Core Strength - Super Plank
The super plank is a more advanced motion and should not be attempted until you have succesfully mastered the low plank. The key to this excersise is to try to keep your hips from moving as you transfer between the low and high planks. Start out with 8-10 reps for each set, remembering to alternate starting with your left and your right. As you get better, you can add more reps and do them faster.