Target area(s): abs, back and shoulders
How to perform a plank:
Start in a table top position, with your hands under your shoulders and your knees under your hips.
Keeping your shoulders in the same position, extend your feet back (hold your abs and tush!) until you are in a straight line from head to feet.
Modification: Instead of the above pose, you can also do this on your forearms if it is too difficult the first few times.