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Discussion Starter · #1 ·
So....I have been reading and critiquing crappy student research papers all day and I can't do it anymore (some are good/but enough are bad to make we want to 'smack them')....

So I was doing some catching up on science.......

Alex Hutchinson Just posted this: Heat Stress, Plasma Volume, and the Benefits of Dehydration | Runner's World

Which reminded me of this: Produce you own EPO and increase Blood Volume by – | Steve Tilford

Which is discussing this study: Heat acclimation improves exercise performance

Which shows that short term (10 days) of exercise in the heat with mild dehydration increases plasma volume and thus Q (cardiac output).

Check out the figures in that study. Pretty dramatic increases in performance.

More recent data here: - Google Scholar

And a recent study here: Effectiveness of short-term heat acclimation for highly trained athletes - Springer

I have to re-wrap my brain around Coyle's early work on plasma volume and HCT changes.

"More importantly, Coyle et al. (4) stated that the potential for plasma volume expansion to increase Vo2max depends on the balance between the increased maximal cardiac output compared with the reduced hemoglobin concentration, and thus arterial oxygen content. The present study observed a moderate plasma volume expansion (6.5%) with a small hemodilution (3.3%) and increased maximal cardiac output (9%) and thus increased Vo2max by 5%."

Basically as you increase plasma volume, you increase preload via increased EDV. But you also dilute the HCT content per beat. Just infusing saline doesn't work (and is cheating) if you are trained. But heat is not a cheat.

So as Alex talks about in his blog....A tweak of heat training with some altitude AND some nutrition tweaks can lead to some pretty great performances.

Related.....Has anyone read water logged (Noakes)? I have it, but it is a FAT book that I have not dug into yet.
 

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Yep, PV expansion is pretty neat stuff. It is one of the first responses to endurance training and heat acclimation and only takes a few days before you start seeing significant expansion. It is also one of the first things you lose when you stop training. I recall a study done by coyle? (or perhaps convertino) a few years ago that looked at plasma volume contraction and loss of performance during detraining. Over the course of a few weeks of stopping training, PV and performance dropped significantly. The interesting thing about it was that they were able to restore a substantial amount of the lost training effect just by infusing saline and restoring PV back to "trained" levels.
 

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Discussion Starter · #5 ·
BUMP....

If you are in the Midwest, it has gone from being moderate to HOT. That 90 mile Road race in the 90+ temps and humidity was bad for me without much acclimatization.

Just thought I would bump this old thread.

{Still haven't dug into Water Logged by Noakes}
 

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BUMP....

If you are in the Midwest, it has gone from being moderate to HOT. That 90 mile Road race in the 90+ temps and humidity was bad for me without much acclimatization.

Just thought I would bump this old thread.

{Still haven't dug into Water Logged by Noakes}
This may be partially to explain why I perform so well under the hot July sun and weather. My best races have been in horrible hot weather, and I've never shied away from riding in the heat.

Interesting. I'll have to check out Water Logged too...
 

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I raced some crits last Sunday and then went to recon a hillclimb route on my way home. My garmin recorded a 105 degree average heat with 111 peak. That may or may not be accurate. All I know for certain is that it was *hot* out there. This may have been my hottest ride ever.




Forgive my weak power numbers. I was just cruising.
 

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This is very interesting and a bit counter-intuitive. I read this:

Which is discussing this study: Heat acclimation improves exercise performance

Which shows that short term (10 days) of exercise in the heat with mild dehydration increases plasma volume and thus Q (cardiac output).
I also read a couple of the citations in the article (the ones cited regarding increased plasma volume). Interestingly, one of the articles cited did not find an increased plasma volume. So, some discrepancy here.

What I was trying to ascertain was how you get an increased plasma volume with mild dehydration. I can kind of see water loss causing an increased Na+, causing fluid shift into the intravascular space, but I would think the intracellular water loss would impair cellular functions. Also, it is unclear what definition they use for "mild" dehydration.

Sdeer, can you shed some light on the mechanism for increased plasma volume and improved performance?

Anecdotally, I live in the Southeast and seem to perform better than most in the heat. I don't love it, but it doesn't bother me as much as others. That said, I've had some good results on hot days. Maybe training in the hot weather helped.
 

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I'd like to think acclimating to heat or cold is something most of us can do. I seem to do extremely poorly (moreso) when racing in a sudden dramatic change in temp. I once went from 100 degrees and humid to a rainy 60 degrees. Also went from a cool 60 degree spring to 90 at Joe Martin, which really sucked.
 

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It's perfect timing for this topic for me - 1 month out from RAIN and I haven't done any training in the heat, all my century rides this year have been done by 11am and it's never been above mid 80s for the finish. Definitely need to do some deliberate acclimating. Here's a timely article from CTS on the topic.

FAQs About Adapting to Training and Competing in Hot Weather - CTS
 

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Reading above & seeing stuff about the "Benefits of dehydration", especially in the context of a very hot training environment -- was a bit scary.

Reading the CTS linked article, it was good to see:
Should athletes restrict fluid intake in training to adapt to a lower fluid requirement for races in hot conditions?
NO. This idea circulates every few years, but it’s just plain bad.
 
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