Welcome to the Science of Sport, where we bring you the second, third, and fourth level of analysis you will not find anywhere else.

Be it doping in sport, hot topics like Caster Semenya or Oscar Pistorius, or the dehydration myth, we try to translate the science behind sports and sports performance.

Consider a donation if you like what you see here!

Did you know?
We published The Runner's Body in May 2009. With an average 4.4/5 stars on Amazon.com, it has been receiving positive reviews from runners and non-runners alike.

Available for the Kindle and also in the traditional paper back. It will make a great gift for the runners you know, and helps support our work here on The Science of Sport.

Wednesday, October 17, 2007

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 staggeringan 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 10th 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!


Arno said...

Hi there, please consider cross posting to http://sportblog.co.za

I want to launch with a Featured Blogger on the home page, and would be happy for that to be you

Ross Tucker and Jonathan Dugas said...

Hi Arno,

Thanks for your message about Sport Blog.

Why don't you contact us at sportsscientists@gmail.com and we can discuss this further?


Kind Regards,

Jimson Lee said...

I have to check my sources here.

Back in 1976, and maybe later marathons, water stations during an Olympic marathon were restricted at the 5, 10, 15, & 20 mile stations only. That's not a lot of water on a hot day!

Of course, the fans along the route were permitted to sprinkle the runners with hoses, or even provide a free drink.

In the 1977 Boston marathon, winner Jerome Drayton complained about the lack of water stations on the course.

Ross Tucker and Jonathan Dugas said...

Hi Jimson, and thanks for your comment!

The IAAF rules governing fluid ingestion during races saw progressive change over the past 60+ years.

Currently I think it is every 3km that a race can provide fluid and/or food. That was 1990, and it might be even more frequently now.

The important thing about this is that athletes should have access to the fluids, but not because they need to drink to stave off dehydration. Instead, the high frequency allows them to drink to thirst when they want it.

However in mass participation races, there seems to be a direct relationship between the number of aid stations and the number of cases of hyponatremia, suggesting that people will ingest too much fluid when given such access.

Thanks for visting!

Kind Regards,

Anonymous said...

What are you views on electrolyte replacement? A lot of attention seems to be paid to drinking a lot of water, but most people I know use something like Infinit, salt tabs, or even Gatorade Endurance to replace electrolytes/sodium on long workouts. I've read that some marathons provide salt packets to runners during really hot races. Sorry if you've already written about this and I missed it. I know that if I drink only water during tough workouts, I'll generally get a massive headache afterwards, but if I drink something with electrolytes/sodium, I don't.

Ross Tucker and Jonathan Dugas said...

In response to Anonymous on 2 November:

Electrolyte replacement, especially sodium, does not appear to be necessary during endurance exercise. We say this because currently there is no evidence to suggest that ingesting sodium during endurance exercise enhances any of the desirable outcomes---performance, cramps, fatigue, etc.

The way the physiology works is that the concentration of sodium is the regulated variable, and not the total amount of it in your body. Therefore if the plasma volume decreases slightly, then the concentration rises, even if you are losing some sodium.

In addition, first the body attempts to replace any lost volume, and only then, once volume has been restored, does one's sodium appetite kick in to correct for any sodium losses.

If the "tough" workouts you mention are of long duration, I suspect the headaches can be attributed to a lack of carbohydrate ingestion. If the workouts are short but just hard, then it is unlikely that either is fluid or sodium loss is causing the headaches since the loss are so small during short workouts.

I hope that helps! Thanks for visiting the Science of Sport, and we hope you keep on coming back.

Kind Regards,

Louise said...

Dear guys,

So here is a practical problem involved with only drinking to your thirst during exercise. In many sports, access to fluid is restricted - to aid stations, half-time, soigneurs etc etc. The reality is that athletes may not be thirsty the first times they are presented with an opportunity to drink. However, by the next opportunities, there are now very thirsty. The problem is exacerbated for elite athletes who sweat at high rates during high intensity exercise - because they are unable to drink at a rate (either because of GI issues or the time taken to obtain a drink) that keeps pace with true sweat losses or maintains osmolality (or whatever you want to measure). So once they are above the thirst threshold, they are unable to regain the lost territory. Being unable to quench your thirst during your sporting activity can be uncomfortable and distracting. And this pattern of "relying on your thirst" can lead to unnecessarily high fluid deficits. Why are you so opposed to athletes developing a personalised fluid plan based on likely sweat losses, and the likely opportunities to drink during the sporting activity AS WELL AS THIRST. Banging on about only drinking if you are thirsty seems as dogmatic as the dogma it aims to replace. As for the argument about cats and dogs and drinking bowls.....These animals are not playing by rules that require them to stay on a soccer pitch at 35 degrees until a 45 min half is over, or run/ride in Beijing events with aid stations paced out. What is wrong with these athletes having a drink at the first aid station or the first injury break when they can ge to the edge of the pitch, even if they aren't totally thirsty, so that they can better pace out their fluid intake over the often random or restricted points of access to fluid over their event?

Ross Tucker and Jonathan Dugas said...

HI Louise

Thanks for the comments, you have good points that "IF" the athlete faces potential fluid restrictions, then a pre-planned strategy must be adopted. But this scenario is so vastly different from what is actually experienced during mass participation events that it bears little resemblance and can't be compard.

The point we emphasize about drinking to thirst is made because the alternative is killing people. Pure and simple. I suspect that you are in Australia, or somewhere outside the USA, where the problem of death relating to hyponatremia is not as serious as it is in other parts of the world, and I don't know what kind of races you are referring to when you talk about the possibility that an athlete can not be thirsty at one aid station, but be very thirsty (too the extent that it's "too late" as you put it) at the next - let's not forget that the aid stations are probably with 1.5 to 2km of one another in most of these big races.

And so unless the athlete is running in 40 degree heat, these 10 minutes are not going to be critical.

HOWEVER, they do become critical when the athlete is drinking too much. Because what happens, and this is documented in the literature, is that an athlete will obey the mantra "I must take a drink at every aid station" to prevent thirst.

Consider then a 60 kg women, doing a 5 hour marathon, where aid stations are placed every 2 km (which is rather sparse by comparison with some races). THis women, assuming she has a cup (250ml) is going to drink a total of 21 cups, and 4L of fluid during the race, MINIMUM. Now, given that she's running the race in 5 hours, her sweat rate is highly unlikely to be higher than about 500ml/hour, which means she will have gained between 2 and 3 L of fluid by the finish line.

That is of course a situation that can be, and often has been fatal.

So here's the differences between your question and the real situation - fluid access is NEVER restricted in the big city marathons and organized events, where most of these deaths occur.

I dare say, if you did a little experiement, you'll find a positive correlation between the number of deaths during marathon running and the number of aid tables on the route, and the level of organization of the race. It simply does not happen that your 5 hour marathon runner is ever faced with water restrictions, unless he's running in the Marathon des Sables...!

So leading on from that, the elite runners, or any other runners, will never be "very thirsty" unless they choose to miss a drinking station for tactical reasons - this is often done, as I'm sure you are aware. Yet amazingly, they persist in doing it? Perhaps someone should tell them it's harmful to do that? Or perhaps they already know their body can handle it because a nother water station is just around the corner, a kilometer or two later.

Or even better, perhaps the elite atheltes have figured it out, and as Gert Thys (2:06 marathon) once said, 400ml during a marathon is about the limit. The elite guys wet their mouths, they take tiny sips and lose massive body weight when they run. They don't defend weight, and I dare say they are quite 'liberal' in the defence of osmolality, because they know that it can be restored after the finish. Again, what constitutes normal at rest is not the same as during exercise.

Now, the other point you asked is why we "are against athletes developing a personalized plan based on sweat losses". We have adopted that position because determining sweat rate precisely is IMPOSSIBLE during an event. I'm not sure if you are active, but you should try to estimate your sweat losses on different days and across seasons, during races and different paces, and work out just how much variation there will be as a result of weather and pace changes, in particular.

For example, you religiously weigh yourself before and after every run, and work out that your typical sweat rate is 700ml/hour. But in your first marathon, it's a few degrees cooler than usual, your pace is a little slower than for all those 8 or 10km training jogs and so now suddenly, your sweat rate is 500ml/hour. Big deal? Well, not if your race is going to take you 5 hours, and you're out by 200ml/hour, because you'll have gained 1L of water by the finish. That is often enough to cause a lethal drop in sodium levels. We had a case in teh Argus cycletour who had exactly this problem - she worked it all out, did what was planned and ended up in hospital.

No one I am aware of has ever landed up in hospital as a result of drinking to thirst.

So while it may seem dogmatic, it's actually just saying "let it go", the body knows and you'll be fine, just as you were before the sports drink industry came along and told the whole world our bodies were too stupid to know when to drink.

Ross Tucker and Jonathan Dugas said...

Just a quick addendum to my previous post - a little typo in the example I gave:

If a 60kg woman drink a cup (250ml) at a station every 2km, she would of course consume 5L during the marathon not the 4L I typed. Her resultant weight gain, given a normal sweat rate, would be around 2.5 to 3.5L.

And then one other thing - on a football field, when an athlete jogs over to the sideline to grab a drink of water, you use that as an analogy of how a 'pre-planned' strategy will delay thirst. My argument is that the reason that player is coming there to begin with is because he feels thirst to begin with! Why do we not see all 11 players rushing to the sideline? They're all influenced by thirst, not a scripted routine drawn up by the coach prior to the game, surely? If this is done, then I think it's bizarre. Because in a team sport such as hockey or soccer, with so many stoppages, all it takes is a short time out, a jog to the touchline and squeeze of a water bottle. And players do this all the time. I'll bet that there are some players who do it four or five times in a half, others maybe once, maybe never. POint is, it seems to me they are listening to their bodies.


garydempster said...

interesting that you cite Tom Simpson as an "anti-drink" advocate, as he rather famously collapsed and died on the side of the road during a hot TDF stage... perhaps if he'd had access to Gatorade, he'd still be with us today?!

i thought it had become well-established by now that hyponatremia was caused by drinking excess water "alone", without sodium, and that simply taking some sodium stops or greatly reduces it from occurring?

Ross Tucker and Jonathan Dugas said...

Hi Gary

Tom Simpson was also a known amphetamine user, and that was responsible for his death. I don't believe any amount of fluid would have helped. People have died in temperatures of 4 degrees celsius as a result of heat stroke, so the fluid is actually pretty minor.

As for the hyponatremia cause, it's not well established that taking salt prevents it. In fact, what we tried to do later in this series - Part 3 or 4, I think - is look at sodium supplementation to show that drinking sports drinks does very little to prevent the fall in sodium. So drinking too much Gatorade is just as deadly as water - there have been deaths and many medical complications as a result of drinking too much Gatorade.

Free Themes said...

Dear Jonathan & Ross,

May I offer you a free customized header graphic related Science of Sport blog.

Please let me know if you are interested or check the sample gallery at: http://www.freewordpress.org

Thanks !

Issues in Sport said...

So once they are above the thirst threshold, they are unable to regain the lost territory. Being unable to quench your thirst during your sporting activity can be uncomfortable and distracting. And this pattern of "relying on your thirst" can lead to unnecessarily high fluid deficits.