Many fitness-minded individuals, members of the general public and even athletes lack true core strength. They may be able to rip out crunches, but they will colossally fail any true test of core strength. (Read about the death of the crunch.)
Training the core is about more than looking good. It's the foundation of athletic performance, because it transfers force between the lower and upper body and stabilizes movements. If your core is weak, then virtually all sports skills will suffer in one way or another. For non-athletes, core strength is critical for preventing injury during everyday movements, such as lifting objects overhead or even getting out of a car.
Before beginning a true core training program, it's a good idea to test your core strength and stability to see where you stand. You can then address your weaknesses and track progress until you finally achieve a truly strong core. (Read about training your entire core.)
The plank is a true measure of core stability and muscular endurance. It's relatively easy to perform, but it forces your entire core to fire to maintain the position.
This test measures your ability to stabilize your spine. Lowering your legs naturally forces your lower back to arch upward. The stronger your core, the lower you will be able to keep it in a natural position
Degree of legs at end of test
For strength coaches reading this article, I recommend using the Functional Movement Screen Stability Test, developed by Gray Cook. This screening protocol identifies core stability, coordination, strength, mobility and endurance issues that can impair performance and put your client at risk during exercise.