find that the lesser trained and what are most likely "normal sized" athletes are affected in a more dramatic way.

In this first graph, we have compared the 1st, 100th, 1000th, 10000th, 20000th, 99th percentile, and the mean finishing times from 2005, 2007, and 2009.  (Click to enlarge it.)

At a glance you see that the yellow bars, 2007, are generally taller than the other two years---so that is the effect of the heat on performance.  Also, you can see that for the faster finishers the difference is smaller, which tells us they are less affected by the heat.  Interestingly, the 1000th finisher in 2009 was almost 30 min slower compared to 2007, and likewise for the 99th percentile time---it was actually faster in 2007 compared to the two other years.

Admittedly, the absolute differences might not be the most meaningful a way to evaluate the data, which is why we have looked at the relative differences between 2005 and 2007, and between 2007 and 2009.  Again, click to enlarge the graph:

The black bars are the percent different for each finishing place between '05 and '07, which the maroon bars represent the percentage difference between the '07 and '09 races.  Therefore the winning time in 2007 compared to 2005 was about 3% slower, and compared to 2009 the winning time in 2007 was about 4% slower.  This graph shows how as we go down the placings, the slower runners are affected more by the hotter temps, although perhaps at a point---probably where the people are basically walking the entire course, this effect is absent as noted by the 99th percentile finisher.  But on average the times were 8-9% slower in 2007 compared to the '05 and '09.

Don't remind us:  We know the limitations

Before the science stick comes out and we get pummeled with it, we know this is not a definitive analysis of the effects of heat on performance.  We simply grabbed the "X" placed finishing time from each of the three years and looked at how they compare.  Admittedly, looking at percentiles might be slightly better, so we encourage you to crunch the numbers with us---all of the data above are available on the Chicago Marathon website.

Regardless, we still think this paints an interesting picture of how the heat affects performance across a range of running abilities.  Most interesting but maybe not surprising is the finding that the 99th percentile times are effectively the same independent of the environmental conditions.  The reason it is not so surprising is that at that pace---between 6:00-6:30---the "runners" are effectively walking the entire distance or a very large proportion of it, and in doing so they are mitigating the effects of the heat on performance.

Quick preview of the race:  Whip out the SoS crystal ball!

It would have been great for American running, and also for Ryan Hall, if Ryan Hall could have raced against Kebede and Wanjiru.  I think at some point the pace would be too much and he would get dropped, but like Sammy Korir in Berlin 2003 he might have been pushed to a new PR and possibly a new American record.  But given Wanjiru's and Kebede's last few performances, they are the hot favorites.  Wanjiru was unbeatable between 2007 and this year, winning the Olympic gold, London and Chicago last year.  2010 has seen a drop in that form - a DNF in London his worst major marathon performance.  That race was won by Kebede, who has, in his last two marathons, established himself as the eminent marathon runner of 2010.

The race is likely to go one of two ways.  The pace could be suicidal from the gun, as in London 2009 (recall the 1:01 half split! or Chicago 2009 (29:11 for 10 km, 44 min for 15 km).  If that is the case by halfway or shortly after, expect a small pack of 4-5 runners to have formed - this is arguably the strongest ever Chicago Marathon field, and has five runners all with sub 2:06 credentials in it.  The race between these five should last at least to 32km.   What happens from there is maybe anyone's guess - if Wanjiru has regained his 2008-2009 form, then expect him and Kebede to be last men standing.  

The race is full of potential champions though - Robert Cheruiyot produced a sub-2:06 performance in Boston this year, an astonishing performance that many felt is worth a 2:04 (at least) on a Chicago-like course.  So even at world record pace, he'll be in contention.  So too Deriba Merga, the aggressive Ethiopian, will have a say in the race - he may not win it, but he'll dictate how it unfolds with his racing style.  Then there are Vincent Kipruto (3rd in Rotterdam this year) and Feyisa Lelisa (4th in Rotterdam), both sub 2:06 runners. 

The conditions are going to be near optimal for the record to fall, and with five sub-2:06 performers, including Wanjiru and Kebede in the race, it may well be on.  If the wind cooperates (and it might, as the forecast is for SW winds as the day progresses, giving them a potential tailwind down the home stretch) then it all depends on how the race unfolds.  The other option for the race is that it might be fast in the beginning, but the presence of so many potential champions may see the race become more tactical.  In that case, watch for Merga or  Cheruiyot to steal the show much as Marilson Gomes dos Santos did in New York in 2009 while Tergat and the other contenders were busy marking each other.

A friend of mine saw Merga in the hotel lift on Thursday, and he asked him what he would run on race day.  "2:04," he replied.  Whether or not Merga has that kind of speed is debatable, but this is not---he will attack and attack again and stay with the pace for as long as he can.  His 1:02:31 at 2500 m in Colombia is telling, but probably not quite worth a 58:xx time at sea level and therefore probably not good enough for a 2:04:xx marathon.  Our guess is that even if the pace is high, which Wanjiru is known to do, Merga will be able to stay with and even attack up to 30+ km, but will fade after that, perhaps hanging on for a 3rd or 4th place finish behind Kebede and Wanjiru.

On the women's side, it should be a four-woman race between defending champ Liliya Shobukhova, 2008 champ Lidiya Grigoryeva, World Marathon Majors champion Irina Mitikenko and Ethiopian Askale Tafa Magarsa---who ran 2:21 in Berlin 2008.  On paper all of them match up more or less equally, so it could be a really amazing race between those four, but we are unlikely to see any of them come close to Paula Redcliffe's 2:17:187 course record from 2002.

Race day coverage

I will be in the medical tent on race day keeping track of the environmental conditions, but we will be updating the site with live splits from the men and women as well as updates as the race unfolds.  After the race you can expect our normal analysis of the performances and pacing, so be sure to come back and also to join in the discussion!