Marathon Running and Race Support

Weight variation 2kg (2.5 to 3% bodyweight) glycogen?

I weigh myself every morning in the buff and after "ablutions" and have noticed that my weight varies by up to 2kg over quite short periods. e.g. 75kg one morning, upto 76.8kg another. I understand that hydration plays a large role in it but I consider myself well hydrated as I drink 2-3l of drinks per day, tea, milk, water, and am never dehydrated as such. I fact, after runs I'm never massively thirsty (even after a long one). I'm a creature of 'habit" so the morning weigh-in is post "paperwork" so to speak. What can cause such wide variation? I understand the sheer mass of a couple of meals can add up and also that glycogen depletion in muscles after extended exercise can reduce your weight and conversely see increased weight as glycogen reserves are replenished after a run, but can these aspects add up to 2kg difference (2.5-3% variation in weight)?

Could it be that a 75kg weigh-in coincides with a day's long runs glycogen depletion, lighter (mass) meals than usual and maybe a touch of dehydration? And the converse after a rest day(s) better hydration and higher mass meals?

The difference just seems a lot (and from memory my weight prior to taking up running was always much more stable with only 0.5kg variation at most.)

Anyone else have large weight swings? What's the experience of this of us who have trained for HM and M distances? Is glycogen depletion/replacement part if it? I found this article about it which suggests 100g glycogen stored in muscles and 400g in the liver (plus bound water to the molecules) = coincidentally 2kg.

livestrong.com/article/3079...

(Warning - photo of cheese toasty included in article)

My longest run is only 12km to date and total weekly distance 20-30km - so surely not enough exercise to deplete glycogen reserves?

15 Replies
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Weigh yourself once a week. This daily weighing will see natural fluctuations which is why it’s better to refer to the scales less often Twice a week should be ample

I have no idea why all the fluctuation happens but we know it does. Rig might well know the answer 🙂

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The daily weigh is just a habit. The thing is it seems more variable since the running lark. Before I was less variable in weight from day to day. But yeah, not anything to be concerned about, just interesting.

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I think that 2kg is not actually a particularly big fluctuation.

From the period in which you remember (but didn't record?) smaller fluctuations, to the present day, you have changed - you're older, you are taking more exercise etc - probably it's not unreasonable to think that your biochemistry may have altered somewhat. That could include your glycogen transport patterns possibly.

I have noticed in the past that I seemed to have reached a weight plateau a couple of kilos lighter than usual during marathon training (but I am never really monitoring my weight very closely). Mind you, only maybe 18 months ago I was able to run 13 miles before breakfast with just a couple of jelly babies at the halfway point. Can't do that any more :) *

Regarding water weight there are other factors to consider alongside fluid consumption - carbohydrate and salt intake, for example, may affect body fluid levels.

But the short answer is: Dunno :)

*Edit: well, I CAN, but I'd rather not!

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I don’t know an answer more than the fluctuations of water, natural passage etc. 2kg is not an excessive variation though. Tbh this is exactly why I do weigh myself daily and take an average of the week’s results to gauge my weight, rather than weighing once a week which can produce huge apparent variation.

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Ok. Thanks all. Maybe just one of those things, or I'm looking too closely.

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I have always thought similar. After a long run or heavy training session I weigh up to 1-3 lbs heavier. Then around 2-3 days after it drops off. Someone explained that as the muscle heals/ rebuilds after a heavy session there is a slight inflammation of the muscles, when this happens fluid is used to protect and repair the muscles. Water is retained and then After the repair has happened the excess is then released and passed out the body.

It makes sense to me and it always goes.

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Ha! I always wondered why I weighed more after a lot of running and less after a break. That explanation makes sense 👍

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So much lighter after a run (dehydration, glycogen depletion) then much heavier on rehydration, muscle repair fluid retention and glycogen replenishment, then lighter again later once repairs completed?

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What is it that you are worried about? Are you suffering any problems? I personally think we can overthink these things, and I would chuck the scales!!!

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JuJu - Not worried, just curious because it's not " normal " for me, but there again neither is running 27km in last 7 days either!

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Ha ha there we go then!! I know when I did my marathon training I used to weigh myself after a very long run for a laugh as I’d be about a stone lighter from the fluid lost so running deffo makes a difference...

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Hee hee! The ultimate feel good moment!

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Exactly!! All a con though but fascinating to see how much dropped off

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Exactly!! All a con though but fascinating to see how much dropped off

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I've noticed this too, try weighing yourself morning and night and then see the variation!

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