The abdominal crunch on an exercise ball came in third on the list of best exercises for the rectus abdominus. This is the conclusion of a study at San Diego State University that compared 13 common abdominal exercises in order to find which ones really strengthen the abs. Each exercise was ranked for muscle stimulation (measured with EMG) in the rectus abdominus and the internal and external obliques.
Here's how to do it right.
1. Crunch on an Exercise Ball
Sit on the exercise ball with your feet flat on the floor.
Let the ball roll back slowly and lie back until your thighs and torso are parallel with the floor.
Contract your abdominals raising your torso to no more than 45 degrees.
To work the oblique muscles, make the exercise less stable by moving your feet closer together.
Let the ball roll back slowly and lie back until your thighs and torso are parallel with the floor.
Contract your abdominals raising your torso to no more than 45 degrees.
To work the oblique muscles, make the exercise less stable by moving your feet closer together.
2. See More of the Best Abdominal Exercises
See the full list of the best and worse ab exercises.

