IM TX Temperature Impact on Run Pace
EN Team TX, My apologies( out of the country for the last 2 weeks) , I wanted to have this done for your race. For some reason I thought it was next week end. You all should be asleep at this time and will not see this until after the race so a last minute freak out will be averted. I hesitate to post his as it may cause some last min OMG impacts on a race plan. On the other hand for those that see this, added info may be of significant value. The EN WSM team doing research on the temperature impact on run has found that temp & humidity have a HUGE impact on run pace.
The cliff notes is the team has developed a view of the impact of heat on IM run pace. Below is a view of the % impact against your “best race date time” by temperature for the run. Note these temps are a different number than you see in daily forecasts, it is an impact composite of temp and humidity.
On this chartI have placed the forecast temp for IM TX run for tomorrow; it’s the second curve from the top. The top is IM LOU last year, the hottest IM so far, the team is in for a treat. The application that is in final stages of proofing will take your standalone Vdot and calc your “best day IM run time" and then show the impact of temperature on your pace. Then show the the resulting pace.
Below is a table I pulled together to reflect tomorrows temperature impact on a range of Vdots. You see that the impact at this temperature is significant! Consider these as BETA results – final review with the EN tem is needed,
Best of execution to all tomorrow – do everything you can keep the body temperature down. Ice sponges at every aid station!
Again please accept my apologies for being late with this effort. The team will get this finalized and rolled out in the next few weeks.
Matt
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Paul, Yes the temperatures charted are a specialized heat index that takes into account temp and humidity. This is not the National Weather Service heat index shown on many weather sites. The issue with the NWS heat index is the formula blows up below 70 deg F. Finding a stable heat index was one of many challenges that the team faced in this effort. The paper on the Schoen Heat index is here.
ftp://royale.aoml.noaa.gov/ocd/pub/gramer/thesis/2005 Schoen - A new empirical model of the Temperature-Humidity Index.pdf
The team is in the final stages of validating the resulting curves and completing an application that will allow an EN team member to drop in their relevant data and the app will spit out the % impact and resulting pace and estimated run time. When we release this for prime time, we will include a summary of the background behind the curves. We don’t want this to be a “Black Box”. I believe one needs to have a basic understanding in how the results were determined so that one can mentally say ok I understand this, boy I don’t like that fact that it is telling me to run XX sec per mile slower that I planned but by following this I will have another edge over the others out on the course.
very interesting data. I just finished the IM Texas event and your data is pretty good. I executed very badly (that's another story!), but I put my IM/Z1 pace somewhere around 8:25-8:30 and expected to run that pace. I ended up with about 9:30 miles for the day. Practically everyone in my age group went out fairly strong and just slowly died throughout the day. The weather was actually fairly good per the locals as we had overcast conditions most of the day. Had there been no cloud cover, the results would have been much worse.
tom
Tom, Congrats on a great race and Kona!
I went and pulled the actual temperature data for race day and the resulting average temp was cooler than the forecast from the prior day. Forecast average temp was 92.7 and the actual was 90.7 for the time you were on the run course.
Not sure if your really really smart or just backed in the data (I'm going with smart!), but my actual pace was 9:29 vs. your estimated best at 9:27. Wish I had seen this before the race. I had in the back of my mind the 8:25-8:30 numbers but thought if it was really hot, I'd have to add 15-30 seconds per mile. Your data suggests adding a minute. That's a big difference! I think everyone knows you need to slow down in the heat and humidity, but the amount you should slow down is quite amazing and I think it would take most people off guard.
tom
Yes the impact from heat is much bigger that one would expect. Prior to this work, I would have looked at the temperature impact tables in the Jack Daniels charts and for a 90 degree marathon it says you should add ~25 sec per mile. As you well know an IM marathon is a totally different beast that a open marathon. A key temperature impact difference is that in a open marathon you are starting with a cool body temp. In a hot IM you start the run with your body temp already close to redline. With the human body being ~25% efficient, running produces a ton of heat with very little cooling. When your core hits ~104 you stop no matter how motivated one is , a pro or a BOP AG. You can’t do a whole lot about added cooling, all you can do is produce less heat. If we want to run the whole marathon we must slow down a whole lot more than one would first expect.
PS – We had a SMART team working on this for multiple months. I was pleased to see the app forecasted your numbers well. When I drop my data in from IM Lou last year it projected a 4:28 run, I hit a 4:32.
Matt
I know that Tom Glynn was looking to run 8:15s on race day (he's run 8:39s at CDA), and he went 4:08 (that's 9:29s) to earn a Kona slot. Pretty consistent with the table above!!!
IM TX race team. We would like to use some of your data to check this application.
Once you adjust you time by the 9 seconds a mile for a 41:05 time and enter that in the top of the page you get the vdot of 50.3 and the temp table now shows at 75 degrees your actual run time os 42:00.
I know this may seem complicated, If you have difficulties send me your Vdot test distant, time and temp and I will rebase it to 60 degrees.
My last measured VDot test was 43 but based on training interruptions, etc. my best guess on Saturday is around 41-42. I'm not small (about 6' and 182 lbs) and live and train in Pennsylvania so was expecting to suffer in the heat and humidity so if anything I should be more affected by the heat. If it helps, my run started at about 3:45 PM and ended at 8:58 PM.
Based on your pre-race calculations, a 42 VDot would translate into a 5:13:46 marathon (11:59/mile). My actual chip time was 5:12:51 (11:56/mile)! That is amazing!! Less than 1 minute difference.
I didn't see your post until just now and so there was no even subconscious goal to hit this number, I just tried to keep "running" between aid stations (lots of ice!). I am still working on my race report but it appears that I paid for the 30 second per mile overage in the second half: first 13.1 in 2:30:30 and second in 2:42:21. I slowed but not too much.
Really amazing accuracy! I hope this data helps.
Matt,
Great work by you and the other team members on this one. Definitely some extremely valuable information here.
Gordon
Congrats to the team of WSM's on the app!
Look forward to seeing more data.
The application results are a 4:39:50 vs your 4:57. You said you went out to fast. Your thoughts on how you would have done if you had started at a 10:41 pace vs the 9:31 actual. Would that have put you on par with the overall time estimate?
The hope is that this data will help prevent people from heading out to fast for conditions. As you found out that makes for a challenging day! Great job getting it done on a HOT day.
Matt
Jeff my friend , I think you are still suffering from low blood sugar from the race
, the delta was only 17 min or 6%.
Matt,
Thought you might want to look at how things work at a lower end VDOT. My temp adjusted VDOT is 27.0. Unfortunately, for IMTX, I had some back problems that crept up during the race (as early as getting out of the water) and I really slowed down on the run, walking WAY more than my fitness would have allowed (IMO). I was shooting for ~14:10 pace. I got hold of some tylenol after the first loop and was able to hold that pace comfortably for about 8 miles. I'm fairly confident that absent the needles sticking in my back, I could have held on under 14:15-14:45 through to the finish. Of course, who knows? I'm just saying 14:15 felt really comfortable for the middle of the race.
Sorry no good actual data for you but you could plug in the 27.0 and at least see if what I was shooting for was good given the conditions.
it says that performance is not affected @ 60 or lower... is that the general consensus?
In my experience I run significantly slower in the cold winters than in the summer...Obviously some of this is due to wearing extra clothes and trying to avoid getting cold air in the lungs, but I still think that I run a good km/h slower in the winter simply because of the cold....
Anyone else expericen this?
Bo ... two things:
1. VERY FEW WTC IMs have been done over the past 12 years with run temps below the mid 50s - it almost never happens. So cold weather effects are a non factor, except in the Norseman, I guess.
2. When Matt looked at the performance curves related to temp, the times didn't start to rise until you got to 65-70F. A similar look at stand-alone marathons might show times starting to slow about 10 degrees lower.
Victor, Thank you for posting. You bring forward a new challenge for the application. I used the EM IM pacing table to pull “Best day race times” based on a Vdot. The trouble is the table stopped at a Vdot of 30. Please don’t take any non positive implications from this!! You are a part of the EN team and will get faster via Work Works!!!
Bo we looked at a broad range of IM races with temps all the way down to 51 degrees average for the run. We had 51, 52 and 53 degree average run races and they showed NO significant slowing compared to ~60 degrees. To Al’s point there are very few IM’s with those cool temperatures. “Conventional marathon pacing uses 60 degrees as the base line. We found this to be true. From a cold air in the lungs perspective having run many winters in upper MI and MN, I started to consider it to be cold at -10. Then I would focus on breathing in through the nose to have a longer path for the air to warm before hitting the lungs. I will say at these temps I was not running to a best time goal. As with most situations, time for acclimatization can make major performance impacts, be it hot, cold or altitude.
Matt