My older brother threw his back out last week. It is pretty bad and he is having difficulty just moving around. He started seeing a physical therapist who has recommended some core strengthening exercises. The first ones she has him doing are flexes that she said he can do anywhere - sitting at his desk, standing in line, etc.
It reminded me of this Adidas ad:
The ad was part of a campaign called "Runners. Yeah, we're different". More ads can be found here.