I asked because I have also noted the tendency to suck up,water like a sponge and an increase of weight after hard training. Particularly when the bout of hard training comes after a period of little or no training.

Not sure I believe it is all blood volume though. I also tend to eat a lot as a response to hard training and get thirsty.

I'm inclined to believe it's more multi factorial, the body knows it's got to re build and respond so it sucks in everything and retains it.

More scope for water retention in muscles than increased blood volume?