How Strong Is Your Core?

Lie on the floor in standard push-up position with your toes on the ground, but place your elbows instead of your hands on the ground (the classic "plank" position). Maintain a straight line through your body with no arch in your back. Keep your head down and in line with your back. Hold that position for as long as you can.

If you lasted less than 15 seconds: The core muscles in your abdominals and lower back are on the weak side, making you more vulnerable to acute or chronic lower-back pain.

If you lasted 15–45 seconds: You've got a nice foundation of strength, which will help protect your back, but there's still room for improvement.

If you lasted more than 45 seconds: Wow, can we see your abs?

Try these exercises to tune up your trunk and strengthen your core.

And read "Why Is Sitting in a Chair for Long Periods Bad for Your Back?" at our partner site, HowStuffWorks.com.