http://www.bbc.co.uk/news/health-12042617
Seems that taking on too much water can affect your performance. I don't drink a lot when doing a long run, but a fine line I suppose between being hydrated and not.
http://www.bbc.co.uk/news/health-12042617
Seems that taking on too much water can affect your performance. I don't drink a lot when doing a long run, but a fine line I suppose between being hydrated and not.
He's big and he's good.
I've already posted this on Fetch, but will post again here. This is another example of bad reporting of science. The BBC simply took the 5 summary points from the paper and then made up a story about them.Originally Posted by Silly Big Fella
The abstract is here: http://bjsm.bmj.com/content/early/20...bjsm_ahead_tab
And the full paper is here: http://bjsm.bmj.com/content/early/20...74641.full.pdf
Basically it tells you that weight loss (not just dehydration - important distinction here) is related to how fast you run (although not a conclusive correlation in my opinion), however, the distribution follows the normal distribution (as would be expected) and is pretty much clustered strongly around the mean.
Statistics can be used very wrongly at times - if you want to read more go to http://www.badscience.net/2010/11/1864/ and read about how Stonewall's survey, instead of discovering when Gay men 'came out,' actually proved that people get older as they get older.
Actually I think there is a lot of logic in what has been said, overdrinking leads to low sodium, taken to extremis this can be and has been lethal in marathons.
Any runner who finishes an endurance event without losing some weight is overhydrated to some extent, you should expect to lose up to a kilo of glycogen stores and each gram of glycogen is associated with 2-3 g of water which should also be lost.
The West Highland Way Race studied weight loss with respect to finishing time and also found that the top placed runners had the greatest weight loss.
"Dehydration" I agree is perhaps not the best term to use, but there is a strong possibility that maintaining electrolyte homeostasis is reflected in performance benefits, and that is more important than maintaining weight. That's essentially what Noakes is saying. The fine line is not about maintaining hydration, but maintaining electrolyte balance in the body, (and as I've said before the evidence suggests that drinking electrolyte solutions doesn't help much with this either). Overhydration is also far more dangerous than dehydration.
I think this is an important message to get across, there's a massive industry out there trying to sell salts and sugars as sports nutrition and the more you consume the more profit for them.
"however, the distribution follows the normal distribution (as would be expected) and is pretty much clustered strongly around the mean." Not sure about the relevance of that Fozzy, the paper appears to show a statistically valid correlation between finishing time and weight loss. The weight loss itself follows the normal distribution, so what?
Tim Noakes among others has previously written extensively on the subject (his name is on the paper under discussion), eg: Drinking policies and exercise-associated hyponatraemia: is anyone still promoting overdrinking? from bjsportmed.com T Hew-Butler, TD Noakes - British Medical Journal, 2008 - bjsm.bmj.com
Only slightly off topic; a few years ago the latest educational fad nutters discovered dehydration and brains along with VAK accelerated learning and fish oil and linked water and brains so that all children had to have a bottle of water on their desks and glug away all the time. Result: classroom looks like Tesco's plastic recycling skip i.e. not emptied for two weeks and overflowing and a revolving door fitted because kids spend more time going to the toilet than learning anything. Gawd save us from experts.
Tao begets one. One begets two. Two begets all things.
I wasn't doubting the validity of the research or their conclusions - more the reporting of them in the BBC article. From that article, I got the sense that they were advocating that you shouldn't drink anything and you will therefore run much faster, which is obviously not right.
Regarding my comment on the stats, if you look at Figure 1 in the paper, you see a lovely bell-shaped normal distribution. This is the same distribution you would see if you look at, for example, a statistical analysis for all the heights of the members on this forum, and possibly could be expected.
Figure 2 is the figure where I have the slight issue: the simple mantra of drink less, lose more body weight, run faster as advocated to a certain extent in the paper and strongly in the BBC article is not necessarily true. In fact if you look at the fastest runners in Figure 2, the top 5 were all in the range 0-5% loss, although one of these could actually have gained weight. I'm also not 100% convinced on the validity of the fit in this figure. I could quite happily plot a straight line with negative correlation to that data and argue that it was valid, simply because of the clustering in the 0-5% BW loss. I would need to see more of the statistical methods they've used to come up with the correlation to be completely convinced.
Regardless of the difference between correlation and causation, I've never really thought about this before. Always thought of glycogen as some kind of magic dust that doesn't really have mass. Which is silly I know. Along the lines of the Bad Science fella, Tim Harford's programme on R4 is always a good listen.
Last edited by idler; 22-12-2010 at 03:55 PM. Reason: sp!
the only thing shown in this paper is a correlation (maybe according to Fozzy) between weight loss and finishing time.
everything else is inference.
the dangerous aspect of over-hydration is Potassium loss / dilution - not Sodium.
I'd also suggest that the majority of finishers are unlikely to be overhydrated or to have electrolyte imbalance
From personal experimental experience as a Physiology undergrad overhydration is a highly nauseating experience and hard to maintain (at just one extra litre).
The people who kill themselves through overdrinking confuse the cause of this nausea assuming it is an effect of the dehydration they have been warned about (or the paraquat they think they've drunk (famed example of person who thought they had drunk paraquat from a lemonade bottle stored under the sink and drank water till it killed them, irony being - it was lemonade)) they drink more and compound the problem, feel worse .. +ve feedback.
What of the hydration state at the start ?
More inference here but
Top / fast finisher, more experienced, ensures good hydration on the start line.
bottom / slow finisher, less experience , maybe more likely to start dehydrated.
then there is fuel
fast runner, high rate energy release, uses glycogen and frees water
slow runner, slow energy release, uses fat, burning much less mass and releasing much less water..
ohh...
its all so complicated....
Last edited by andy k; 22-12-2010 at 04:38 PM.
The point is that glycogen does weigh something and you convert it into energy, CO2 and water, and the CO2 you breathe out and the water is available for the normal uses, amongst them sweating - so you should lose some weight, and that in itself does not necessarily mean you are "dehydrated".
Another point is that we drink by time, but sweat by distance, so that the faster runners have sweated a lot, but have not had time to drink much - but unless it is hot or they are an excessive sweater, they will not have suffered as a consequence. PS - and don't forget the 2 to 3 mls of water that is stored with each gram of glycogen - it also becomes available for the body to use....
Last edited by Mike T; 22-12-2010 at 09:09 PM. Reason: spelling/omission
Unfortunately it would cost me £103.40 to accesss the full paper!
Posting Permissions
Reply With Quote