Build a hard core with this deceptively simple exercise

It's hard to believe the plank could provide such a great workout—until you try it. Keith Scott, A.T.C., C.S.C.S., a strength coach in Medford, N.J., recommends conquering the plank before attempting any heavy weight exercise.

Get into pushup position on the floor.
Now bend your elbows 90 degrees and rest your weight on your forearms. Your elbows should be directly beneath your shoulders, and your body should form a straight line from your head to your feet. Hold the position for as long as you can. Your goal should be to hold it for two minutes.

"The plank helps develop strength in the core, shoulders, arms, and glutes,"
says Scott, making it a great prerequisite for lifting heavy weights or playing intense sports. Even though you aren't moving or lifting weight, you have to constantly squeeze your abs to hold the position—most people can't last 30 seconds on their first attempt.