30 Day Plank Challenge FREE PRINTABLE --So you want a simple exercise move that will give you a rock hard core? PLANKS ARE THE ANSWER!! The plank helps develop strength in the core, shoulders, arms and legs. Even though you aren't lifting any weight, you have to constantly squeeze your abs to hold the position. (Most people can't last 30 seconds on their first attempt, that's why we start out with 20 seconds on the first day and gradually build up.)
