A Ball is required to properly perform this exercise.
The main focus behind performing the jackknife is to remember to maintain a pelvic tilt (previous exercise of the month) in order to properly activate the CORE musculature and reduce the strain placed on the low back.
The jackknife should be performed as follows:
1. Begin in a push up position with the front of feet on the ball, back flat, and torso parallel to the ground.
2. While maintaining a pelvic tilt, roll the ball towards the body by bending the knees, but maintaining a tight CORE.
3. Return the ball to its starting position by removing the bend in the knees and returning the torso parallel to the ground.
4. An advanced version of the jackknife would be to perform a push up in-between each forward ball roll when the legs return to a straightened position.Copyright CORE Conditioning 2010