The plank is an exercise that is good for your core muscles. If you don't have a lot of time throw this in to your daily routine for a big gain in strength! This exercise works your rectus abdominus, lower back, chest, and shoulders.
Start in a push up position, keeping your arms under your shoulders. Legs should be straight out behind you with the feet together. hold for is long as you can. work up to 1 minute.