Elizabeth Warren Says She's The Fastest Senator

Elizabeth Warren doesn't need to track her step count or run a stopwatch on her 40-yard dash to know she's the fastest Senator ... and she may very well be right, because our photog had a tough time keeping up with her.

We got the Democratic Senator from Massachusetts in the underground tunnel system under the Capitol and she made our camera man Charlie Cotton work hard to go step-for-step.

Liz was on her way to the Senate for a speech about ICE funding when we chopped it up with her about a ton of topics ... including footwear.

The Senator says she doesn't wear heels because she walks around all day ... and jokes she wears a good pair of sneakers to keep in "fighting shape."

Liz also tells us the secret to her speed-walking and explains why her dog and her husband keep her chugging along in a ruthless town.