The dew point in Mombasa today is 77 degrees

High Dew Point = Lots of mosquitos to spread the rampant malaria!!!!!!

malmo wrote:

Who could forget the NCAA's at Duke in the late 90s where one of the Hauser twins went from full stride to a blurry stagger in about ten meters, eventually collapsing, I believe, just short of the finish line. THAT was one ugly looking finish.

Excellent example. Wallace Wade Stadium's bowl can get nasty.

KevinM wrote:

The year in question 2000, and the incident prevented Stanford's third straight 1-2-3 in the 10,000.

I remember it was one of the first internet videos I've ever seen. Does anyone know how that race played out. I'm assuming Brent was "Frack," did he step across the line or roll across?

If anyone has access to the tape of that finish please upload it to youtube. As I recall, Hauser looked great until just before the finish, then all of a sudden his legs stopped working. You could tell he was in serious trouble.

I've run in a dew point of 77 degrees, and it was exhausting, even though I was only doing a distance run, not anything intense. That was after having a summer in which I ran in dew points above 70 quite a lot. I got used to up to 72 somewhat, but above that was still quite tough to run in.

So yeah. I would not want to jump in a plane in March and fly into that stuff to run what would be a very hard race in the best of conditions.

I think some people are more affected by the heat and humidity than others. Maybe I'm a pussy (probably), but I tend to suffer more than most in those conditions, and will choose not to race unless I have to. Even easy runs suffer in those conditions. My recollection of training runs at about 70F dew point is the same effort will yield a pace that's anywhere from 30-60s/mile slower than usual. I would imagine the effect on race pace would be similar.

Pete wrote:My recollection of training runs at about 70F dew point is the same effort will yield a pace that's anywhere from 30-60s/mile slower than usual. I would imagine the effect on race pace would be similar.

I dredged up some real data. In September 2006 I ran a half marathon in 67F DP. My time was almost exactly 6 minutes slower than what I'd run earlier in the year, although I was arguably in better shape. It wasn't windy. I remember clearly it was oppressively hot, and a couple of the leaders dropped out early.

So that was roughly 25s/mile slower for a half marathon in 67 dew point. That's one data point, anyway.

2001, not 2006. Doh!

Pete, aren't you an engineer? How big are you? The bigger you are the more difficult it is to dissipate heat.

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.

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11211124&dopt=Abstract

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]

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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]

or

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%.

malmo wrote:Pete, aren't you an engineer? How big are you? The bigger you are the more difficult it is to dissipate heat.

I doubt that skin area is the only important factor, malmo.

Here's one more data point. In June 2005, I ran a 10,000 in 62F dew point conditions (light to moderate wind) and ran 64s slower than a month before, again when in arguably better shape.

That's just over 10s/mile for 10k at 62 DP.

For your edification, a nice explanation why one should ignore absolute temperature and relative humidity in favor of dew point when talking about heat.

The Dew Point Temperature - A Better Approach

The Concept

Humidity is a complicated concept. Humidity refers to evaporated water substance in the air, i.e. water vapor. For years relative humidity has been what we use to inform the TV audience, but it has many pit falls and to tell you the truth almost no one understands it, including many meteorologists.

Think Energy

When thinking of humidity you always have to think in terms of energy. Of course this is expressed as temperature. There is only so much energy to go around and only a certain part of the thermal energy can go to do the work of evaporation. The rest goes to the other molecules in the air.

Relative humidity expresses how much of the available energy has been used. A relative humidity of 50% means half the energy has been used to evaporate water from the ground, streams, lakes anywhere else it is and 50% is still available to do more evaporation.

Relative to What?

On a summer morning the temperature may be 75 degrees and the relative humidity 90%, a very sticky morning indeed. Without changing the amount of water vapor in the air if the temperature hits 92 degrees in the afternoon the relative humidity is 52%. Relative humidity is RELATIVE TO THE AMOUNT OF ENERGY AVAILABLE Because the amount of energy increased as the sun warmed the atmosphere the percentage of the energy used decreased, i.e. the relative humidity, all the while there was no change in the amount of vapor in the air.

So when you hear someone say its feels worse than 52% relative humidity today, they do not understand the concept of RELATIVE HUMIDITY. Ninety-two degrees and 52% is a very humid afternoon. Because the concept is confusing many meteorologists are trying to get use dew point temperature.

The Dew Point Temperature

Dew point temperature is a measure of humidity. If you take a parcel of air, and cool it, eventually you will remove enough energy to begin to get water vapor to condense. Remember the water vapor was originally liquid water and to get it to evaporate you had to add energy. As long as it has sufficient energy it will remain vapor, but as you cool it at some point condensation will occur. The temperature where condensation begins is the dew point temperature. In terms of relative humidity, as the parcel of air is cooled, the relative humidity increases, when the relative humidity reaches 100%, you are at the dew point temperature.

Dew Point vs. R.H.

Unlike relative humidity if dew point increases, it is only because the amount of moisture increases. If relative changes it can be because of temperature change or moisture change, two variables leads to too many possibilities, with dew point it is strictly moisture you are tracking.

Dew point can never be higher than the temperature, at saturation, i.e. 100% relative humidity the temperature and dew point are the same.

So How Does Dew Point Feel?

On a typical summer day the following apply:

________________________________________

• Dew Point(F)..........Perception

________________________________________

• 75+....................Extremely uncomfortable

• 70-74...................Very humid, quite unfomfortable

• 65-69...................A bit uncomfortable for most people

• 60-64...................Ok for most, but everyone begins to feel the humidity

• 55-59...................Comfortable

• 50-54...................Very comfortable

• <=49...................Feels like the west, very pleasant, a bit dry to some

________________________________________

A Common Misconception

One last thing if you ever hear someone say it was 90 degrees and the humidity was 90%, that has never happened in Cincinnati, (and unless the greenhouse effect goes into overdrive never will). 90 deg/90% requires a dew point of 85.5 degrees. In Cincinnati the highest ever dew point was 81 deg. for just a few minutes.

In August 1995 we had four hours of 78,79,78,77 degree dew points, the highest persistent dew points I have seen in Cincinnati since working here as a meteorologist. For one hour I did see a dew point of 81, just after a thunderstorm.

World Record Dew Points

However veterans of the Persian Gulf War know what 90/90 feels like. The Persian Gulf and Red Sea both attain sea water temperatures in the mid 90's. That's plenty of energy, along with the 115 degree air temperatures, to evaporate water.

The dew point has been measured on the shore of Ethiopia, the area is now part of Eritrea, at 94 deg. F. The highest known dew point temperature in the world. The relative humidity with a temp of 115 and a dew point of 94 is 54% this doesn't tell you as much as the dew point when you consider the table above.

© 1995 Steven L. Horstmeyer, all rights reserved

Pete wrote:I doubt that skin area is the only important factor, malmo.

I don't believe that abstract said that. It's the surface area relative to the body mass that is the primary variable of heat dissipation. Obviously there's a genetic/metabolic component at work, but that's also being reflected in the aforementioned morphology. When it comes to heat dissipation and running, you can't teach small.

So in a nutshell Bekele will win again. He's in good shape (recent 2k indoor WR), he's a great XC runner (understatement), and he is one of the smallest guys running in the race.

malmo wrote: I don't believe that abstract said that. It's the surface area relative to the body mass that is the primary variable of heat dissipation. Obviously there's a genetic/metabolic component at work, but that's also being reflected in the aforementioned morphology. When it comes to heat dissipation and running, you can't teach small.

I wasn't disagreeing with the abstract (which I didn't read, to be honest), I was simply challenging your generalization after your "aren't you an engineer" comment.

I don't doubt being small (as I am) is an important factor (which of course you can't "teach"), but I suspect there are several other important factors (as there are with any complex system, like the human body) that could easily outweigh the importance of size.

Is Mottram running? It'll be interesting to see if there's any strong pattern in terms of who places better, relative to expectations, between the bigger guys and smaller guys. I suspect a clear pattern won't emerge. But it could be fun (for someone who likes stats - meaning not me) to see if any patterns emerge.

Pete wrote:

Is Mottram running? It'll be interesting to see if there's any strong pattern in terms of who places better, relative to expectations, between the bigger guys and smaller guys. I suspect a clear pattern won't emerge. But it could be fun (for someone who likes stats - meaning not me) to see if any patterns emerge.

Pete, Mottram is like Tergat, he has to run around in the shower to get wet. Heat dissipation shouldn't be any trouble for him normally. However, Mombasa doesn't quite fit into the "normal" range when it comes to heat.

malmo wrote: Pete, Mottram is like Tergat, he has to run around in the shower to get wet. Heat dissipation shouldn't be any trouble for him normally. However, Mombasa doesn't quite fit into the "normal" range when it comes to heat.

Well, then who would you expect do do worse in this heat? I don't think too many fatties will be toeing the line in Mombasa.

Malmo, Thanks for your various comments up and down this thread. A question about the temperature and humidity during the marathon. My guess is that the statistics you cite are based on when the marathons ended (presumably, when the winner crossed the finish line) and not when it begin. Yes? No?

malmo wrote:

wejo wrote:

Anyone know what the dew point was in Athens?

As I said there is often a mistaken perception when it comes to temperature and humidity.

M 10k 8/20/04 10:30pm 77 degrees 39% RH DP 55 degrees

W mar 8/22/04 6:00pm 86 degrees 58% RH DP 56 degrees

M 5k 8/28/04 9:00pm 75 degrees 38% RH DP 50 degrees

M mar 8/29/04 6:00pm 80 degrees 51% RH DP 54 degrees

Those are start time conditions. For the marathons, sunset comes into play, twilight radiation being much less than a direct overhead or rising sun that you would have on a morning start.Sunset womens marathon 8:07pm, mens 7:57.

Montesquieu wrote:

Malmo, Thanks for your various comments up and down this thread. A question about the temperature and humidity during the marathon. My guess is that the statistics you cite are based on when the marathons ended (presumably, when the winner crossed the finish line) and not when it begin. Yes? No?

malmo wrote:

As I said there is often a mistaken perception when it comes to temperature and humidity.

M 10k 8/20/04 10:30pm 77 degrees 39% RH DP 55 degrees

W mar 8/22/04 6:00pm 86 degrees 58% RH DP 56 degrees

M 5k 8/28/04 9:00pm 75 degrees 38% RH DP 50 degrees

M mar 8/29/04 6:00pm 80 degrees 51% RH DP 54 degrees

"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]

or

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%."

i dont know who you are..but i applaud your citation..

that said...this model doesnt seem to account for the fact that the increase in surface area relative to weight might be different depending on ones build...(e.a. how much that increase in weight is accompanied by an incrase in height?)

also there are other factors...in certain condition of extreme heat large size is an advantage...do basicly to heat capacity..

e.a. a camel can with satnd extreme conditions due to its size.

sorry that should be "thermal inertia"...not heat capacity

malmo wrote:

I think that most of you self-proclaimed tough guys should pay attention to the dew point this Summer. Hopefully we'll see a 70DP day or two and you can report back to me what you thought of your run that day.

malmo wrote:

How big are you? The bigger you are the more difficult it is to dissipate heat.

Haha, I just had a horrible run. Tried to do tempo run on the track at 4:30 pm, 86 degrees, 69 dew point. No shade obviously. Bad idea.

And I'm a big guy, 165 lbs.

Happened up this thread and loved these two comments.