Part I: History of fluid intake and a conflict of interest

Today we begin our five part series on fluid intake during exercise. As discussed, we will look at this complex and somewhat controversial issue over the next two weeks, covering the following topics:

The story begins, as most do, at the beginning…a look at the history of fluid intake and drinking during endurance exercise, which serves to illustrate an important point, one which will be covered again and again in this series…For this post, we acknowledge Professor Tim Noakes of UCT, the fluid pioneer whose lifelong pursuit of the truth in this area (and a lone battle for much of it) has thrown up the excellent quotes and anecdotes we use as we delve into the issue.

Don’t drink – it’s harmful?

Had you been around to run in the 1908 Olympic Games in Rome, you would be reading this with a sense of bewilderment at how things have changed. Today, runners are told to drink, drink, drink. Drink to replace ALL weight loss. Don’t get dehydrated, and so on. But your recollection of running in the early 1900’s would have been that you should NOT drink during exercise! Remarkably, 100 years ago, runners were being told by “experts” (that is, commentators on the sport and fellow runners) that drinking would be detrimental! For example, this quote, by James Sullivan in 1909:

“Don’t get in the habit of drinking and eating in a marathon race; some prominent runners do, but it is not beneficial”

This was not isolated advice. Joe Forshaw, who won the silver medal at the 1908 Olympic Games marathon once said “I do not believe in eating during the race, as it can scarcely benefit one, as no nourishment can come from the food till digested, and the race will be finished before the food would be digested.”

And then Jim Peters, to many the greatest marathon runner in history, once said that “… (In the marathon race) there is no need to take any solid food at all and every effort should be made to do without liquid, as the moment food or drink is taken, … some discomfort will almost invariably be felt.”

Runners were not alone in this attitude – Tom Simpson, cycling world champion and Tour de France contender in the 1960’s, pointed out that in his time “Four small bottles for a long stage [of the Tour], it is frowned upon to drink more…“Avoid drinking when racing, especially in hot weather. Drink as little as possible, and with the liquid not too cold. It is only a question of will power. When you drink too much you will perspire, and you will lose your strength.”

And then finally, the winner of the “camel” award for endurance exercise without drinking is Jackie Meckler, who won the 89 km long Comrades Marathon five times. The race took him just under 6 hours, and his approach to fluid intake? “To run a complete marathon without any fluid replacement was regarded as the ultimate aim of most runners, and a test of their fitness”

A change in perception – the ‘new’ approach

As I’m sure any reader will appreciate, this attitude – drink infrequently, never if possible – is radically different from the current advice. For around the 1970’s and 1980’s, the winds of change were blowing through endurance exercise and fluid replacement. We shall look at the research that drove the paradigm shift in our next post of this series, but suffice it to say that the advent of the sports drink industry, and the money that accompanied it directed a new approach to fluid replacement of runners.

And so by the 1990’s, studies were being done that showed that dehydration was the biggest possible threat to the exercising athlete. These studies are a point of contention and will be evaluated in future posts, but the net result of the research they threw up, was that the advice to runners changed dramatically. For where previously, runners were challenged to finish a marathon without drinking, the new advice (in 1996, in this case) included:

“The greatest threat to health and well-being during prolonged exercise, especially when performed in the heat, is dehydration…If this accumulation of heat is not dissipated, it will lead to hyperthermia and the potential to suffer a fatal heat stroke”.

And so in 1996, the American College of Sports Medicine, the accepted leading authority in the field, issued a position statement on fluid replacement during exercise, which stated that:

“Runners should be encouraged to replace their sweat losses or consume 150-300ml every 15 minutes (600-1200ml per hour)”.

There are a few relevant points about this position stand. First, it’s a world apart from the historical practice, because it now suggests that any loss of fluid could be harmful to performance and to the athlete. Secondly, it makes a blanket recommendation of the rang of fluid volumes that would be required, without any acknowledgement of the fact that the exercise intensity AND the environment are critically influential to fluid losses (and thus requirements, according to the paradigm).

This is very much the scientific equivalent of hedging one’s bets, and as we’ll see, the ACSM position stand later evolved into a more ‘scientific’ approach, when runners were told they should weigh themselves before and after a run to know how much weight they had lost. This of course, presents the runner with a significant dilemma – how do you know your sweat rate, or your body weight change during running? This is impossible, unless you run with a bathroom scale in your pocket! And making this measurement after training runs is not guaranteed to be accurate either, unless you can guarantee the same environmental conditions and running speed, which you can’t. So the position stand put athletes in a tricky position to begin with. The “compromise” at this stage (mid-1990's) was even worse – it initially suggested to drink as much as possible.

Blurring the lines – marketing or science?

It was at this stage that the lines between “scientific advice” and promotional strategy had blurred. It is important to note that much of the research on the topic was funded by Gatorade, a company that produces sports drinks. The conflict of interests this created is staggering – an entire Institute, called the Gatorade Sports Science Institute, was created. A website, with a section dedicated to educating the public on fluid replacement needs, is sponsored by the company aiming to meet those needs. And perhaps not surprisingly, all the research of this time pointed in one direction – you need to drink, drink and drink. And when the marketing arm of the company used this information, they encouraged you to drink Gatorade!

It is easy then, to make the assumption that the research and the marketing strategy were one and the same, because advertorials (think adverts, but with authority, because scientists endorse them) were being issued telling runners to drink as much as they could.

Scientists suddenly find themselves in the role of endorsers

So much as you will see Grant Hill drinking Sprite and Tiger Woods wearing Nike, scientists were “paid” to give the product a push. For example, one advertorial issued runners with the “Ten Commandments” (of course, this title meant they MUST be true!). The very first commandment was to

“DRINK BIG. Drink, drink and drink some more. Not just on race day but every day. Dehydration is one of the most common causes of premature fatigue during training and competition and it’s also one of the most common causes of sports injuries – pulled muscles cramps, dizziness, nausea and heat exhaustion.”

So important was drinking that runners were encouraged to practice it, just as they would train for the race. This was the 10^th commandment:

“Like training for your big race, you need to train yourself to drink lots of fluids before, during and after the race. Remember, practice makes perfect!”

The likes of Jackie Meckler and Jim Peters would never have seen anything like this before.

The problem – overdrinking can kill

This approach soon produced results – an undesirable kind. For it is without doubt possible to drink too much (a fact even acknowledged by Gatorade in subsequent position stands). And that is exactly what happened. Spurred on by “scientific studies proving” that your body needed 1200ml per hour (see picture to the right), runners of all shapes, sizes and speeds were set on drinking – the all followed the First Commandment – Drink, drink, and drink some more.

The problem, as we shall see in post 3 of this series, is that the excessive intake of fluid can cause the plasma be diluted to such an extent that a condition known as hyponatremia develops. And people die as a result of hyponatremia. The condition was first called water intoxication, and the first reported case came in 1981, at the Comrades Marathon. A paper was written, and published, by Professor Tim Noakes, titled Water intoxication: a possible complication during endurance exercise.

Remarkably, in the 20 years since that event, the scientific fluid-intake community, headed by the Gatorade Sports Science Institute, ignored this possibility and continued to advocate drinking to replace all sweat losses, encouraging runners to “drink everything in sight”. They even published papers suggesting that hyponatremia was caused by DEHYDRATION and not excessive fluid intake! The result of this “promotional” campaign, camouflaged as science, was that 247 cases of hyponatremia were reported between 1985 and 2002. Seven were fatal.

The compromise – updated fluid guidelines of 2007

A compromise of sorts was eventually reached, and the most recent (2007) ACSM position stand on fluid replacement reflects the growing awareness of the dangers of overdrinking. Gone was “the drink as much as tolerable” statement, replaced by the recommendation that one should drink during exercise "to prevent excessive (>2%) dehydration". In other words, it’s now recognized that if you drink more than you sweat, you’re running into trouble. And 2% dehydration is now defined as an upper limit - 1 to 2% is thus acceptable, which is a significant departure from the previous concepts. The problem is still the dogmatic paradigm with which dehydration is approached - the entire basis is that dehydration is bad, despite a lack of evidence for this attitude.

For example, it's stated that dehydration is a major factor responsible for the development of heat stroke. Yet when the heat stroke cases are analysed, only 16% actually have "dehydration", however that is measured (this is a problem, as we'll see). So quite how a condition can be caused by something when only 1 in 6 cases have it is very odd, and one can only conclude that there is some other incentive to link dehydration to heat stroke. But the evidence is harldy overwhelming - 1 in 6 people. And that's not to mention the thousands who are "dehydrated" and not overheated! As we'll see, MOST people finish events having lost between 1 and 4% of their body weight. Yet fewer than 0.5% of people ever overheat. There's something very wrong with that picture.

And then finally, the biggest problem is that they are still prescribing the replacement of ALL sweat losses. The practical limit to this, in that the runner cannot possibly know their sweat rate, is the biggest barrier. And that leaves us in our current situation – runners believe that they HAVE to drink to replace sweat loss. They believe, having been told this for many years, that if they are even slightly dehydrated, that they’re in trouble. They also believe that thirst is not a good enough guide – if you’re thirsty, it’s too late.

When science becomes marketing - loss of integrity and fatal consequences

But is this true? We’re working towards an answer for that in future posts. But in this post, we’ve just highlighted the evolution of our fluid beliefs. We hope it strikes you as remarkable that things have changed so much since the 1960’s and before, and what an extra-ordinary conflict of interest exists around the issue. And we hope that it’s given food (or drink, as the case may be!) for thought, for in our next post, later this week, we’ll tackle the issue of dehydration and temperature.

Those scientific arguments on this particular issue have long been debated. But what we would like to do is emphasize the “marketing” debate, because what we have here is a gross conflict of interests, which has been disguised as good and pure science that has resulted in the death of runners as a result of the excessive fluid they have ingested based on that science.

The perception may thus be that Gatorade funds research. It does NOT – rather, it funds the endorsement, the “image rights” of scientists who proclaim the dangers of dehydration when the evidence accumulates all around them. In this way, science becomes marketing. In our next post, we'll begin an evaluation of that evidence.

Join us then!

Fluid intake, dehydration and exercise: A new series of posts

First let us say a big "Thank You" to everyone who has asked questions, posted comments, and contributed to the debates here at the Science of Sport. We have had an incredibly positive reaction to our posts on the Chicago Marathon, and many relevant and good questions were asked in the wake of those posts. Therefore we are excited to bring you a new five-part series of posts on fluid replacement during exercise.

In this series we will examine the following concepts and ideas:

1. The history of fluid replacement in the marathon and endurance sports
2. Does dehydration really cause you to have a higher core temperature?
3. Evaluation of laboratory-based studies vs. field exercise: Is there a difference?
   
4. Hyponatremia: a disorder of fluid, not sodium, balance
5. The physiology of thirst: Why waiting until you are thirsty is NOT too late

We sincerely hope that this series generates as much interest as our previous two series on running technique and men vs. women in running. This debate is controversial, and has stirred serious debate in the past, as I'm sure it will now. We welcome this of course...

But at the heart of this debate is an eternal conflict between science and the commercial world. As we will see, the lines between marketing strategy and research strategy become blurred and confused, scientists begin to drive product sales through 'endorsements' from research, and a conflict of interests is created that cannot be tenable. The topic is worth discussing for this reason alone, but also affects every single person's training routine.

So tune in tomorrow for Part I, and keep on coming back for the full story. Again, because it's a series (in order to avoid writing a thesis in one go!), we'll move systematically through the topics, and so may seemingly omit points from intial posts. As always, we will rely on you, the reader, to ask the unasked questions, and to contribute to the debate with your insightful comments. We'll certainly do our best to bring a scientific analysis and explanation of these everyday concepts, and hope we can help you understand them better.

See you then!

The uniqueness of exercise: When "abnormal" is normal

Over the last week, we've been running two simultaneous threads here on The Science of Sport. There's our Women vs. Men in running series, which has looked at the differences in performance between the genders and whether women will ever beat men in running events (there's one more part to come in that series, I haven't forgotten!). Then the second has been our post-Chicago Marathon analysis. In case you haven't heard yet, the Chicago Marathon last Sunday was heavily affected by high temperatures - the hottest race in the 30 year history of the event.

And we've been discussing the merits of the arguments put forward in the media after the race. Quite frankly, there has been some highly irresponsible reporting, ranging from premature assumptions around the sad death of Chad Schieber to aggressive attacks on race organizers for failing to provide water, and even for failing to cancel the race at the start. We're not particularly concerned with picking apart these arguments now, that's been partly done in recent posts. And we'll discuss it further in future posts.

But this post is about an interesting observation we've made regarding how people respond to these kinds of "physiological failures". Because what tends to happen is that people look at exercise and something like heat stroke and apply regular, text-book physiology to attempt to interpret the situation. But unfortunately, exercise is a little more complex than that...

A snap-shot from exercise - a worrying picture?

Let's take a hypothetical runner, call her Camille, aged 32. You take a physiological snapshot of Camille during the middle of an easy three hour training run. You see the following:

• Heart rate = 160bpm
• Breathing rate = 32 breaths/minute
• Minute ventilation = 15L/min
• Cardiac output = 16L/min

One can easily recognize that all these measurements are massively elevated compared to "normal". In fact, if you showed a doctor just these stats, he'd make a diagnosis that this person is hyperventilating, has a dangerously elevated heart rate and that their cardiorespiratory measurements indicate someone in severe distress. This person is likely to be admitted to ICU for observations.

But hopefully, once you tell the MD that Camille was running at 6min/km, he'd recognize that these very abnormal measurments are in fact quite normal.

The plot thickens - adding to the complexity

That's the easy part. Now let's look at a few more measurements from our "snapshot":

• Body temperature = 38.9 degrees Celsius (102F)
• Sweat rate = 1.5L/hour
• Skin temperature = 29 degrees Celsius

Again, everything is elevated. The doctor is likely to see this body temperature, the fact that Camille is sweating profusely and has a high skin temperature and suggest that perhaps Camille needs a day or two of bedrest. If you are reading this at your desk and your body temperature is 38.9C, then most certainly, you would know all about it! You'd feel shivers and cold, even though you're burning up, because you'd likely have a fever.

But Camille doesn't even notice this - she feels comfortable and wouldn't know that on any other occasion, she'd be diagnosed as very ill. Again, however, MOST doctors and 'experts' will recognize that because Camille is exercising, these values are actually normal! They contradict everything you've read about "normal" in a textbook, but that's fine, because exercise changes "normal". So we make a concession that sometimes, a physiological measurement that appears dangerous is in fact quite safe. So then, why do we not have the same attitude towards the next batch of measurements....?

The acid-test: Is this measurement "abnormal"?

So Camille finishes her run and jumps on a scale.

• Her body weight = 62 kg. Her normal body weight, by the way, is 64 kg.

Now suddenly, we have panic stations! Camille has lost 2kg! That equates to about 3% of her body weight. We immediately jump to the conclusion that she must be dehydrated! How could this happen? She had access to some water while she was running, so why didn't she drink enough to replace this? The run took her 3 hours and so assuming her sweat rate was 1.5L/hour, she sweated 4.5 L during her run! But for some reason, she only drank 2.5 L, and lost weight. "Did she not know that this would impair performance and put her at risk of overheating?" is the cry of people who hold to the theory that dehydration is dangerous during exercise.

"What might have possessed Camille to drink less than she should have? Does she not realise how dangerous dehydration is?" they say. After all, even 2% dehydration impairs performance by 20%. Or that's what the scientists from the Gatorade Sports Science Institute say!

The danger of making physiological interpretations out of context

Hang on a moment here - the first two sets of measurements showed us that when we exercise, what is "normal" is different during exercise. Yet the second we start to talk about dehydration and body weight, suddenly, there's no concession made for the possibility that perhaps during exercise, a slight body weight change is normal...Think about that for a while - we allow heart rate to rise, no problem. Cardiac output, breathing rate - no problem. Body temperature that normally suggests fever - no need to worry. But as soon as body weight is different, that's a crisis!

And the reason this perception exists is because we have been told that this is the case, by a body of research that may be sound in principle, but fails to acknowledge that during exercise, the body is quite content with change...it allows the physiology to change substantially - the cardiovascular system, the blood pressure, the body temperature, everything is so tightly regulated, yet during exercise they all change. No one has ever suggested that we should aim to keep our body temperature down to 37 when we train!

Yet for some reason, we've been told that a fall in body weight is dangerous and detrimental. There are a number of studies that have 'proved' this, but they are all fraught with potential problems. These problems are not technical and nor are they related to the study design - they are good scientific studies. But they are done in laboratories, and their relevance to what really happens during exercise is so limited. They have funded much of the research of those scientists who perform the studies. Given the funding source, one can hardly be surprised that they conclude that drinking more is beneficial.

But effectively, what these scientists have done is make the same mistake a doctor would be making if he diagnosed Camille as having a fever based on her high body temperature!

Introducing a debate around the issues

So there simply is no basis for the commonly-held belief that "any level of dehydration impairs performance". The most basic evaluation of this claim is the FACT that elite marathon runners, who win the races, are THE MOST DEHYDRATED. Elite athletes almost always lose 2 or more kilograms in a marathon. Now, the claim that has been made is that "2% body weight causes a 10% impairment in performance" (this is a true claim I heard at a scientific conference once. The actual figure varies, but it's always between 5 and 20%!). So let's say you're Haile Gebrselassie - you've just run 2:04:26. But you were 2% "dehydrated" when you finished. So that means if you'd just drunk more water you'd have run 1:53:07! Anyone else think something is wrong with this picture?

But then what happens is we say "the elite are different", everyone else has to prevent dehydration. Yet for that claim, there is no proof. No proof that people who lose fluid fail to sweat enough, no proof that dehydration leads to heat stroke, no proof that it impairs performance IN FIELD EXERCISE. There's proof in the lab, allright, provided you don't use a fan. Then it seems to make a difference. But not for out of doors exercise.

Over the course of the next few weeks, we'll delve a little deeper into these concepts and look at the whole dehydration and fluid intake issue. I realise that there is a substantial part of the argument missing from THIS POST, but this is just the philosophical starting point to the discussion, which we'll go into it step by step over the coming weeks.

Join us then!
Ross

Read our post-race report from Chicago and our explanation for the high number of collapsed runners here

Post-Chicago analysis continued: One patient's details

The news media are slowing down a bit here in Chicago, but the questions still remain---and we are not talking about why the race ran out of water, if they even ran out of water, or why they shortened the course. Rather, we are most interested in the runners who remained in the hospital on Monday evening. News outlets stated on Monday that 10 remained in the hospital, although no details were ever divulged about the diagnoses of these runners, which raises questions about the reasons they were admitted overnight.

Heat stroke - diagnosis?

First, if indeed the diagnosis is heat stroke then the first thing that must be done to confirm this diagnosis is a rectal temperature. As we have stated here previously, this is a crucial measurement that must be made for this differential diagnosis. Without it, you simply cannot confirm if the person has heat stroke or postural hypotension or something else. If the individual does indeed have a rectal temperature at or above 42 C (107.6 F), then active cooling in the form of ice-water immersion must take place, and even when it does it is possible that some tissue damage might have occurred and the person might require further monitoring.

However the signs and symptoms of "dehydration" and another condition, hyponatremia, are similar, and one can and often has been mistaken for the other. These include nausea, vomiting, and headache, among others. Hyponatremia is worthy of a post on its own, and we promise we will do one very soon. In short, it is caused by ingesting too much fluid, which causes the concentration of sodium in the blood to fall. Therefore it is a problem of fluid balance in which there is too much fluid, and not a problem of sodium balance as many people argue.

So whether or not the runners who remained in hospital were being treated due to heat stroke or hyponatremia is to us a crucial question, primarily because the race has been railed for not supplying enough water, which many people think is the cause of the hopsitalizations. We were fortunate to have access to the admission details of one of the hospitalized runners, and it is telling.

One case from Chicago

This runner began feeling bad at 20 miles, but did finish the race. They had a fainting episode sometime after the finish, the importantance of which is that this runner collapsed after they had stopped running. The athlete was admitted approximately one hour after the finish with the following results (normal values in brackets):

• Serum sodium concentration - 130 (135-145)
• Troponin - 0.11 (less than 0.1)
• Creatine Kinase or CK - 4102 (35-232)
• CK MB - 82.9 (5.1)
• Rectal temperature - 37.1 C

First, a quick explanation. . .

Tropinin:
This is a substance used to help confirm the diagnosis of a heart attack, which means this runner suffered a heart attack? Not quite. Prolonged endurance exercise can elevate the levels of this substance in the absence of any cardiac abnormalities.

CK and CKMB:
In the clinical setting, also a measure of cardiac damage. However, in exercise physiology we use this enzyme as a marker of muscle damage. CK, for example, is an enzyme found in the muscle , and the only way it gets into the blood is if the muscle is damaged. As you will know, this happens during marathon running. Many scientists are interested in muscle damage and repair, and this is an objective method to quantify the degree of muscle damage. Plenty of scientific evidence exists showing that after marathon running CK levels are vastly elevated.

Rectal temperature:
Ummm. . .ok, we all know what this one is! But seriously, the normal exercising range for the rectal temperature is 37-41+ C. Most people do not reach 40+ C, but in trained athletes rectal temperatures above 41 C have been documented, and more importantly they have been measured in the absence of any signs and or symptoms of "heat illness" or heat stroke. But in any case, this runner's rectal temperature approximately one hour after the marathon was totally normal, and in fact it was at a resting value.

Serum sodium concentration:
This measure reflects how diluted or concentrated the blood is. Most people finish marathons (and longer races) within the normal range, and furthermore the normal response is to maintain or even increase slightly. It is not normal for this value to fall during exercise. When an athlete presents with such a low sodium concentration it is a clear indication that they have ingested too much fluid. The tricky part is that "too much" is a relative amount and does not necessarily mean gallons and gallons----although fluid ingestion on that scale has been documented during endurance exercise.

The problem is that sometimes the body inappropriately secretes a hormone that promotes water retention. When you ingest too much fluid, this hormone quietly goes away until you need it. . .however, some of the stresses that occur during exercise can perhaps trigger its release, and that is why some athletes present with hyponatremia even when they ingest apparently modest volumes of fluid during their race.

Granted that is an entirely simplified explanation of hyponatremia, and we will follow with a full series of this condition and why and how it came about. However the take home message here is that this runner, and we suspect more than a few others, remained in the hospital on Monday not because of a heat-related problem, but because of a fluid-related problem---namely, hyponatremia---and this fluid problem was not a lack of fluid but rather a gross excess of fluid.

So be sure to come back later for the follow up posts on this and other runners as we obtain information, or even better, subscribe to The Science of Sport and get the posts delivered directly to your inbox.

Thanks for reading!

Read more insight from the Chicago Marathon in our post on heat stroke and running HERE