fluid weight loss during swim

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

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?

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

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.

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.

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

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

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

This study looks at how much fluid loss occurs during swimming: www.swim-city.com/library.php3 It seems to be based on the assumption that weight loss is the sum of urination and sweat loss.

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.