Simple Keep Fit Exercises
1). After the first 10 ab crunches, the body starts to get tired and you simply don't perform the exercise properly. You cheat, and instead of using your muscles to carry out the exercise you will tend to start "swinging" instead with no benefit to your muscles at all.
2). Developing any other muscle group seems to be easier, and this is simply because the muscles are larger and show better through layers of fat. You need to lose fat all over your body to make the abdominal muscles stand out, especially the lower abdominal muscles. It is impossible to lose fat from just one section of your body.
The best way of losing weight from all areas of the body is by doing cardio exercises, otherwise known as aerobic exercises. See Cardio Exercises.