Explain to me how it is the cardiovascular system knows what exercise the athlete is doing or is trained to do such that it knows to fail at different outputs for different exercises. That is a better argument for the central governor theory except neither one has a mechanism to explain how this "knowledge" is acquired by the cardiovascular system. You are right that the answer is integral to how the cardiovascular system operates except the cardiovascular system is reacting to systemic changes that are occurring from local failures peripherally. It is the only explanation that makes any sense to explain this variability.
How, again, does it explain this variability? What is the mechanism to explain the drop off in cardiac output at different levels in the same person near VO2 peak, depending upon how one is tested?
The question is not whether there is a VO2 max, clearly there is. The question is why is there a VO2 max (or peak if you prefer) and why is it what it is in any particular person being tested in any particular manner? What is the specific limiting factor that determines this number, be it VO2 max or VO2 peak?

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Frank,
An original Ironman and the Inventor of PowerCranks

Why is electrolytes the answer for cramping in triathlon??


Not true, everybody in any sport blames something else if things go not as planned.
Nobody will admit being not prepared sufficiently.
In ANY sport.
You may however be onto something with the cultural differences between continents ;-)

If you push to hard and go over your limits you go past the conditions your system is able to handle (ion balance or heat) your system will "shut down".
Cramping is just a sign of that. So, "electrolyte imbalances" are a good place to look, although taking electrolytes will in fact not substitute for proper training or taking PEDs.

Regarding top marathon runners: They barely sweat at all.
Much better adapted to heat stress (among other factors).

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Ego numquam pronuncio mendacium,
sed sum homo salvaticus

As a practicing ER physician - I'll say with 99 certainty that:

1) The doctors working the finish line are not idiots.
2) These same doctors can not judge blood volume or hydration reliably at all.
3) Most of these doctors don't know what a "tilt test" is and none ever do it.
4) If you studied a "tilt test" I assume it would be like "orthostatic vital signs" and in essence would be useless.
5) All the "patients" know that they are severly dehydrated and need an IV....99% of them are of course wrong. All of their family members agree with the patients. All of the non-M.D. people working the finish line agree with the pt. Some of the patients will pass out as you try to kick them out without an IV - they then will likely get at IV which will prove to all that the M.D. was wrong by initially refusing the IV and is actually an idiot.

Dave

5) All the "patients" know that they are severly dehydrated and need an IV....99% of them are of course wrong. All of their family members agree with the patients. All of the non-M.D. people working the finish line agree with the pt. Some of the patients will pass out as you try to kick them out without an IV - they then will likely get at IV which will prove to all that the M.D. was wrong by initially refusing the IV and is actually an idiot.

That's classic!

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Coach at KonaCoach Multisport

"1) The doctors working the finish line are not idiots."
"they then will likely get at IV which will prove to all that the M.D. was wrong by initially refusing the IV and is actually an idiot."

Wow, I hope I never get to visit your ER.... you make no sense.

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Ego numquam pronuncio mendacium,
sed sum homo salvaticus

The cardiovascular system doesn't need to "know" since it is only truly limiting when VO2max is achieved (see more below). VO2peak, OTOH, is limited by other factors (e.g., muscle fatigue that prevents the subject from sustaining exercise at a high enough intensity for a long enough duration for the cardiovascular system to be limiting).


No such mechanism need exist, because such a leveling off or even drop in cardiac output only occurs when a true VO2max is achieved. At that point, VO2 either plateaus or even declines, depending on whether or not it is possible to further increase a-vO2 difference. (Cf. http://www.ncbi.nlm.nih.gov/pubmed/12591751).

(BTW, while I'm citing references, here's another of Jose's studies directly refuting some of Dr. Noakes' claims, which he also conveniently chooses to ignore:

http://www.ncbi.nlm.nih.gov/pubmed/9824726)


As I said, VO2max is primarily limited by the cardiovascular system's ability to transport O2-carrying blood to the muscles.

Good Lord, how can you not get tired of this? You should make him take a test to prove that he has read something other than his 40 yr old Anesthesiology text.

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Steve

http://www.PeaksCoachingGroup.com

In addition to having the memory of an elephant, I have the patience of a saint?

Evidently.

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Steve

http://www.PeaksCoachingGroup.com

I wouldn't know the qualifications of the docs at the finish line at any particular race. However, if I were the medical director I would make sure that each of them were trained to distinguish these things (it is fairly simple) and that those with minimal experience were supervised by me. It is not the doc's job to treat what the patient thinks they need but to do a history and physical and, possibly, if necessary, some lab work, and treat according to what is best for the patient.

Where do you get the idea that orthostatic vital signs are "worthless" in this setting. I presume you would think pitting edema or temperature worthless also? All this stuff is part of the overall picture that the doctor needs to diagnose what is going on. If the patient walks into the medical tent it is unlikely that orthostatic vital signs need be done. If the patient was carried in, they probably should be.

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Frank,
An original Ironman and the Inventor of PowerCranks

As a (miraculous) survivor of heat stroke (I was not dehydrated, it was related to a medication I was taking), I have obviously done some reading on heat stroke and its causes! From what I have read, the original theory was that there was a continuum of heat illnesses -- from heat illness, to heat exhaustion, to heat stroke. An updated version is that, while heat illness and heat exhaustion are on a continuum, heat stroke is a completely different animal. Heat stroke seems to be much more a neurological thing, where the brain loses its ability to correctly regulate body temperature. So, while heat illness and heat exhaustion may indeed have a dehydration component to them, heat stroke in fact may not. Dr. Noakes, is this why you don't correlate dehydration with heat stroke in particular? I think that a clear delineation needs to be made between the two related diagnoses -- heat illness/heat exhaustion, and the separate diagnosis of heat stroke. It may be that on this thread people are interchanging these terms, and that may be causing some of the resulting confusion.

Just my $0.02.
Sharon

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Festina Lente

LOL. As I said, give me a mechanism for the leveling, and then, dropping off in cardiac output during VO2 max testing. Is it the filling volume is so large that the actin-myosin molocules loose coupling bonds? Is it the brain just can't take any more and turns on the vagus nerve and reduces contractility? Is it we have run out of capillaries and simply no more blood can be pushed through at that pressure? (wait, that doesn't explain the drop off).

Sez Dr. Coggan, trust me, I am a doctor, I don't need no friggin mechanism and, in fact, "no such mechanism need exist". LOL Ignorance is bliss.

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Frank,
An original Ironman and the Inventor of PowerCranks

I take it you don't need no friggin' mechanism either. Good for you. I will reiterate, ignorance is bliss.

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Frank,
An original Ironman and the Inventor of PowerCranks

Frank, you haven't READ anything about the CGM other than what Noakes has presented to you here. I'm sure you probably aren't aware of his debate with "the man" regarding the VO2max, since you haven't heard of the "catastrophic" model of exercise failure/exhaustion. You haven't READ anything about the limitations of exercise in the literature... at all. I've told you this before, you've been around a long time and if you don't have the gumption to go out and learn about these issue in the literature, I'm not going to take the time to spoon feed it to you. Andy's been doing it for years, and it still hasn't taken hold. He clearly has more patience than I do.

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Steve

http://www.PeaksCoachingGroup.com

Just give me a friggin' mechanism to support what he says about what is going on with the CV system at VO2 max.

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Frank,
An original Ironman and the Inventor of PowerCranks

No, you did not. What you said was:

"The question is not whether there is a VO2 max, clearly there is. The question is why is there a VO2 max (or peak if you prefer) and why is it what it is in any particular person being tested in any particular manner? What is the specific limiting factor that determines this number, be it VO2 max or VO2 peak?"

To which I replied:

"VO2max is primarily limited by the cardiovascular system's ability to transport O2-carrying blood to the muscles."

Now if you want to change the question to "what limits the cardiovascular system's ability to transport O2-carrying blood to the muscles?", that is all well and good, but it doesn't in any way undermine my earlier answer (as Aristotle pointed out in Posterior Analytics).

Anyway, to address your new question: the answer is still unclear, but it has been postulated that hyperthermia and tachycardia combine to reduce stroke volume.

As you have already in your sig line:

Exercise physiologists don't DO "mechanisms".

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Ego numquam pronuncio mendacium,
sed sum homo salvaticus

What I find ironic about Noakes' mention of the catastrophe theory of fatigue is that in introducing the term into the literature, Edwards emphasized that fatigue is a process, not an end-point.

No?

http://www.ncbi.nlm.nih.gov/pubmed/9277388

I just spent 45 minutes reading through this entire thread. Anecdotal or not, I think I'm still going to drink Gatorade, and I'm still going to utilize salt tabs when it's really hot out. From experience, I have found these to be beneficial (i.e., I delayed or avoided cramping). There may or may not be an element of placebo effect involved, but I'm ok with that if it's working for me.

Maybe, as Dr. Tim suggested, I'll stretch on occasion as well.

Thanks for the well thought out discussion.

mm

It seems to me that "specific limiting factor" goes beyond "cardiovascular system fails". You must be hell to work for always in your professorial one-upmanship mode. You are indeed the master of obfuscation. Anyhow, I am glad to see you don't really have a mechanism to explain this finding.

Anyhow, I have two questions for you.

1. hyperthermia occurs at VO2 max? How much? How fast?

2. Wouldn't a more reasonable hypothesis, other than "hyperthermia and tachycardia" be pH changes occur in the heart interfering with optimum metabolism and reducing contractility, causing the CO to level, then fall. We know that as we approach VO2 max that more and more lactate is produced which must be buffered, primarily by the bicarbonate system? This will drop the pH systemically and optimum performance of most enzyme systems occurs only in a very narrow pH range. Makes sense to me. But, what do I know?

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Frank,
An original Ironman and the Inventor of PowerCranks

I might add, that my hypothesis regarding the mechanism of the VO2 max limit doesn't require invoking any crazy central mechanism or place the heart at any specific risk by making it the limiting organ. The limitations come from simple, well understood, physiological principles.

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Frank,
An original Ironman and the Inventor of PowerCranks

Hey, at your urging I did a little search. Here is one thing I found. http://jap.physiology.org/...df_extract/106/1/343

If there were anything to this theory it would be able to be described in a couple of paragraphs here as to what the proposed mechanism is (I asked and got no answer) and one would suspect there would be substantial support for it in other laboratories by now. I guess not.

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Frank,
An original Ironman and the Inventor of PowerCranks

That could (almost) be considered .


Let me try:
I would call what you guys do "longitudinal research". Or some sort of two-dimensional line of analysis.
Whenever you get to a crossroad that sticks out of your plane of thought, you always cite "other unidentified factors", although it is well known that there are in fact very plausible and well researched mechanisms that would continue those dead ends and really support exphys data and make the "story" complete.

Reading Ex. Phys. work for me is always like:

yes! yeS!! yES!!!.....
Oh No! Almost made it!

But I really can't complain and actually appreciate the cartographic work, it since it gives us molecular "miners" some good incentive to dig deeper, and get a more three-dimensional picture of the land.
I also have no problem admitting that there are probably a couple more dimensions out there that researchers still miss with their work.

Personally I enjoy working with you guys, since it also gives the molecular studies a real life connection and very often, neatly explains certain physiological processes resulting from what we observe in our dimension.

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Ego numquam pronuncio mendacium,
sed sum homo salvaticus

Terra-man, good points about cramping in racing vs training. The 2 points that your bring up that I think are the most relevant are change of routine up to race day and "uniterrupted intensity on race day".

For the former I mentioned this on one of the Boston marathon threads to one of the guys that banged out a 1:15 half marathon in the midst of huge training block and then "relatively" tanked at Boston with a 3:12. He thinks his problems occur when the race goes north of 2 hours. I think the problem is not in the race being longer, but the fact that for all races over 2 hours (typically his A races), he goes into a full taper, changing his daily fitness routine, and throwing off his hormones. There is a reason Tour de France cyclists still train 2-4 hours on "rest days".

Dev