How the hell are you guys doing the no hands thing on the train?

Every morning when I'm riding the train I hold on to the handrails for dear life. Sometimes I get lucky and I'm able to stand in the corner place, near the door, and I can lean on it and have my hands free to read a book.

On my unlucky days (which are more frequent), I'm left with no support other than being squished between two strangers and everytime the train jerks I'm flying and falling all over the place.

I have noticed though that some people don't hold on to anything and they're still steady as a rock. So my question is to those people...how the fuck are y'all doing that!?!? Is there some core exercise that everyone's doing that I'm not aware of?