You want strong, defined abs, and you’re willing to work hard for them, right? Then get on the floor and bust out this 100-rep crunch workout. This circuit involves five crunch variations. Do 10 reps of each and repeat this 50-rep circuit twice.
Or for an even more intense ab-burn, do each exercise for 20 reps and do all 100-reps at once. If this is more than your abs can handle, just do five reps of each and repeat that 25-rep circuit four times, taking breaks when you need to.
Source: 100-Rep Crunch Workout : PopSugar