Playing quarterback in the NFL is one of the toughest jobs in all of sports.

You have some of the fastest, strongest, and most shredded athletes in the world—like superstar defender J.J. Watt and workout stud James Harrisontrying to rip your head off, all while you’re trying to find the open receiver, throw an accurate pass, and move the chains down the field.

There are only 32 starting quarterback jobs in the NFL, and they’re not so easy to hold on to—well, unless you’re Aaron Rodgers, Tom Brady, Cam Newton, or Russell Wilson.

Each QB has to have a combination of speed, arm strength, agility, and mental toughness. If you don’t, you’ll probably find yourself in the CFL, on the bench, or out of the sport altogether.

Here’s a look at the fittest QBs in the NFL for 2017.