Give it a try and you will soon find a wonderful surprise. It is simple in that you only have to hold yourself in a straight plank position yet when you are in this position your abdominals are doing all the work to hold you there.
I do have to stress that you make sure you complete the ab plank properly to get maximum benefit and to properly work your ab muscles. The workout is to complete 4 sets of 60 seconds each set. Determine the proper exercise intensity by starting with this first test.
1. Start by getting on your kneeling on your knees and forearms on the floor. Your forearms should be far enough from your knees so that your back is flat and parallel with the ground. Don't sag your hips and they should also not be pointing up to the sky. It should be a nice straight line from your shoulders down to your hips. Try holding this position for 30 seconds. If you can do this comfortably then you will move on to step 2. If 30 seconds is a challenge for you then this is where you will begin and complete 4 sets of 30 seconds each. As you get stronger you extend the time to 60 seconds. Once you complete 4 sets of 60 seconds then move on to step 2.
Once you have reached the 2nd test you will be in the same position as test 1 except your knees won't be on the ground. Your feet will actually be on the ground instead and your forearms. Now you have made your plan more difficult and you will see why when you try this test. Hold this position for the suggested 30 seconds in a straight, flat position. If you can hold this nice and level flat position for 30 seconds with only your feet and elbows on the ground then move on to test 3. If not, then practice this position with 4 sets of 30 seconds each set and again as you get stronger move up to 60 seconds.
Now that you made it through the first two tests you are now ready for test #3. To make it even more difficult you are going to put your forearms on an unstable surface. That surface is going to be a stability ball instead of the ground. This instability will force your ab muscles to work even harder. The same technique applies to this test like you performed tests 1 and 2. The difference is your feet are on the ground and your forearms are on the stability ball.
Some people find that this exercise is terribly fatiguing and their ab muscles cramp and others don't think it is that tiring from a muscle fatigue standpoint. Though the next day their abs are very sore and that is because of the isometric type of contractions that you performed during this exercise. After a few months of this type of ab exercise, eating a healthy meal plan along with cardiovascular exercise your abs should be strong and ready to be displayed.