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I've recently thought to measure my weight before and after exercise sessions, and was surprised by the result. I assume that the loss over the session is almost exclusively water loss.

Are these sorts of numbers normal, and if not are they a problem?

  • Baseline weight pre-exercise: 93-95kg (6ft 1; male; 32)
  • Over a 25-30 minute run, with no drinking: 1 - 1.5kg weight loss.
  • Over a 1.5 hr elite-level (field) hockey training session, with regular drinking: Drink 1 - 1.5 litres of water, and still have a total weight loss of 1.5 - 2 kg.

(To set a scale for 'elite-level': I don't play international hockey, but ~1/2 the players at the session do/have, and 4 were in Tokyo this year. I'm not 'keeping up' with them; I am just about at a level for it not to be a farce.)

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    This is not really answerable, since everyone has different sweat rates. However, it is not only water loss, but also muscle glycogen use that contributes to the weight difference.
    – JohnP ♦
    Commented Aug 30, 2021 at 14:30
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    @Brondahl - You bring up a good point that a lot of questions related to fitness are prone to "it varies from person to person". However, notice that your question isn't actually closed. I think John's point was merely to point out that it may be difficult to answer. If someone digs up research with values like averages and standard deviations, that would certainly be valuable information. All in all, your question is being positively received, so no need to worry about closing.
    – Alec
    Commented Aug 31, 2021 at 16:58
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    I do wonder if this is one of the distributions with a very high standard deviation. Some people sweat profusely and others hardly at all.
    – Alec
    Commented Aug 31, 2021 at 16:59
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    I do wonder if this is one of the distributions with a very high standard deviation. I agree, that could well be the case. I believe there's a medical condition along the lines of "profuse sweating", so it would be interesting to know whether that's considered qualitively distinct or just "if you go far enough out to the edge of the bell curver then we label it as this thing". Yet more aspects of the question that I don't have the faintest idea about :D
    – Brondahl
    Commented Aug 31, 2021 at 22:23
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    @Brondahl - Hyperhidrosis is the condition you are thinking of, but that's somewhat independent of exercise (And heat, actually). I don't think this is really an answerable question just because of the personal factors, but I did some research and there are some "accepted" rates. I just don't know if any answer(s) would be specific enough for you. :-)
    – JohnP ♦
    Commented Sep 1, 2021 at 16:06

1 Answer 1

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This depends on many factors. Some of these factors are individual (e.g. heat-adapted and larger individuals can on average sweat more). Some of these factors are environmental (e.g. sweating more when it is warm, and less when it is humid).

But here is a ballpark number:

During a thermoregulatory response in a healthy individual, the rate of sweat production can commonly reach 1 to 2 L/hr.

And:

With ample, continuing hydration, a heat-acclimatized individual can sweat up to 4 L/hr during maximal sweating.

TLDR: So yes, your numbers seem very reasonable, especially for your size.

citations

All information from:

  • Medical Physiology - Boron and Boulpaep - 3rd edition page 1218 and 1219
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