As an experiment today I weighed myself before and after I went for my long run. It was an 11 mile run and the temperature was probably in the low 20s. I lost 5 lbs and 10 ozs. My first thought was that this was all due to sweating in which case it equates to 4.5 pints of water if my maths is correct.
I then thought that this might be a too simplistic way to look at this. I seem to remember reading somewhere that, on average, about 100 calories are burnt for every mile covered so I should have burnt about 1100 calories. Presumably most of this was glycogen. How much does 1100 calories of glycogen weigh? I lost some salt as well but surely this will only have been a few grams? Anything else?
If I did lose something like 4.5 pints of water I then wondered what was the maximum amount of water that I could feasibly or safely lose? I remember when I ran the London Marathon in 1981 I tried taking water on early on and ended up spilling most of it so didn't bother after that (bottled water hadn't been invented then, it all came in cups). It was a hot day so I ran 26 miles without taking any water on. But I was much younger (and dafter) in those days. I also wondered how much others lose. For example how much did Federer lose this afternoon (but he did continually drink between points)? What about Chris on his monster bike ride last week?
Its funny how advice on water intake changes over time. In 1981 I don't remember ever hearing about water even being mentioned. About 10 years ago the vogue seemed to be that you need to drink as much water as possible. A few years ago I think there was some tragedy at the Great North run that may have been caused by taking too much water on and now the advice seems to be not to drink too much?
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6 comments:
It's a useful post - and certainly worthy of another blog debate.
My thoughts are you need to hydrate with water the night before, because liquid takes so long to get into your system. On longer runs, over 1 and a half hours, you need to take on liquid, but this is probably going to help prevent dehydration after your run and not during it.
To be honest I do not drink water on anything other than a marathon. You can't tell me that a few mouthfulls of water on route is going to make all that much difference and so you should be fully hydrated on the start line.
With regards to the weight loss - It makes me laugh when I see people running about in black bin liners in the summer just to shed a few pounds. They will lose weight, but it will be in sweat, which your body will replace as soon as you have a drink.
Now then. Don't want to sound like the smart arsed scientist but i'm afraid its 99.9% water that you have lost. Unless you stopped for a poo half way round.
Yes its true that we break down glycogen but this is part of respiration. In this process we 'burn' food but the only waste products that can be expelled whilst running (or walking) are H20 and CO2. This will happen to a greater extent as the rate of respiration rises. However the glycogen is broken down into solid and liquid waste matter that can only be expelled...well not through your skin or mouth!!!. Also will gases being 22,000 times greater by volume than liquids then one can only conclude that all the weight loss is due to perspiration and not respiration
Here endeth the lesson
ie Tony was right
Hydrate with water the night before!!
Now thats an interesting point of view. There is only one thing which would happen if I did that which would be lack of sleep due to toilet visits!
To be honest water is very quick at entering the body and so long as you are producing frequent, clear urine you are not dehydrated.
When I was younger I found I needed to take no water at all on any training runs and never felt dehydrated but as I've got older I seem to dehydrate much quicker.
This I believe is because as I've got older my kidneys have become less efficient at conserving water back into the body but this may not be true for everybody. Ask Steve Moss who must be the Spen camel and can survive on the longest of runs without hardly any liquid.
As for Old Gimmer losing 5 lbs on a training run I must ask - could you see yourself in the mirror when you returned, as where you lost it from I will never know.
Just out of interest in my younger days I could quite easily lose up to 7 lbs on a 10 mile training run but these days seem to lose hardly anything.
Maybe this is just a reflection on my approach to training these days.
Like Antony suggests, I like to hydrate myself the night before. I find that a minimum 6 pints of bitter does the trick, and some of my best performances have been following this regime.
On a more serious note, when cycling outdoors, the evaporation tends to keep you cool and the tendency is to not drink enough, but indoors on the turbo-trainer, I sweat like a pig. I can't even tackle a session without a towel, headband and still end up soaked. I'll try weighing myself before/after to see what the difference is. Still, I tend not to bother with a drink on anything less than 1.5 hours exercise, and don't feel that it effects me much, this particularly applies to running, since I can't be bothered to carry a bottle.
My personal belief is that most of the weight loss is water. I've no idea how much glycogen weighs, but I would imagine it's very low compared to water which is pretty heavy, so even if the % was high, it would probably account for little in terms of the weight. It would take a brave man to dispute Gareths scientific answer in any case.
About water entering the body quick/slow, I'm pretty sure that it depends to some extent upon the salts/electrolytes that are consumed along-side it. But I'm the guy who just uses el-cheapo diluted fruit juice on my bike rides, and it seems to work just fine.
Good to see the discussion getting started!
I was hoping one of you might know how much glycogen equates to 1100 calories of energy but no one seems to have come up with the answer. I've had to resort to WWW and it tells me that 1 gram of glycogen provides 4 calories so 1100 calories must have been provided by 275 grams of glycogen which is about 10 ozs, so just a bit more than 10% of my weight loss.
I've also seen that glycogen is a type of starch so this will be all converted into C02 and water. I could work out how many litres of gas this is but I'd probably lose my audience if I went down that route. What happens to the water produced by metabolism? - does it go into the body's general water store or is it exhaled??
With regards cycling and your turbo-trainer, Chris: I suppose when you are on the road you get extra cooling by the wind chill factor so a little sweat goes a long way. Its probably similar to running on a treadmill - more sweaty than running outside. I'm also glad you shared the fact that you wear a sweatband with us. What you do in the privacy of your home is up to you.
And Michael, you are correct I don't have 5 lbs to lose. But then again I can't carry 5 lbs of water with me every time I want to go for an 11 mile run! Its hard enough running when you weigh 8 stone dripping wet never mind having to carry that excess water round.
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