Jack-knife on Ball


Utility: Auxiliary
Mechanics: Isolated
Force: Pull



Kneel with chest or waist on exercise ball. Dive over top and place hands on floor with arms extended down supporting upper body. While keeping body horizontal, walk hands further away from ball until shins are positioned on top of ball. With arms vertical and straight, support body off of floor with body straight. See suggested mount onto exercise ball.


Bend hips and knees, allowing shins to roll over top of ball. Pull knees toward chest until heels are under or near glutes. Return by extending hips and knees to original position. Repeat.


Keep arms straight with shoulders positioned above hands. Rectus Abdominis and Obliques only contract dynamically if actual waist flexion occurs. With no waist flexion, Rectus Abdominis and External Oblique act only to stabilize pelvis and waist during hip flexion. If waist flexion were to occur after complete hip flexion, resistive forces are no longer working against abdominal muscles in this final position when knees and hips are flexed. However, abdominal muscles are activated isometrically to keep spine straight when knees are not under body. Also see Spot Reduction Myth and Lower Ab Myth.

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