Primary Muscle Group: Rectus Abdominis

Muscle Groups Worked in This Exercise:  Rectus Abdominis and Obliques

Preparation: Place hands firmly on a stability ball about shoulder width apart as you lean forward with your body fully extended and supported by your feet and hands.  You will be in a diagonal pushup position, leaning forward.

Breathing:  Breath out on the contraction of the muscle and breath back in on the way back to the start position.

Execution: Once balanced in the extended position, drive your left knee upwards towards your chest and squeeze your core muscle group. Repeat and then switch legs.