Stability Ball Crunch

The stability ball crunch takes the most common abdominal exercise and gives it back the range of motion the floor removes. Lying with your lower back over the ball, the spine can extend slightly below horizontal before the crunch begins, which means the abdominals start from a lengthened position instead of an already-shortened one. That extra range is the whole reason to use a ball, and it makes each repetition harder than it looks. The instability adds a second demand: the obliques and the deep stabilisers work continuously just to stop the ball rolling underneath you. Position the ball under the lower back rather than the mid back, keep the knees bent at a right angle with the feet planted, and let the hands rest behind the head without pulling on the neck. Pulling the head forward is the fault that turns this into a neck exercise.