Why is the plank exercises such an important component to any fitness routine. The reason is because it really activates all of the core muscles that are necessary to making your entire mid section strong. If you are strong enough you can do them on your toes for an extended period of time, but if you are new to the plank, then holding that position on your knees is perfect.
There are a lot of variations of the plank exercise and if you live in the Northwest, I would highly suggest that you contact your local fitness professional or personal trainer Portland to help you learn all of these. Once you get the hand of it, you can then start to incorporate resistance training in the plank position. Have fun with this and always consult a professional if you have any questions.
Portland Oregon Fitness