Question regarding tight breeding.

Hi all. I have a question I'd like to throw out. This is for the sake of curiosity, I don't ever intend to breed. Too many other people doing it who know more than I ever will, so I'll leave it to them.

But my question is this, I understand that when a line of dogs is line bred tightly they can have problems, even with a clean gene pool. Like becoming too fine boned and less robust.

Is that myth? And if it is true, are there any lines that hold up better to tight breeding over a period of time? In otherwords lines that don't need an outcross as quickly as some might.


Thanks for any answers.