Clearly without a powermeter to provide quantitative feedback, you have no clue whether you were at or exceeding your fitness on that day. The cramps could have been due to the alignment of the moon and the sun. Without a powertap, you have no proof.

LOL

In bike road racing when the big break goes or the big acceleration comes, it does not matter what the Powermeter says or the heart rate monitor reads. You have one simple and clear goal - do EVERYTHING you can to stay in the group. I like road racing for it's clarity in this regard. If you don't make the break, your day is done!!

I actually looked at the cramps as a reward for hanging on till the end of that race. I knew I would never win a field sprint, but I had a reat time!

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Steve Fleck @stevefleck | Blog

Maybe God watches over each of us and keeps us from exercising too much. Look at all the athletes who thank God as they cross the line (presumably for keeping them from killing themselves during their extraordinary effort). Seems like pretty good evidence right there. Just as plausible don't you think. Just don't ask me to tell you how he intervenes (or why) or to prove it.

There are much simpler explanations that don't involve the brain and involve known physiological principles.

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Frank,
An original Ironman and the Inventor of PowerCranks

Actually, I wasn't taught those in school at all. If I was, I forgot them. I learned them during anesthesiology training. I learned them because we used them almost every day. These "tricks" are a way of quickly assessing the fluid status of a patient to determine how to best safely proceed. Is the patient safe for the procedure and chosen anesthetic technique or does one need to delay things to rehydrate or place additional monitors, central lines, etc. Most anesthesiologists are pretty good at it and, while not perfect, I would say we "guess" pretty close to correct about 98% of the time.

Everything must be put into perspective. Is there pain? Is the problem acute or chronic? Is the patient old or young? What is the condition that brings the patient to you? It is not some dogmatic rule passed down by old fogey's but useful clinical evaluation tools to help the clinician do his job well. But, they require skill and experience to be applied well. Without them, the choice for the clinician is to either "guess" or to monitor everyone to the max, increasing risk and delay.

Every test, be it a physical exam "test" or a laboratory test or an xray has the ability to have false positives and false negatives. That is part of the job of the clinician, to learn how to interpret those tests. Some clinicians do it extremely well, some don't. Most are pretty good (edit: at least with the stuff they use regularly).

Earlier I was told there was no reason to ever do an orthostatic blood pressure test because most of the people were hypotensive flat on their back. I am not sure what he means but I know many people whose normal BP is 85-90/55-60. Where others have normal BP's in the 140/90 range. I simply don't know how to interpret on the basis of a single reading whether a bp of 90/60 is completely normal in person A or is substantially hypotensive in person B. I guess if there are enough other signs to suggest one thing or another then maybe I wouldn't sit them up and repeat the BP (It doesn't take much time, all I look at in this situation is when the needle starts bouncing, no need to take the entire pressure, although I can get diastolic without using a stethascope in most instances also) but one reading in isolation doesn't mean much to me.

Temperature per se has no direct correlation with fluid status but I would be extra observant of someone in whome their initial temperature was 103-104. I would want to make sure it was going down, not up. And, it might determine how aggressive I was in treatment.

Your criticism of my comments suggest to me you simply do not have much experience in using these tests. You say, I would expect this or that. Well, so would I. Anything different from what I expected would give me pause. That is the whole idea of doing an exam, to confirm or refute your initial clinical assessment.

I personally think it is pretty easy to tell on physical exam who is significantly dehydrated and who is not. That was part of my job in the operating room and I tried to teach medical students and residents how to do it also. Nobody is ever 100%. That doesn't mean we can't be very good. I don't see how it is much different just because the venue moves to a finish line.

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Frank,
An original Ironman and the Inventor of PowerCranks

Maybe that's why you didn't break 9:00...

:-)

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"Go yell at an M&M"

You are correct. These authors (and others studying US soldiers performing similar studies during World War 2) noted that the psychological effects of not drinking were much greater than the physiological effects but that recovery was very rapid when "dehydrated" subjects were given fluids to drink by mouth (note - not intravenously). The results are reported in the monograph by Adolph published in 1947.

Maybe it's God and maybe it's just our brainstem overriding our cortex. ("cortex you may be smarter, but we primitives down here in the brainstem and midbrain have final control.")

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Dick

Take everything I say with a grain of salt. I know nothing.

Perhaps. All I asked for was a mechanism to explain how it would work.

It is clear that a lot of the evidence that is being used to support this governor theory is simply showing that the mind can have effects of submaximal efforts. I actually believe that without needing to see any studies in support. If someone claimed otherwise I would ask to see their study data. However, the theory here is the brain is regulating the maximum effort. I see no evidence to support that theory and no one can give me a mechanism as to how it might work. That is all.

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Frank,
An original Ironman and the Inventor of PowerCranks

Study of modern hunts by the !Kung San hunters in the Kalahari Desert in the last decade especially by my South African college Dr Louis Liebenberg show that the factor which determines the duration of the hunt is the time for which it it really hot. Thus a modern hunter will only run down a large antelope (Eland or Kudu) if he has 4-6 hours of extreme heat (40-46 degrees C/104-114 degrees F) in which to do it. So the hunt will begin at midday (when it is starting to get really hot). Once it cools down in the late afternoon (4-6pm), the antelope will be able to cool down and will not be caught (since it is the high body temperature of the antelope which causes it to become essentially paralyzed and then possible to be speared at close range with no risk to the hunter).

Most of these hunts cover less than 30km. So perhaps it is the length of the midday heat that has something to do with the exercise duration for which we might be particularly well adapted.

@dr. noakes -- could you comment on fleck's point about cramping during races, which seem to be a result of effort and not dehydration? i've had similar experiences in road races where dehydraton doesn't seem to be the culprit.

An interesting observation. It would seem that is really doesn't make much difference how one is specifically adapted as long as one is better adapted to their prey for certain conditions. I would assume it was a trial and error effort that allowed these tribesman to figure out what their prey should be and how to hunt to take advantage of their advantage. If we had slightly different water/salt conserving mechanisms I presume those tribesmen would be hunting different prey or hunting this prey in a different manner.

Interesting. Thanks for that.

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Frank,
An original Ironman and the Inventor of PowerCranks

Thanks for confirming that. All these things would suggest that the brain's anticipation of replenishment or sensation in the mouth of same, is enough for it to allow us to proceed (to try to kill ourselves.)

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Dick

Take everything I say with a grain of salt. I know nothing.

To take it a step further, I can have cramping on a very short high intensity set of step ups, lunges, calf raises, hamstring curls, or squats...and all of these have nothing to do with hydration or electrolytes.

For me, the higher the intenisty, the higher likelihood of cramps.

If the duration is really short, I need really high intensity to bring about cramps. If the duration is long (ex Ironman), then the intensity can be reasonably low.....seems like cramps are proportional to the intensity-duration product if you want to map it on a 2 d grid. Then I suppose you can make it a 3-D model by adding in hydration and then making 4-D by going with blood sodium level.

Now someone go and do the 2nd derivative of each 3-D surface on the 4-D space to show us where cramping is about to happen :-). While we're at it, program that into the powertap to warn us 2 minutes before aforementioned cramps that they are about to happen.

Seriously though, I think the entire discussion has been great, but cramping has to be related to a combination of intensity, duration, electrolytes and hydration, cause we all know from real life that they occur when a combination of these factors are present.

Dev

They probably are also associated with your genetic make-up and predispositions. Finding a "one-size-fits-all" solution to this problem, I suspect, isn't going to happen.

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Frank,
An original Ironman and the Inventor of PowerCranks

As I think about this an interesting area to research might be to do a genetic comparison between athletes who have a lot of cramping problems and those who don't. Perhaps one could find some markers that show who is susceptible and then determine how those differences are reflected in the body which might give those who are susceptible better strategies for avoiding same.

I don't know who would pay for such a study but it would be interesting if it could be done.

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Frank,
An original Ironman and the Inventor of PowerCranks

Maybe that's why you didn't break 9:00...

Ken,

That's it!! :)

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Steve Fleck @stevefleck | Blog

This industry-funded study was conducted in a laboratory that did not have proper convective cooling (wind speed). When we repeated the study in our laboratory which has a properly designed wind tunnel to insure that cyclists working hard in the heat did at least get the benefit of a decent facing wind speed as occurs in real world exercise, there was no difference in the rectal temperature of those who drank either the equivalent of "ad libitum" or "as much as possible" (A.Sanders et al. Acta Physiol Scand 2005). Thus the higher temperature in the "dehydrated" state was simply an adaptation that the body made to try to increase its heat heat loss without the need to sweat more when the environmental conditions in which the study was undertaken were sub-optimal.

This is a well-known phenomenon in free-living desert animals. The best way to regulate your body temperature at rest or during exercise is to allow your body temperature to rise. This is a water-conserving mechanism. The best example is the desert dwelling Oryx which allows its body temperature to rise to 46 degrees C when it has no access to water. When water is available, it will maintain a lower body temperature by sweating (until such time as it no longer has access to fluid). Similarly during exercise the African hunting dog maintains a higher body temperature than domesticated dogs. This allows the wild dog to run further with less water loss even though they are hotter. The African hunting dog has the highest hunting success rate of any African predator. Seems like running with a higher body temperature might be quite a good choice and not a sign that the animal is about to die from heat stroke.

Of course what the industry never wanted anyone to know about this study was that despite exercising at high intensity for 2 hours in quite extreme heat (33 degrees Centrigrade) with high humidity, none of the subjects became ill because they did not drink at all during the 2 hour exercise bout. Nor did they want you to know that the body temperatures of those who did not drink were not particularly high at the end of exercise (approximately 39 degrees C) compared to values of at least 41 degrees C routinely measured in winners of 10,21 and 42km races who are without symptoms (other than the emotional high of winning a race). Nor did they want you to know that there NO difference in the body temperature responses in the first hour of exercise between those who drank "to replace all their sweat losses" or who drank nothing. Nor did they want you to know that the difference in rectal temperature response between those who drank "ad libitum" and those who drank "to replace all their sweat losses" was about 0.5 degrees C, a biologically insignificance difference.

Nor did they want you to know that this study was designed to develop the highest possible sweat rates during exercise so that these could then be applied to everyone who exercises whether at high or low intensity or in the heat or the cold. This study formed the basis for the 1996 ACSM guidelines which for the first time proposed that athletes needed to drink "as much as tolerable" during exercise or between 600-1200ml per hour. Of course when these guidelines were applied to athletes like Cynthia Lucero running the 2002 Boston Marathon in 5-6 hours in a temperature of 10-12 degrees C, they were totally inappropriate since her sweat rate under those conditions were probably closer to 200-300ml per hour.

So please don't quote this study to me as evidence that dehydration causes heat stroke. This study and the way it was interpreted was the principal cause for the global pandemic of EAH that began shortly after the adoption of the 1996 ACSM guidelines.

Also sweat rate is regulated by the sympathetic nervous system not by cardiovascular system. Thus for the sweat rate to fall during exercise requires a change in the sympathetic supply to the sweat glands. Again why would the brain choose to reduce sweating if this would cause heat stroke to occur knowing that this effect must also kill the brain? Logically the brain would only choose to lower the sweat rate if there was some logic to this choice (as occurs in the Oryx in the desert).

There are new data (in review in the scientific press) showing that weight losses in excess of 3% in marathon runners in real competition are not associated with body temperature elevations in excess of those that would be predicted from their running speed (exercising metabolic rate). Some of these runners reached levels of dehydration of up to 10%.

Events that occur at the same time may not be causally related. To develop a level of dehydration in excess of 3% you have to exercise for longer. The longer you exercise, the more tired you become and the closer to a (non)catastrophic failure. The fact that you enter a "danger zone" when you develop a weight loss of 3% may be simply because that is the duration of exercise at which your brain begins to find another reason why it should slow you down (ie muscle and liver glycogen depletion amongst many other possibilities).

Of course it is much easier to explain the complex phenomenon of fatigue on something that is easy to understand (ie dehydration) especially if that is all you ever read about in threads like this and in the adverts of those industries that benefit most from your believing this simple explanation (and for the cure of which surprisingly they provide the sole cure).

Sweating can be caused by the nervous system but I am unaware that it can be turned off by either the sympathetic or parasympathetic nervous system. Beta blockers, which can stop "nervous sweating", will not stop sweating during exercise.

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Frank,
An original Ironman and the Inventor of PowerCranks

These data would predict that your wife has adapted to a low habitual salt intake like the Kenyan runners that we studied. What appears in the sweat is the dietary excess that has not been excreted in the urine and has nothing to being a "salty sweater". Salty sweaters are simply salty eaters (and this includes those with the gene for cystic fibrosis. If patients with that condition - which causes higher than normal sweat sodium concentrations - were not eating a high salt diet they would very rapidly die from salt deficiency). The reason why the scientists supported by the sports drink industry have yet to discover this surprising truth is because they seem not to understand that if you wish to study sodium balance in humans you cannot do so simply by measuring the salt content of sweat. You need to analyze urinary losses and habitual dietary intakes as well.

So when you see reports of "salty sweaters" (apparently the sweat of Tiger Woods and Maria Sharapova amongst many other stellar athletes has also been tested to determine whether or not they are "salty sweaters") just ask what was their urinary sodium losses and their dietary sodium intakes before concluding that they are "salty sweaters".

Dr Noakes, thank you very much for your contributions.

Can you offer any insight into 'night cramps'? Those brutally painful calf cramps that wake you up from a dead sleep. Or the dreaded 'just woke up - yawning - stretching - calf cramp' that has been severe enough to cause me to limp for hours.

Thanks

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"Competetive sport begins where healthy sport ends"

Of course not because beta-blockers do not block the specific sympathetic nervous system messenger (acetylcholine) that causes sweating.

I found this at http://www.diagnose-me.com/cond/C511064.html

"Two different sets of nerves supply these many glands: the sympathetic nerves, which tend to increase sweating when one is excited, nervous, or afraid (the "fight or flight response"), and the parasympathetic nerves, which tend to decrease sweating of the skin. At the ends of these nerves, the body releases special chemicals called neurotransmitters, which carry the electrical signal from the nerves onto the cells near the nerve endings. For the sweat glands, the chemical at the tips of the sympathetic nerves is acetylcholine; too much of this chemical present next to the sweat glands stimulates them to produce large amounts of fluid".

Well, I am unaware that sweating is fully dependent upon an intact sympathetic nervous system. Sweating is induced to collect seat for sampling to diagnose systic fibrosis not by stimulating the sympathetic nerves but by simply heating a small area of the skin to induce blood flow to that small area, which causes sweat that can be collected.

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Frank,
An original Ironman and the Inventor of PowerCranks

First off I can't find the Sanders article in Acta Physiologica Scandinavica anywhere printed in 2005...but found it under "Saunders" finally:
http://www3.interscience.wiley.com/...l/118680040/abstract
"On five occasions nine subjects cycled for 2 h at 33.0 ± 0.4 °C with a relative humidity of 59 ± 3%. Air velocity was maintained at 0.2 km h−1 (0 WS), 9.9 ± 0.3 km h−1 (10 WS), 33.3 ±2.2 km h−1 (100 WS) and 50.1 ± 3.2 km h−1 (150 WS) while subjects replaced 58.8 ± 6.8% of sweat losses. In the fifth condition, air velocity was maintained at 33.7 ± 2.2 km h−1 and subjects replaced 80.0 ± 6.8% of sweat losses (100.80 WS)."

Okay, so you replicated the test using a windtunnel that provides substantial convective cooling...and concluded that except at low velocities (0, 10km/h) body temperature was consistently regulated. At 20 and 30mph I would expect this to be the case when the ambient temperature was 33C (91.4F) and less than core temperature...i.e. providing a substantial cooling effect through convection as mentioned in the results. At running speeds (10km/hr) shockingly body temp and PE was higher...big surprise. Maybe you can enlighten us as to the total percent of dehydration of the subjects in the 58.8% replacement...since it isn't specified in the abstract. For instance, at 1.9L/hr sweat rate if I replaced 1.1L/hr after 2 hours I would not be significantly dehydrated, having lost only about 3.4lb bodyweight (2.1%) and would not have any noticeable symptoms of dehydration. At the moment I would have to say your study is interesting and useful but ultimately does not contradict the earlier study. What this study shows is that subjects with mild dehydration and high windspeed fared the same as subjects with very little dehydration and high windspeed...and those with mild dehydration and low windspeed (running) were significantly higher in temperature. I could have guessed those results without the test, but having actual numbers on the effects is always good.

BTW-extreme heat 33C/91F? I run in that temperature every day in the summer!

Actually I did think of one other possible reason that I have issues with high temperatures and excersizing...my normal resting body temperature is marginally higher than normal at 99.4F/37.4C...I wonder if this could have something to do with it. Maybe I am 1F closer to overheating than the normal person...?

My take on the change in sweat rate is that the mind is simulataneously shutting down the body's ability to excersize at high intensity while slowing down (or nearly stopping) the sweat rate in order to conserve water. This sounds exactly like what happens with the Oryx and seems entirely logical. Not great if you are being chased by a lion, but as a self-protection mechanism in extreme conditions it seems reasonable.

http://www3.interscience.wiley.com/...RETRY=1&SRETRY=0
"Consequently, average mean power output during the five sprints was lower in hyperthermia (558.0 ± 146.9 W) compared with control (617.5 ± 122.6 W; P < 0.05)."
As evidence of the above...power output drops when overheated. As you (or someone else) mentioned earlier, it may be possible to train this response, but looking at my training logs over the past years I have consistently gone 30-40s slower per mile in the summer heat (Floriduh sauna-like humidity) compared to winter (60F and 30-40% humidity). When I first started seriously running down here the summers were just brutal and I had to run in the early mornings and be done well before noon or I was toast. After a couple years of acclimatizing I can run noon-3pm in the mid 90s and 85% humidity without problems...as long as I am drinking enough water.

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Well, let me hypothesize a reason "why" the brain would choose to stop sweating despite that might mean hyperthermia. It is a matter of choosing the lesser of two bad alternatives. Stopping sweating will raise peripheral vascular resistance in an instance where BP is falling too low to maintain vital functions in the vital organs, the brain and the heart. It would do this to avoid immediate damage and take on the risk of possible later damage. Unfortunately, the conscious control the brain sometimes exerts doesn't always make the body stop doing the activity that caused all the problems in the first place. If the person would stop exercising when the sweating stopped there would probably be little risk of causing heat related damage.

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Frank,
An original Ironman and the Inventor of PowerCranks