http://AskTheTrainer.com/best-core-exercises.html

Personal Trainer Mike Behnken, MS, NASM-CPT-PES, CSCS

The floor plank is a basic core exercise. There are hundreds of progressions to the plank.

You must be able to properly perform the plank in order to get the benefits of the progressions of the plank.

The most important thing to grasp is the posterior pelvic tilt.

Stand in front of a mirror with a pair of pants and a belt on and relax.

If your belt is tilted upwards in the front it means you have anterior pelvic tilt.

You must be able to rotate your pelvis as far as you can the opposite way (posterior) during the plank.

You must maintain this pelvic tilt, along with a drawn in belly button and squeezed butt and leg muscles.

Beginners should hold for a few seconds, rest, and repeat.

There should be no "slipping" back and forth movement with your feet or arms, if there is, the floor is not slippery, you are not performing the exercise properly.

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