Weight loss DURING a run

13 messages
26/05/2013 at 21:24

If I weigh myself before and after a 12 mile run in hot weather I loss 3 - 4 pounds in weight.....is that 'norma'l?  I would have a couple of gels during the run.

These are fancy bathroom scales that also show your body fat and body water content.  My body water figure has increased slightly after the run which seems odd.

Any thoughts?

26/05/2013 at 21:27
If you didn't take on any fluids during the run then I'd say that sounds pretty normal.
I wouldn't trust the fancy readings on the scales. Apart from the weight the readings are not always accurate.
M...eldy    pirate
26/05/2013 at 21:32

Weighin yourself before and after a run is a good indication of fluid intake needed ....  I wouldnt get too hung up on the fancy scales tho

26/05/2013 at 21:41

I lost three pounds over a 16 mile run last weekend, despite drinking plenty.  It went back on over the following day.

You lose more fluid than you realise, even in cool weather.

26/05/2013 at 22:25

i once read that a lb lost in sweat is 1 litre of lost fluid to replace. Not sure exactly how accurate that is. I lost 6lb last summer on a long run in hot weather. Not sure i would get 6 litres in me.

26/05/2013 at 22:28

Its normal they say its a good idea  to weigh yourself before and after so you get an idea of  how much fluid to drink to replace the lost fluid

27/05/2013 at 06:12

Its 1 kg (2.2lb) lost = 1 litre but don't weigh yourself and if you are 3lbs down neck  1.5 l of water. Drink to thirst so you rehydrate gradually until your pee is normal colour.

27/05/2013 at 06:19

Usually the fitter and more muscled you are the more water your body can store as water due to glycogen (1 grm glycogen, two grms water).

Its possible to drink and retain water this way to such an extent that during a long run in hot conditions its possible to drop several pounds in weight with no fall off in performance.

Needless to say, on returning home to the scales you are now nicely light, Several hours of drinking later you are once again pounds heavier.

27/05/2013 at 15:05

It is normal ( and desirable) to lose  a LITTLE weight due to fluid loss while you run- weight gain suggests a risk of over- drinking and hyponatraemia, 3-4 pounds is less than 2 l- not a big problem. Don't force the drinking to completely avoid weight loss- that would be over-doing it. THese body fat scales work on elelctrical impedence, so many other things will affect readings.

27/05/2013 at 21:20

Many thanks for the comments - I will keep sweating and drinking!

28/05/2013 at 11:48

A quick google suggests you store 15-20g of glycogen per kg of body weight. This would all be used up in a 12mile run. So a 70kg man who is well trained could be using 1000-1400g. That's your 2-3lbs right there.

28/05/2013 at 12:33

Yep I'm the same, lose between 2-4 pounds on a decent run, just put it down to fluid loss.

Goes straight back on when I rehydrate.

28/05/2013 at 13:49

Mostly from breathing.

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