What muscle - structure am I feeling ??

Hey @aneros_user44152 ,

I feel a knot in my perinuem contract and move around- it's excellent, but what is it?

Hard to tell from distance.

The pressure on the car seat must reveal it when other positions do not.

That makes the Bulbospongiosus the most likely contender. When I learned to identify my pelvic muscles, sitting on a hard chair was very helpful and the Bulbospongiosus was the first and easiest to feel against the chair.

Is the prostate erectile tissue , does it stiffen with blood flowing into it?

As far as I know: yeah, pretty much.

If you want to learn more about your pelvic muscles, have a look at the educational youtube videos linked in the wiki.

Cheers, Unfug