Core on the floor is on tap for week 9. This week is planking. The beauty of planks is if you do them correctly, you practice holding your core tight. Every time you move, pick up something, twist, or a hundred other things, you need to hold your core tight. In fact, right now, stand up straight. Stand tall. Now move your belly button toward your spine while keeping your shoulders back and body tall. You will feel your stomach muscles (rectus abdominus and transverse abdominus) tighten. When you are planking, that is how it is supposed to feel.
A strong midsection is absolutely imperative to fitness, athleticism, and staying away from back problems. Planking works the upper legs, the glute, and all the midsection muscles, both in front and in back. Most people tend only to do the sit-up types of movements and neglect the back muscles that support spinal and body stability. Planks put all of them in a wonderful isometric hold to strengthen them all.
Remember, this is a plank and not a hill or a bow. If you put a broomstick that rests on your shoulders and heels, your glute should touch the broomstick. Also, avoid letting yourself sag at the shoulders. Keep those strong and support your neck, which should be in a neutral position. Ready?!