Actually, you will be more down than that because you are forgetting insensible losses, those that occur from the huidification of the inspired air with each breath. This can be substantial depending upon the conditions. No electrolytes are lost this way, this is pure water so it has a smaller impact on the vascular volume than the sweat loss where sodium is lost also. But, it all adds up.

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Frank,
An original Ironman and the Inventor of PowerCranks

1. Fast running speed (high metabolic rate) which increases the rate of heat production.

2. High humidity and air temperature.

3. Genetic muscle disorder that may cause an even higher than expected rate of heat production (thermogenesis) and which maintains a high rate of heat production when the athletes has stopped running and for the correction of which the athlete must be placed in ice. If exercise alone was the cause for the excessive heat production then it would not be necessary to cool these athletes in ice AFTER exercise since the moment they stop running, their body temperatures would fall very rapidly (because they have stopped producing the excess heat and because of of a larger than usual gradient between their core temperatures and the air temperature).

4. Presence of some other factor that can activate excessive thermogenesis in the (genetically-predisposed) skeletal muscles. Drug use needs to be considered.

5. Failure of the brain to detect that a body temperature in excess of 41.5 degrees C will be reached before the expected end of the exercise bout. Normally the brain will cause the athlete to slow down and so maintain only that pace that will allow a temperature of 41.5 degrees C to be reached at the finish line.

6. Use of medication especially amphetamines that prevent the normal action of the Central Governor to slow the athlete so that heat stroke cannot occur.

7. Intercurrent illness causing exercise to begin with an elevated body temperature (greater than 38 degrees Centigrade) and to rise excessively during exercise.

8. Some factor interfering with sympathetically-mediated sweating causing impaired sweating and hence impaired heat loss.

To develop heat stroke you need a number of these factors to be acting at the same time.

Our study (Holtzhausen L et al. MSSE 1994) showed that most (~85%) athletes collapse AFTER they finish exercise so that dehydration cannot be a factor (since if dehydration causes collapse as a result of cardiovascular failure then it must happen when the athlete is exercising not when he or she has stopped exercising and the stress on the circulation is falling. Also we know that athletes with heat stroke collapse with high not low cardiac outputs showing that cardiac "failure" does not explain their heat stroke). Rather it is the act of STOPPING EXERCISE that causes these collapses, not the act of continuing exercise. We also showed that these athletes did not have higher body temperatures than the control group of runners who did not collapse after exercise. Thus the athletes were not suffering from "dehydration induced heat illness'. Next we showed that a majority of ultramarathon athletes develop postural hypotension (Holtzhausen L and Noakes T. MSSE 1995) suggesting that the more rapid onset of postural hypotension probably explained why some athletes collapse immediately they terminate exercise. Then we found empirically that treating these athletes by elevating their legs and pelvises above the level of the heart reversed all their symptoms. At the 2000 and 2001 South African Ironman Triathlons at which I was the Medical Director we did not use a single intravenous infusion to treat our collapsed athletes; instead we simply treated all collapsed athletes according to what we diagnosed to be the problem. It they had postural hypotension we simply treated them by elevating their legs and pelvises. In those races we also had the lowest proportion of medical complications in any Ironman yet reported (Sharwood K et al. CJSM 2002; BJSM 2004) and only one case of EAH encephalopathy in an athlete who ignored our advice to drink only to thirst (Noakes et al. BJSM 2004). There was no evidence that this model of treatment delayed the recovery of any of these athletes or that the advice that all athletes should drink to thirst during the competition was harmful to anyone's health.

This model of treatment has since been adopted by the International Medical Marathon Directors Association at all marathons directed by their members. Included in this group is the Berlin Marathon in which aid stations are placed only every 5km on the course (as also in the Rotterdam and Rio de Janiero Marathons). The Rio de Janiero and Berlin Marathon have amongst the lowest rates of medical treatments of any of the large city marathons. Which seems surprising if it is the prevention of "dehydration" that prevents marathon collapses. Rather it seems as if the opposite applies - the more fluid that is provided in marathon races (and perhaps also in triathlons) the greater the percentage of starters that will seek medical care at the finish.

I will discuss in a subsequent post the evidence that the level of hydration during exercise cannot be the explanation for the very high temperatures measured in athletes with heat stroke.

Not sure that either of these ladies died. Also their gait is very primitive suggesting that there has been a major change in brain function. My diagnosis is that they have an encephalopathy of unknown cause. What were their rectal temperatures? If elevated above 41.5 degrees C it seems reasonable to suggest that hyperthermia was the cause and the reasons why they might have developed heat stroke are listed in a separate response to you. And what were their blood sodium concentrations? This could also be compatible with the encephalopathy due to EAH. Also how many athletes have completed the Ironman Triathlon without this happening? Which is the more common occurrence - this condition or its absence? If there was no regulator trying to insure that this condition does not occur surely every Ironman triathlete would develop the condition. Thus the presence of such cases suggests the presence of a regulator, not its absence.

When it happens consistently regardless of the duration or intensity of training, then I have to conclude that the issue is dehydration. For instance, 2 hours riding in the sauna-like Florida summer heat with little water intake can easily cause me to lose 3% of bodyweight. Likewise running for 1-1.5 hours at 98F/85% humidity can do the same. Neither of these are even remotely close to my endurance limits, having ridden races of 200 miles and run several ultramarathons (and frequently run 6+ hours every weekend during ultra training). I don't disagree that it's a complex phenomenon, but on days of intense heat water loss seems to be the only consistent factor.

For instance, 3 weekends ago it was about 88F and moderate 50% humidity and I ran from about 10am to 4pm. I ran 7.5 mile loops in the forest (swamp) on sandy trails. At about mile 5 into the 3rd loop (~mile 20) I was really hurting and went from running a ~8:30 pace down to having to run/walk at an aggregate 10-11min pace. My running bottle was empty so I couldn't drink any more, and my sweat rate had dropped dramatically. I finally got back to the car and drank about 0.5L of water/Heed mix. Within a few minutes I was sweating again, my "perceived" temp dropped and I could go back to running again. After another 5 miles I started feeling even worse, and shuffle-walked the last 2 miles back to the car (miles 28-30). Based on a couple of studies mentioned in this thread, I would guess the following:

1) The combination of high temp and high humidity caused me to significantly dehydrate. Pre-run I was 162.2lb (about normal), post-run I was 156.8lb, a 3.3% drop. Without the extra 1lb of water I was about 4% down (danger zone for me).
2) The studies showed increased blood glucose and increased sweating immediately after a sugarwater mouth rinse and from drinking water. This is consistent with feeling better immediately after drinking about 1lb of water.
3) As I shed the extra lb of water over the next 30-40 minutes of running I went right back to the non-sweating, overheated, extremely low energy, can't run at all level.
4) The water was pretty hot from being in the car, so no conductive cooling was possible.
5) The weekend before I had run the same course with slightly lower temps (83-85F) and proactively drank 0.25-0.5L of water/Heed mix at the end of each 7.5 mile lap. I finished the last lap at 158.5lb and was overall nearly 30 minutes faster.

So what do I conclude from this? Drink enough water to maintain a maximum body weight loss of about 3lb. I can give plenty of other examples, with power meter files on the bike, etc. There's a definite point where I go from "fine" to "bonk" (200-220W versus struggling to push 175W) and it consistently happens at about 4-5lb weight loss. Not only that, it's a fairly rapid thing, usually within 5-10 minutes I'm fine and then bonking. If I stay within that "safe" range I can ride literally all day at 200W, so it's not a glycogen thing.

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Well, the sweat rate measurement was before/after excersize while drinking a known volume of water, so you would expect to see the exhaled water be a part of this. No doubt it does matter, even on cold days when you aren't sweating a lot in comparison...

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The CGM is best described in a series of 5 articles we wrote in the British Journal of Sports Medicine in 2004/5. There are a number of recent updates many of them published in the BJSM in the last few months. The model predicts that the brain regulates the exercise performance by determining the number of muscle fibers that are recruited in the exercising limbs. It does this to insure that exercise is always regulated to insure that the exercise bout terminates before there has been a catastrophic loss of homeostasis in any bodily system.

To my knowledge it is the only model that can explain why athletes begin exercise at different paces dependent on the duration that they expect to be exercising, and their ability to speed up in the last 10-15 % of most events (the end spurt) including interestingly the 42km marathon. If exercise were regulated by a progressive fatigue that develops in the exercising muscles (and is not influenced by the brain) then all exercise bouts would start at the same intensity and continue at that pace until fatigue began to appear causing a slowing of performance. The body would also not be able to increase the pace at the end of the exercise bout since it is not possible to reverse the (irreversible) muscle fatigue (failure) that had caused the slowing of pace up to that point.

You are welcome to read all our articles which present the other evidence that supports this model. Of course if the brain has no influence on performance, why do athletes ever worry about things like "mental preparation" and "mental coaching"?

If irreversible failure of the muscles is the main cause of fatigue then you cannot flog a dead horse, so to speak, by preparing your mind.

Our study currently in press showed that it is not possible for physicians at the end of the race accurately to assess the level of dehydration in athletes.

Sensitivity and specificity of clinical signs for assessment of dehydration in endurance athletes.
McGarvey J, Thompson J, Hanna C, Noakes TD, Stewart J, Speedy D.
Br J Sports Med. 2008 Nov 3. [Epub ahead of print]

If you don't measure the body weight before and after exercise you have no hope of determining how "dehydrated" is the athlete at the finish of the race using the usual clinical measures of "dehydration".

We no longer promote the use of the term heat illness. If the body temperature is not above 41.5 degrees C or the athlete clearly shows abnormal brain function (not due to EAH) then on what ground is a heat illness being diagnozed?

The condition normally called "heat illness" in athletes who collapse after exercise is usually exercise-associated postural hypotension which as I indicated in another post cannot be due to dehydration. Since the body temperature is not elevated in heat illness, then dehydration cannot be the cause of the appropriately elevated body temperatures in patients with "heat illness".

See: A modern classification of the exercise-related heat illnesses. Noakes TD.
J Sci Med Sport. 2008 Jan;11(1):33-9. Epub 2007 May 23.

Heat stress in sport--fact and fiction. Noakes TD.
J Sci Med Sport. 2008 Jan;11(1):3-5.

Thank you for confirming that medications need to be considered in all cases of heat stroke (see my previous post).

I would agree that the development of heat stroke is multifactorial. It is clear that not all these factors need be present and no one factor is on that list is always present. I would add that the "Some factor interfering with sympathetically-mediated sweating causing impaired sweating and hence impaired heat loss" could be severe dehydration.
I am not sure why you think that collapse after the finish line is evidence against dehydration. Clearly, athletes or others can increase sympathetic tone to maintain adequate cardiac output under stressful conditions and then when the stress is removed and "normal" feedback is returned the person collapses. This happens in war and in athletics.

I don't know that athletes with heat stroke collapse with "high" cardiac outputs. Cardiac failure could mean the inability to provide the demand, whatever the output. There is such a thing as "high output cardiac failure" you know. I mean I would expect them to be high as I would expect the body would be trying to cool itself but if the filling pressures are not high, it seems that the CO would not be as high as the body would like it to be. If the person is not sweating I think one can say the CO, whatever it is, needs to be higher. People with MH would have very high CO's (they are not dehydrated) but I am not so sure of other etiologies and what is meant by "high". Can you point me to a reference?

I am a little confused. You state athletes with heat stroke collapse with high cardiac outputs then you say that athletes who collapse do not have higher temperatures than those who don't. What kind of temperatures are you talking about?

Anyhow, I am glad to see that you have a low incidence of problems in your medical tent. But, we are trying to discuss what the issue is with those who do develop these disorders. Why do they occur and how can they be prevented? Your recommendations seem to work well for EAH. Not so sure for heat related illness.
Can you point me to a reference? Lots of things can result in "marathon collapse". I suspect dehydration is just one of them. It seems as if you are saying that the incidence of problems would go to zero if only the RD would not provide any fluids on the course. Aren't we trying to strike a balance here?
I will look forward to seeing that. I will state beforehand that not all cases of heat illness are related to hydration state. I look forward to seeing how you show that no cases could be related to hydration state.

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Frank,
An original Ironman and the Inventor of PowerCranks

The VO2max test is a brainless test since the experimenter not the athlete sets the work rate. Thus it can never be an appropriate test of the CGM. Please see the following:

Testing for maximum oxygen consumption has produced a brainless model of human exercise performance.
Noakes TD. Br J Sports Med. 2008 Jul;42(7):551-5. Epub 2008 Apr 18.

If you wish to prove or disprove the CGM you must study self-paced exercise. Which does not mean that there is not plenty of evidence that the brain limits the VO2max test. But if you don't study the function of the brain during the VO2max test, how would you ever be able to determine whether or not it is the regulator?

Let me get this straight. Are you saying that the brain modulates how hard we exercise (duh?) or that there is an inherent central mechanism that prevents one from exercising too hard, to the point of say, causing a heart attack or something? A governor prevents an engine from going above a certain speed. It does not prevent the engine from doing anything it wants below that certain speed. By self paced exercise are you referring to a 100 m pace or a 100 mile pace?

If one wants to test that there is a maximum limit to the engine then one needs to test that limit. As far as I know the best test of that is the VO2 max test, mindless as it is (if it required thinking it wouldn't be very reproducible). BTW, although the tester sets the work loads, the subject determines when the test is over.

So, could you state in a paragraph or two exactly what your CGM states?

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Frank,
An original Ironman and the Inventor of PowerCranks

Here is what I am getting from reading some of what you have written. Correct me if I am wrong.

You are stating that VO2 max is a brainless test because the effort is set by the tester and when people race the effort is set by the racer. Of course, if we define what the maximum effort the athlete can do is what the athlete actually does then I think we can all agree that there is a central governor. But, where we disagree is whether what the athlete actually does is all the athlete is capable of doing.

The only way to test what the maximum any athlete can do is to test them to exhaustion. The standard for doing that has been the VO2 max test. No one expects the athlete to actually compete at their VO2 max but people do use that value to compute how athletes should compete, especially in this day and age of power meters, when the athlete can actually measure what they are doing.

I don't understand your complaint with this test.

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Frank,
An original Ironman and the Inventor of PowerCranks

The reason I posted that link is you wrote: "There is no evidence that humans can run themselves into a catastrophic failure."

I submit that both those ladies ran themselves into catastrophic failure and that video is evidence of same. And, while you may think this is evidence to support your central regulator theory, it proves to me this central regulator, if it exists, is not very reliable, since it certainly failed in these two instances. That doesn't make it much of a regulator or governor does it. There are others. You might want to check out the name Julie Moss who had a similar failure in 1982 (see the video), well before the advent of EAH issues. Or multiple world champion Paula Newby-Frasier who had a similar failure about 1/2 mile from the finish in 1995.

I am not sure why you are choosing to ignore these obvious "catastrophic failures" that are, seemingly, the result of "simple" running. But, unless they are investigated and can be shown to not conflict with your theory I am afraid your theory has some serious holes. Some "governor"

While I don't know the medical findings associated with any of these incidents, I am sure you could find out if you were really interested as I suspect Ironman keeps those records. Maybe not. Or, perhaps you could contact the people involved. They might have access to the records of those incidents. Let us know what you find out.

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Frank,
An original Ironman and the Inventor of PowerCranks

I'm certainly not qualified to comment as my reading of the science is limited to one book about running, but a rather lengthy one (Ibid. your reference.)

While riding today, this thought occurred to me: why presume eating during exercise was not a selective evolutionary factor? Maybe a gene was evolved to create a hunger during running which would prompt hunters/runners/athletes to eat during exercise. While beneficial in the short term (e.g. during the hunt, during the race), perhaps longer term effects disfavored this trait. Thus, could it be that the reason we run or exercise only for two hours before bonking is that longer term exercise without rest is bad for us?

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It doesn't really matter what Phil is saying, the music of his voice is the appropriate soundtrack for a bicycle race. HTupolev

I don't think any other animals eat at a moderately high percentage of their aerobic capacity. Most are sitting around when eating. Perhaps because packaged nutrition is not available in the wild (aside from berries and bananas) :-) This alone is a good reason to stick to 10 k's, half marathons and olympic tri or less. I don't think doing longer events on a one off basis are bad for you, but I do think that day in day out long training (in excess of 2 hours per day) does take its toll over time.

Dev

I think it is pretty easy to explain why animals don't eat when hunting (exercising). It takes time and energy to digest and absorb food. During this time the energy requirement diverts from the energy available to the muscles. To account for this all animals store energy to be used during this period. As long as we stay under the limits that we can convert energy stores into high energy molecules used in metabolism we should be able to exercise continuously "forever", as long as we replace the lost water and electrolytes (for which there is no large storage repository).

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Frank,
An original Ironman and the Inventor of PowerCranks

Dr. Noakes,

Thanks very much fo taking the time to post here and answer so many questions.

I purchased Lore of Running 7 months ago and would rate it as probably one of the top 3 books I own. It is so informative and comprehensive. I have even brought it into my gastro-endocrinologists' office, for him to peruse in my diagnosis of Colitis last year.

I live and train in South East Asia and have done my very best to educate myself, regarding :dehydration / hyponaetremia / electrolytes.

Just recently, I completed a small duathlon 10km R / 40km B / 10km R. Although the temperature at commencement 07:30 was 29C with highish humidity, 2 hours later it was 35C and exceptionally humid ( apologies for the lack of humidity data ). The run course had absolutely no shade , there were no clouds at all and was run on black asphalt.

I considered myself to be as prehydrated as possible ,at commencement and had pre-loaded for 4 days prior , with 4000mg sodium phosphate / 2000mg glutamine in addition to +_ 3 Litres of diluted (Realemon Juice ) daily ,excluding training drinks.

My sweat rate is at least 2L per hour during this type of weather at this intensity and has been as high as 2.5L. Slightly lower during evening training ,at lower intensities +_1.5L per hour.

Throughout the event I hydrated , ( after the first 45 min segment ) , I drank 2.75 Litres comprising of :
- 1450 mg's sodium
- 4000 mg's sodium phosphate
- 400 mg's potassium ( and a banana on top of that )
- 50 mg's calcium
- 100 mg's magnesium sulphate
- 1150 mg's Vit C
- 2000 mcg Vit B2
- 2000 mg's glutamine.

In addition to this I consumed a 600 ml custom designed carbohydrate sports drink on the bike.

Considering that I feel that I raced the first 2 events of the race well within my personal capabilities , I found myself running out of breath running at a sedentary 5.30-6.00 min/km's!
I will add here that I run 3.35 marathon's , I have completed numerous 70.3's and 4 Ironman events.

I was 72kg's when I left home and 69.5 when I returned. 5'9".

Which brings me to the long drawn out question ( apologies )..... to what extreme does heat / humidity play in a "supposedly" hydrated athlete , racing within their respective ability and the corresponding increase in HR ?

I think I understand why the HR elevates , to facillitate cooling , but I am really unsure how to avoid this without slowing down.

Apologies for the drawn out nature of ths question , but I wanted to include as much detail as possible to facillitate your opinion.

Thank you in advance and again for posting here on ST.

Terry

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"You are never too old to set another goal or to dream a new dream" - Les Brown
"Discipline is the bridge between goals and accomplishment" - Jim Rohn

I think I understand why the HR elevates , to facillitate cooling , but I am relly unsure how to avoid this without slowing down. \\\[/url]

When someone figures out how to keep your HR down in extreme heat while still running at normal race pace for normal weather, then I can come out of retirement and take my rightful place among the Ironman greats..(-; You answered your own question just about as well as anyone else can. The hotter it gets, and the longer the race, the more you just have to slow down. To what degree depends on a lot of factors, the biggest is your own bodies paticular tolerance to heat, and how well you managed it during the race...There are lots of potential winners in Hawaii, but when filtered through this formula, there are very few...

Monty,

That was not the answer I was looking for :)

Funny that . I was discussing this with my wife ,whilst cooling in the pool that afternoon . I was telling her , that perhaps , I am just not genetically designed to perform well in heat. After all ,I am Canadian and it is very hot and humid.

I just figure that at some point my body would say to itself that "hey this idiot keeps exposing us to this extreme environment and intensity , perhaps we should adapt ?".
Well after 16 years here of which 8 has involved endurance training , perhaps it was too late of a start in this climate. Or I am just not genetically designed to perfor i this environment.

Coincidentally , I raced Kona some years back and did not find it hot at all. Additionally , I should add that I found the temperature and humidity VERY comfortable.

Thanks for your post:)

Terry

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"You are never too old to set another goal or to dream a new dream" - Les Brown
"Discipline is the bridge between goals and accomplishment" - Jim Rohn

I was telling her , that perhaps , I am just not genetically designed to perform well in heat. After all ,I am Canadian and it is very hot and humid\\

This may or may not be true in your case, but being Canadian has nothing to do with it. I have known folks that have never been exposed to heat, lived in cold climates all their life, and do great in the heat. And conversely, there are folks that are from hot enviorments, famalies have lived there for generations, and they suck in the heat. That is why I believe there are some factors that have not really been isolated yet that we have no control over. Other things we can tweek to some degree, but you can go only so far until you bump against those walls you were born with. Each person will find those walls once they do enough racing in hot enviorments, and like me, they will deny it for awhile, fight it tooth and nail, try every approach that someone can come up with, and in the end realise that fightning your nature is a losing battle..

On the other hand, I can kick serious butt in 40f degree weather, with wind, rain, or snow. I guess I was meant to be a real biathlete, not the bike/ run kind, oh well..

I do well at both ends of the spectrum.....35C and humid and minus 15C.

Where I fail miserably is 5-12C in the rain. I cannot keep my body working in wet cold. Dry cold is fine and heat and humidity is fine. I believe both these extemities requires the delivery of core heat to the extremities and skin surface, but low sweat rate (when you sweat profusely in really cold, you get wet and immediately freeze). In the case of minus 15 and cold, there is a layer of clothing that the heat then stays trapped under. But when it is 5-12C and raining, the heat delivered to the extremities is constantly sucked out of my body making me colder and colder and colder. I don't have a large enough layer of natural insulation (muscle mass and fat) to keep the heat trapped in my core which is somewhat required in wet.

I think to succeed in heat, you need to be lean, not hugely muscled, and have a very low sweat rate (In Kona 2006 for example, I only consumed 6 bottles of Gatorade during the entire bike and then whatever coke and gatorade during the run. Barely did 6L of liquid over a 10 hour race. This is somewhat the opposite of the well muscled, high sweat rate athlete that will succeed in wet cold (Monty is that you)?

Dev

Thans for that response , vry nformative.

I hav bumped into those walls quite a few times........I'm still trying to bust straight through them.

I will be racing IM Canada in August , which from what I recall , although hot , is substantially cooler than what I am used to. All things being equal , I usually do better in cooler climates ( Kona and IMWA).

I think I may join you in one of those cooler 40f races and see if I excel there too :)

Thanks again !

Terry

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"You are never too old to set another goal or to dream a new dream" - Les Brown
"Discipline is the bridge between goals and accomplishment" - Jim Rohn

This is somewhat the opposite of the well muscled, high sweat rate athlete that will succeed in wet cold (Monty is that you)? //

I dont know if I'm well muscled, but 5'10" 160lbs was my usual racing weight. I think size is a factor, but not a limiting one. Lot of guys that were well over 6ft, and 175lbs+ have done well in Hawaii. Dave Scott was quite well muscled, and not a little guy. When I watch the top 20 guys over the past few years, there are a lot of big guys mixed in there with the smaller ones. I have no excuse in size area, probably most of the ironman top 10 since its inception were guys my size and bigger. The Greg Welch body size was the exception, not the rule...It is mostly about heat tolerance, regardless of your size. I expect that Matt Reed and Lifetime champion(name escapes me right now) will do very well in Hawaii, and they are huge by triathlete standards....

I am not sure it is possible to know from the data you provided whether you were over hydrated or dehydrated. Both could have affected your ability. The one quesition I am sure Dr. Noakes would be asking is what was your weight at the end compared to the beginning?

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Frank,
An original Ironman and the Inventor of PowerCranks

That is a great point Frank , thanks for the reminder on that :)

I was 72kg's when I left home and 69.5 when I returned.5'9"for what it's worth !

I will insert in my original post.

Thanks again !

Terry

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"You are never too old to set another goal or to dream a new dream" - Les Brown
"Discipline is the bridge between goals and accomplishment" - Jim Rohn