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Friday, December 12, 2008

Top 8 of 08: Number 6

Number 6: Sammy Wanjiru in Beijing - too hot to handle

Number 6 on our Top 8 of '08 takes us back to Beijing to look a little more closely at Sammy Wanjiru's remarkable marathon victory in Beijing.

If you needed any reminder of it, Wanjiru became Kenya's first Olympic Marathon champion (in itself an incredible fact given the Kenyan dominance over marathon running) by scorching his way to a win in 2:06:32.

It was an Olympic record, one of the fastest marathons ever run, in a race without pace-makers, and most significantly of all, in hot and humid conditions. The graph below shows the splits from the race, for those who missed it.

There are many reasons why this run was so spectacular, both as a spectator and from the scientific point of view (which is, after all, the theme of this Top 8 series).

The pacing - last man standing

Firstly, you'll notice that the pace early on was almost on world record pace. Given that the temperatures were at least 10 degrees higher than is usually the case for the elite marathon runners, combined with high humidity, this was aggressive front-running the likes of which we've never seen.

The result is seen in the overall pacing strategy of the race - only one athlete in the whole race managed to run a negative split. That was an Italian who came 15th in a 2:14 time.

Wanjiru was the best of the top 10 men - his first half was run in 62:34, his second in 63:58, a difference of 1:24. That's huge for men at this level, who normally run close to even pace, but consider that Wanjiru's rivals were blown away by almost three minutes, and you realise that the Beijing conditions were so tough that the best runners in the world lost five or six minutes in the second half of the race. Incredibly, the average difference between first and second halves for the Top 10 was 4:03, testament to the conditions and the brutality of the pace set by Wanjiru (and Martin Lel, who is one of those who faded in the second half, finishing fifth)

The heat - physiology to the fore, Las Vegas style

But that is not the reason that Wanjiru's performance scoops our sixth place of Top 8 moments.

Rather, it's because Wanjiru's win was, from a physiological point of view, proof of an observation we've made a few times here on The Science of Sport - the smaller you are, the better you'll go in the heat.

Obviously, Wanjiru is a world class athlete, perhaps the next world record holder in the marathon. His 2:06:32 in Beijing is, in my opinion, the best marathon ever run, better than what Haile G would go on to do in Berlin in October. So Wanjiru is likely to have won no matter what the conditions - hot and humid, ice-cold and windy, Wanjiru seems the class act.

But what was most interesting to me, as a scientist, is the role that Wanjiru's small size played in his victory - weighing in at only 51kg, he was one of the smallest men in the race. And size matters in the heat. You'll recall that when the body temperature rises above 40 degrees, the athlete stops running - this is the "limit" to exercise, and so if that athlete wants to finish the marathon, they must run slowly enough to prevent their temperature from hitting 41 degrees before the 42km mark.

We can calculate the increase in body temperature that would be expected if an athlete runs at a certain pace on a certain day, using mathematical models. There are theoretical predictions, of course, and should not be taken literally, but rather to illustrate a point. Take a look at the following graph, which shows the maximum possible distance that can be run at different marathon paces for two different athletes, one weighing 60kg (blue), the other 70kg (red).

It should be immediately obvious that the smaller athlete, shown by the blue bars, is able to run further before they hit that limiting core temperature - for example, at 2:08 marathon pace, the 60kg athlete can run for just over 38 km, the 70kg athlete would make it about 30km before having to stop and cool down.

One can work out the fastest possible time that the athlete can run and still finish 42.2km. For the 60kg runner, it is about 2:10:20. For the 70kg athlete, it is 2:18:22. Again, this is not exact, because the mathematical equations don't provide exact guidelines, only illustrations of the key principle. That principle is that the larger athlete will overheat sooner on a hot day, and therefore must run slower in order to finish the race. This difference is enormous - 8 minutes thanks to 10kg of extra weight.

Now, enter Sammy Wanjiru. At 51kg, he was one of the smallest men in the race - the second smallest, if my searches were correct. Using the same formula we have above, we can work out that the theoretical limit for Sammy Wanjiru would be a 2:05:45, which means he is right on that limit, but still inside it. What he did in Beijing is therefore spectacular, impressive, but still physiologically predictable.

So predictable, in fact, that you'll find quite a nice tight correlation if you look at the order of finishers plotted against the mass of the runner. Sports science, Las Vegas style, says that if you want to place a bet on the winner, go first for the smallest runner, and then work out which small man is likely to be the best. The smaller guys tend to be better in the heat. In cooler races, this is not as significant (for other reasons, smaller athletes do tend to dominate running - this dominance is even greater in hot conditions). Just for the record, the smallest man in the race was Tsegay Kebede, of Ethiopia - he weighs in at 50kg, and he came third! Gharib, I believe, comes in at 56 kg.

So Sammy Wanjiru scoops position number 6 on our Top 8 list, thanks to his excellent demonstration of a principle of physiology. He happens to be an incredible runner too, and 2009 might just see him find his way onto the list as well, if he can get the right race on the right day, with the right pacemakers, because he's good for that world record.

Enjoy the weekend, and join us next week for the Top 5!



Andrew said...

The last plot illustrating the effects of mass is amazing! Would you be willing to expand on it? In particular I have a few questions:

1) Is the plot normalized with respect to temperature, or is it only one dataset at a given temp? I'm curious if the slopes for the runners change with respect to each other at different temps.

2) If so, is there a cold enough temp where the effect of mass is negligible?

3) Would you reproduce the plot with more masses? As a 90kg runner I'd like to quantify my whining when a little bugger outruns me. :)

Anonymous said...

2) If so, is there a cold enough temp where the effect of mass is negligible?

Yes. Stimulants are used to increase the body temperature in cycling’s Spring Classics for example.

Ross Tucker and Jonathan Dugas said...

Hi Andrew

Sure, no problem. I'll gladly send you the graphs - we have them for all masses up to 120 kg (we did a study recently looking at it - it was the Rae, Tucker et al. paper I referred to in our heatstroke posts in early November).

To answer your questions - those calculations are done for the conditions in Beijing at the time, which were temperature of 26 degrees, humidity 70%. Obviously, there's an error in that because both temperature and humidity would have changed throughout the race. This is one reason why I'm at such pains to emphasize that the calculation is only a guide, not meant to be prescriptive.

As for the slopes, they do change very slightly, but the principle remains - the smaller guys get hot slower than bigger guys.

This leads into your second question - there is very definitely a temperature at which this thermoregulation effect is no longer significant. It depends on size and running speed, making the interpretation of results quite complicated, of course

However, below a temperature of about 18 degrees, there is no theoretical limit for anyone weighing less than about 100 kg to overheat when running at 3min/km. It gets complex, because we still get hotter (body temperature rises, even when you run in the middle of winter, for example), but the point is that this theoretical limit doesn't exist below about 18 degrees celsius.

Above this, the bigger guys who run really fast have theoretical problems, but a 60 kg athlete is still fine. Only when it starts to hit the high 20's (above 26 degrees) does the theoretical limitation start to enter the picture, as shown in the graph - he can no longer run world record pace without running into trouble early.

Again, I must emphasize that this is theoretical - some famous research showed that body temperature is also predicted by relative intensity - in otherwords, it's not quite so simple as the big guy and small guy running at the same speed and the big guy gets hotter. It depends also on what that speed is relative to their maximum. However, for the current situation, comparing only elite athletes, the comparison more or less works. However, if you compare me (at 80kg) with an elite athlete at 80kg - I'll generate a lot more heat running at 4min/km than him, because it's relatively faster for me.

It gets quite tricky, but it does make a really important and prettyc oool point.

It is definitely something I'll post on in the future - perhaps bear with me for the rest of this year, because i have to finish this Top 8 Series, then it's Christmas and New year. But first thing in 2009...

But if you want to send an email address, I'll reply...


Giovanni Ciriani said...

Just taking into account the physics of heat rejection: the lower the temperature the more heat a smaller athlete will be able to shed per unit of weight, compared to a larger athlete. The paradox is that, in unbearable heat conditions, a larger athlete will last longer than a smaller athlete before getting a heat stroke. I base this observation on this simple physical fact: an athlete 1% shorter will have 3% less mass, will have to produce 3% less energy, but will have 2% less surface to shed heat, and will have a 1% advantage (3%-2%) in shedding it. Therefore since the advantage is proportional to the temperature difference (Tbody-Tambient), the advantage will get larger at lower ambient temperatures. Vice versa at Tambient temperatures above Tbody, where the goal is to stay cool as long as possible, a smaller athlete will absorb heat from the ambient faster, and a bigger athlete should last longer than the smaller athlete before being overcome by the heat.
Giovanni Ciriani

Anonymous said...

GMC, I'm wondering whether the relationships between heat generated, heat loss and surface are are linear, linear such that you are arrive at a 1% advantage by subtracting 2% (made on surface area) from 3% (made on mass).

Anonymous said...

G'day Ross,

Do you think there would be any value comparing orthodoxly clad marathon runners with those as close to nude as sensitivies permit?

On the other hand (thinking as I write), a form of cladding, with the ability to enhance the evaporative cooling effect (especially after periodic dousing with water or some other permitted cocktail), might be a productive direction to consider.

David Calvert

(regret I don't understand all the identity URL stuff below)

malmo said...

You're balancing heat production, which is proportional to body mass, against heat dissipation, which is proportional to surface area. Since mass(volume) increases with the cube of the radius, and surface area only increases with the square of the radius, it should be clear that weight (and heat production) will increase faster than the heat dissipation properties afforded by surface area.

Additionally, much of heat dissipation occurs in at the top surface of the body, the head and shoulders, which also contains the organ of the body (the brain) which is most affected by heat.


Advantages of smaller body mass during distance running in warm, humid environments.

Marino FE, Mbambo Z, Kortekaas E, Wilson G, Lambert MI, Noakes TD, Dennis SC.

Human Movement Studies Unit, Charles Sturt University, Bathurst, NSW, Australia. fmarino@csu.edu.au

The purpose of this study was to examine the extent to which lighter runners might be more advantaged than larger, heavier runners during prolonged running in warm humid conditions. Sixteen highly trained runners with a range of body masses (55-90 kg) ran on a motorised treadmill on three separate occasions at 15, 25 or 35 degrees C, 60% relative humidity and 15 km x h(-1) wind speed. The protocol consisted of a 30-min run at 70% peak treadmill running speed (sub-max) followed by a self-paced 8-km performance run. At the end of the submax and 8-km run, rectal temperature was higher at 35 degrees C (39.5+/-0.4 degrees C, P<0.05) compared with 15 degrees C (38.6+/-0.4 degrees C) and 25 degrees C (39.1+/-0.4 degrees C) conditions. Time to complete the 8-km run at 35 degrees C was 30.4+/-2.9 min (P<0.05) compared with 27.0+/-1.5 min at 15 degrees C and 27.4+/-1.5 min at 25 degrees C. Heat storage determined from rectal and mean skin temperatures was positively correlated with body mass (r=0.74, P<0.0008) at 35 degrees C but only moderately correlated at 25 degrees C (r=0.50, P<0.04), whereas no correlation was evident at 15 degrees C. Potential evaporation estimated from sweat rates was positively associated with body mass (r=0.71, P<0.002) at 35 degrees C. In addition, the decreased rate of heat production and mean running speed during the 8-km performance run were significantly correlated with body mass (r=-0.61, P<0.02 and r=-0.77, P<0.0004, respectively). It is concluded that, compared to heavier runners, those with a lower body mass have a distinct thermal advantage when running in conditions in which heat-dissipation mechanisms are at their limit. Lighter runners produce and store less heat at the same running speed; hence they can run faster or further before reaching a limiting rectal temperature.

PMID: 11211124 [PubMed - indexed for MEDLINE]

For purposes of thermal comfort analysis, skin surface area can be estimated using the following formula (the Dubois surface area):

A= 0.202*M^0.425*L^0.725

Where A is surface area [m^2], M is mass [kg], and L is height [m]


A= 0.108*M^0.425*L^0.725

Where A is surface area [ft^2], M is mass [lbm], and L is height [in]

According to this scaling law, doubling weight increases skin surface by 34%.