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Thread: fluid weight loss during swim

  1. #1
    Very Active Member david.margrave's Avatar
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    fluid weight loss during swim

    In a good workout you lose 1-2 pounds of water. We had a scientist in our group who I haven't seen in a while, otherwise I would ask him, who explained it to me once but I forgot the explanation. It had something to do with osmosis (it is not perspiration in the usual sense), and fluid leaving your body in an attempt to achieve equilibrium with the water you are immersed in. It is the same process that makes fingertips prune up.

    What I'm wondering is what this loss of fluid does to the sodium/potassium balance and is it related to getting cramps after an hour or so.

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    Very Active Member LindsayNB's Avatar
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    Re: fluid weight loss during swim

    I always assumed it was mainly sweat, same as any other intense workout, but less visible...

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    Re: fluid weight loss during swim

    Quote Originally Posted by david.margrave View Post
    In a good workout you lose 1-2 pounds of water. We had a scientist in our group who I haven't seen in a while, otherwise I would ask him, who explained it to me once but I forgot the explanation. It had something to do with osmosis (it is not perspiration in the usual sense), and fluid leaving your body in an attempt to achieve equilibrium with the water you are immersed in. It is the same process that makes fingertips prune up.

    What I'm wondering is what this loss of fluid does to the sodium/potassium balance and is it related to getting cramps after an hour or so.
    You mean it isn't sweat? I'm surprised to hear that. I've always thought it was perspiration, just not apparent because of being in the water. That is the only explanation I've ever heard. If there's another, I'd like to know.

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    Very Active Member __steve__'s Avatar
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    Re: fluid weight loss during swim

    I wonder it those salt sanitized pools are less likely to make your skin prune up.

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    Very Active Member david.margrave's Avatar
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    Re: fluid weight loss during swim

    I don't think it's sweat, but I don't really know for sure.

    I suspect pool water has a lower osmolality than plasma, so I'm confused why water would diffuse from your body to the pool (assuming that's what's actually happening) and not the other way around. I wouldn't be surprised if I have it completely backwards. Like I said I didn't understand his explanation the first time, and I haven't seen him lately to ask again.

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    Very Active Member joshua's Avatar
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    Re: fluid weight loss during swim

    Quote Originally Posted by david.margrave View Post
    In a good workout you lose 1-2 pounds of water.
    Wouldn't that greatly depend on your body weight and the temperature of the water?

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    Very Active Member ourswimmer's Avatar
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    Re: fluid weight loss during swim

    Aside from sweating, you lose water while swimming because the water in the pool pushes harder on your body than does air. It's like wearing a big compression sock.

    The water isn't escaping your body through your skin, though. It's escaping through your kidneys.

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    Very Active Member knelson's Avatar
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    Re: fluid weight loss during swim

    Quote Originally Posted by ourswimmer View Post
    The water isn't escaping your body through your skin, though. It's escaping through your kidneys.
    I don't know about you, but personally I'm not peeing in the pool.

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    Very Active Member ourswimmer's Avatar
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    Re: fluid weight loss during swim

    Quote Originally Posted by knelson View Post
    I don't know about you, but personally I'm not peeing in the pool.
    I think we should stipulate right here to assume that everyone is courteous, sensible, and properly socialized, and thus that everyone gets out for the last step in the dehydration process I described. I certainly never said anything about staying in the pool.

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    Very Active Member magick17's Avatar
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    Re: fluid weight loss during swim

    escaping from your kidneys...is that a good thing or bad thing?

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    Very Active Member knelson's Avatar
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    Re: fluid weight loss during swim

    It doesn't have that effect on me. I rarely have to get out to pee during a workout.

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    Very Active Member orca1946's Avatar
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    Re: fluid weight loss during swim

    B4 practice & after - NEVER during !!! OOHH sick !

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    Very Active Member LindsayNB's Avatar
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    Re: fluid weight loss during swim

    This study looks at how much fluid loss occurs during swimming:

    http://www.swim-city.com/library.php3?id=34

    It seems to be based on the assumption that weight loss is the sum of urination and sweat loss.

  14. #14
    Very Active Member FireRox21's Avatar
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    Re: fluid weight loss during swim

    Quote Originally Posted by __steve__ View Post
    I wonder it those salt sanitized pools are less likely to make your skin prune up.
    Since I only get to train in a saltwater pool, I don't prune up that quick, but it can REALLY dry your skin out if you don't shower and moisturize right after a workout.

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    Very Active Member david.margrave's Avatar
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    Re: fluid weight loss during swim

    Quote Originally Posted by LindsayNB View Post
    This study looks at how much fluid loss occurs during swimming:

    http://www.swim-city.com/library.php3?id=34

    It seems to be based on the assumption that weight loss is the sum of urination and sweat loss.
    I read that study. Maybe it is just sweat. The next time I see that guy who told me it was osmosis, I'll ask more questions.

    Also, I did a little research on rehydrating and what a good level of sodium is, but that can be another subject.

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    Farewell Lily smontanaro's Avatar
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    Re: fluid weight loss during swim

    Quote Originally Posted by LindsayNB View Post
    This study looks at how much fluid loss occurs during swimming:

    http://www.swim-city.com/library.php3?id=34

    It seems to be based on the assumption that weight loss is the sum of urination and sweat loss.
    What about metabolic water production? Any idea how much that is? Is it significant compared with sweating? (Sorry, can't do subscripts):

    C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy (ATP)

    While I'm sure some of that water is exhaled, much of it probably exits through the kidneys as well.

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