You can find this exercise on page 262 of the book Synergistic Golf.
Exercise Type: BIG BALL
Exercise Category: ABDOMINALS, STRENGTH
Lie on floor with arms and legs in the air with ball balancing between toes and fingertips. Keep abdominals engaged pulling belly button to spine. Inhale removing opposite arm and leg away from ball. Take R arm overhead and L leg the other way. Keep both limbs an inch off floor. Exhale and return arm and leg back to ball. Repeat 10x each side.