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S.M.

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 #1 
There was a marathon/half marathon where I live yesterday which was held in extreme heat and humidity.  While it's obvious that our bodies slow down in these conditions and it is advisable to not push the pace I can't find any specific literature that explains the mechanics of why.  Is it an O2 loading problem, an unloading problem or is it as basic as a redirection of blood flow away from working muscles to skin in an attempt to cool the body.  I had a number of runners that participated that were definitely slower than if it had been cooler however I had one in particular that suffered over the second half.  She was on top of her hydration and electrolyte needs (replacing 1/3 of what she was using) but her RF increased dramatically forcing her to walk because she was not absorbing what she was ingesting and continued up until about 30 mins post race when we could get her to lie down.  She kept saying she was hyperventilating but I really think that while her RF was high it was in response to an inability to clear the building CO2.  She was not dizzy or light headed, walked around for a while trying to calm her breathing.

My thoughts:  I don't really know.  I do know she struggles with low ferritin.  There is some inevitable dehydration while running regardless of temperature but more so when it is so hot and humid. Blood flow leaving working muscles to go to cooling, HR elevates to push thicker blood, can't digest because she is now working past her limiter so only burning carbs which in turn increases CO2.......

You can see by the graph that she made it through over half the marathon and about the time she starts to have difficulties is about the time they changed the course flag from green (everything is ok) to red (be careful, don't push the pace).

Stephanie Ottawa 290516.PNG 

Thoughts?



  

 
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Ruud_G

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 #2 
I think there are some good things already that you mention wrt performance in heat. Also look at this: http://sweatscience.com/tag/heat/ Also recently read a paper about the brain "taking into account" the heat and thereby regulating exercise intensity but couldn't find the paper quickly. Wrt the tHb. For some reasons a lot more fluctuation in after your comment. Did moxy let loose or move more?? SmO2 trends upwards something which might have to do with other muscle recruitment "taking off the load" of the place where Moxy was placed and less utilization on that spot. Just a few quick two cents
S.M.

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 #3 
Thank you Ruud I will read the link.  She did more walking later on particularly from 15:43 to 16:06 which interestingly the tHb is going down. She did mention that she would try to run and her breathing was laboured so she would walk off and on.  I have compared other graphs of hers regarding the absolute value of tHb and it seems relative.  I noticed post race when she was trying to calm her breathing that she was not belly breathing at all that it had switched to apical until I could get her lying down.  She also commented that she didn't "feel" the heat was an issue.
bobbyjobling

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 #4 
Reduced stroke volume and blood pressure? Maybe a lower plasma volume at the start of race then usual, eventually slight dehydratio + blood diverted for temperature regulations too? SmO2 drift's up due to reduced work.
S.M.

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 #5 
I agree, I think the SmO2 increase at the end was due to the lower work load as you can see the dip in SmO2 and tHb at approximately 16:08-16:10 is where she tried to run.

Interestingly this is that final attempt at a run then finish line, walking to medals and food all with higher RF.  
Stephanie Ottawa 2.PNG  If it was a removing CO2 problem we should see a vasodilation in the tHb which I kind of see for the first half of the effort; 16:07-16:10:45 ish but then tHb goes down until she stops and walks.  The huge increase in tHb at 16:14 I believe is an increase in blood flow due to her reduced effort.  I think reduced plasma volume and stroke volume are contributors.  What was the catalyst though?

bobbyjobling

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 #6 
I'm not sure but, It could be diet prior to race absorbing to much fluid from blood, intestine osmolaty.
http://www.ncbi.nlm.nih.gov/pubmed/9570264
S.M.

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 #7 
Interesting.  She did comment on a couple of days during the week that she was feeling bloated and not absorbing what she was drinking.  She knew in advance it was going to be unseasonably warm and was very attentive to her daily hydration including Nuun in all of her water.
S.M.

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 #8 
I came across this from one of Juerg's pp presentations.  It looks very similar to the last graph of Stephanie's (the blue line) which would explain potentially what was going on regarding her performance declining and even the increase in RF in response to her hypoxic situation.  
Stephanie example.PNG

I guess for me the question still remains:  does exercising in the humidity create an O2 loading or unloading problem or is it simply that more blood flow goes to the skin for cooling?  

ryinc

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 #9 
Old thread. My understanding is increased temp shifts diss curve right, resulting in easier unloading but more difficult.loading? So presumably lower Smo2 than would.otherwise apply, all.else equal?
bobbyjobling

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 #10 
This could be a problem for athletes that have limited O2 delivery or higher O2 utilisation as per some athletes performance at high altitude is reduced more then others due to same O2 delivery limitations or higher O2 utilisation.
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