This particular machine supports your head, neck, shoulders, and body, allowing you to safely engage in the "jackknife" position that is commonly associated with abdominal workout routines without strain or stress on other body parts.
For a more advanced workout to complete the 6 best ab exercises, you can try the ball tuck-in exercise, sometimes also called the jackknife.
Concentrate on your lower abs as you slowly jackknife your body upwards while rolling the ball down towards your feet.
Slowly jackknife your body upwards as you roll the ball down towards your feet.
Now, when's the last time you saw that jackknife Claudia gave you last summer?