Plank

The plank exercise ranked number 10 in the ACE study and is a great way to build endurance in both the abs and back, as well as stabilizer muscles. 

To do it right:

1. Lie face down on mat resting on the forearms, palms flat on the floor.
2. Push off the floor, raising up onto toes and resting on the elbows.
3. Keep your back flat, in a straight line from head to heels.
4. Tilt your pelvis and contract your abdominals to prevent your rear end from sticking up in the air. 
5. Hold for 20 to 60 seconds, lower and repeat for 3-5 reps.