People do thousands of sit-ups without every getting the strength or definition they are looking for. You’ll never get the abs you want without learning and practicing great posture. That is because having great abs has a lot to do with the way you stand, walk and run. Real core strength comes from your lower abs and all the muscles around your hips.
The easiest way to understand what we are talking about is to study the Speed and Agility exercises practiced by professional track athletes. There you will find a huge variety of exercises that focus on all these muscles at once. You will also come to understand the specific posture these athletes practice. It is their attention to posture that activates deep core muscles and conditions the athlete to achieve greater power and speed. They also get the fringe benefit of great looking abs and less risk of injury by improving core strength.
These are some of the most rewarding exercises you have never heard of and you can learn more about them here. Posture, Speed & Agility for Great Abs