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Tuesday, October 16, 2007

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!


Jonas said...

One area with regards to fluid intake in endurance sports, which I don't feel has been adressed in this series, is energy. In endurance events (eg. marathon or ultra-marathon) I think we can agree that athletes need some kind of energy input to be able to keep performing.

It is unclear from this series if the different energy drinks have any impact of energy intake, and resulting performance, or if we should simply drink water and get energy from other sources (fruit, gels, whatever).

This area does have some interest for me since I will be running my first marathon next spring, and am still struggling to make heads and tails in all the myth and advice.

Ross Tucker and Jonathan Dugas said...

Hi Jonas,

Thanks for visiting us here at The Science of Sport.

We hear you 100% on your comment. The series on dehydration and fluid ingestion was meant to focus on fluid ingestion and its effects on temperature and fluid balance. It is an entirely new and different series to address carbohydrate ingestion.

With regards to your marathon, don't psych yourself out---the marketing makes it all seem more complicated than it really is. Drink to thirst and aim to ingest about 30-60 g of carbohydrates per hour.

It makes no real physiological difference if the carbohydrate is in liquid or solid form. What is more important is if you can tolerate one or the other, and finding something that you feel works well for you.

Good luck with the training, and be sure to stay tuned as eventually we will address the energy intake issues!

Kind Regards,

machine said...

I realize I'm commenting on a rather old post, but I wanted to ask/add something. Although you wrote that 'it is an entirely new and different series to address carbohydrate ingestion', surely drinking 30-60grams of carbs per hour is easier than eating 30-60 grams of carbs per hour. In addition, although you noted that 'it makes no real physiological difference if the carbohydrate is in liquid or solid form', surely it is easier, and perhaps more efficient to get the carbs in via liquid form than a solid form. as an amateur cyclist, I found it easier to drink as opposed to eat, as eating also tends to influence your breathing patterns.

Ross Tucker and Jonathan Dugas said...

Hi Machine

Thanks for the comments. You're quite right, getting your carbs in a liquid form is quite a lot easier than eating, especially during running where the mechanical act of eating is more difficult too.

In fact, I think this came up in a subsequent post in the series, though for the life of me, I can't remember which one! I tried to find it, but I couldn't. I'm pretty sure it's part of this series though. But basically, what we said is that the ingestion of fluid during exercise is certainly recommended as a means to obtain what is necessary glucose.

In fact, I am of the opinion that the sports drinks companies missed a trick on this one, because they could quite accurately have told people that 400 to 600ml per hour of sports drinks is NEEDED to keep hypoglycemia at bay. Instead, they opted for the fluid/dehydration angle, which is now becoming increasingly suspect. So from a marketing/positioning point of view, it is my opinion that sports drinks should have positioned themselves as energy drinks, not fluid replacement drinks.

So yes, you're right. But the point as far as dehydration goes is that you don't NEED to drink to replace all sweat loss, and that is a distinct issue from the carbs one.

Thanks for the comments!

dominguezmd said...

I congratulate you guys on having a much needed critical, skeptical attitude towards the vast mythology of sports "science". It is a shame that even specialized publications with degree-holding authors propagate a large amount of voodoo mixed with scant scientific data (cult tactics, anyone?)
I am a marathon runner and would like to know your opinion regarding the use of gels in combination with water; as the manufacturers would have it, one should wash down each packet of gel with an amount of water that, once mixed in the stomach, would render a solution with the same caloric concentration as sports drinks. This is supposed to improve absorption, but I'm under the impression that the gels will be promptly absorbed even if a lower amount of water than recommended is ingested along with them. What do you think?