Connotation of "intestinal fortitude"

I have heard the expression intestinal fortitude to mean courage or endurance to achieve something. Is there a connotation for stubbornness in this expression?

As people have mentioned in the comments, intestinal fortitude can be called a euphemism for guts. Guts is defined as "fortitude and stamina in coping with what alarms, repels, or discourages", or by Google as "personal courage and determination; toughness of character".

Both definitions have some mention of tenacity - "stamina" implies an ability to go on without giving up, and "determination" implies willingness not to give up. Similarly, "stubbornness" implies a refusal to give up. Thus I think there are similarities, although "intestinal fortitude" - or "guts" - seems to include the positive side of "stubborn", and not its possible negative connotations.

As a clarification, I am not saying that "guts" connotes "stubborn", nor vice versa, but that both those words strongly connote "tenacity", and in that way there is a link between them.

I would say the answer is simply "no".

Stubborn quite simply means someone who won't change their mind.

(Or indeed, something like say a piece of metal you have to machine could be "stubborn" - hard to change it's shape.)

This quality, stubborn, has nothing to do with "having guts" - like Tom Cruise or John Wayne. If you have guts, you can crawl through swamps, fight nazis, etc.

There's really no relation to "stubborn".

Particularly if the questioner is a non-English speaker, wondering what the phrase means, it's a shame to confuse the questioner.

Quite simply, "intestinal fortitude" is a humorous alternate way to say the slang term "guts". (Like, a street fighter, etc.) No real connection to stubborn.