ECF volume change after exercise

[jmher0403]

after a vigorous exercise, a 100kg man loses 4kg but sodium level remains constant.What is the ECF volume after exercise?

Im sure 4L of water is lost from ECF. Now ECF:ICF = 36:60 L

Sodium not excreted so osmolarity of ECF increases and some water will move from ICF

how do I calculate how much water moves from ICF? I know that the omsolarity will have to balance but I have no idea how to determine numerically. Any help?

Thanks

[JackBean]

where did you get that sodium is not excreted?

[jmher0403]

becuase it says that sodium level does not change so only water excreted...?

[JackBean]

Imagine you have 10 g of sodium in 1 liter of water, OK? That means that the level of sodium is 10 g/l. Now, you get rid of 200 ml of water, but no sodium. Now you have 10 g in 800 ml, i.e. 12,5 g/l. Is the concentration the same?